Modern Graded Science 10

In this defect, the far point of the eye is at infinity, but the near point is greater than 25
cm. In this case, the rays from the object at the near point are focused behind the retina as
shown in the figure (a).

Thus, reading a book held in the hand object retina
is difficult for such a person. This defect is N image
common in old people.

Causes of defect

1. As the eye lens becomes thin and the Fig: 5.30 hypermetropiated eye
ciliary muscles fail to press the lens
for the required thickness, it results in
increase in the focal length of the eye lens.

2. If the eye ball gets shortened, the distance between the eye lens and the retina becomes
less. This also results in increase in the focal length of the eye lens.

Remedy normal
near point
For the correction of this defect, a convex lens of
suitable focal length is used in spectacles. The lenses N
converge the light rays passing from closer objects which convex
are again converged by the eye lens on the retina. It helps lens
to from a clear image of closer objects also on the retina.

Short-sightedness (Myopia) Fig: 5.31 remedy of hypermetropic

It is defined as that type of defect of vision retina
in which a person can see nearby objects without image
any difficulty but cannot see distant objects
clearly. For such a person, the near point is at 25 infinity far point
cm from the eye but the far point is some metres
only. Fig: 5.32 myopiated eye

In this case, the parallel rays coming from
distant objects are focused in front of the retina
as shown in the figure.

Causes of defect

1. When the eye lens becomes thick and the ciliary muscles fail to stretch the lens for the
required extent, it results in decrease in the focal length of the eye lens.

2. If the eye ball gets elongated, the distance of the retina from the eye lens increases. It
results in decrease in the focal length of eye lens.

Remedy concave
lens
For the correction of this defect, concave lens
spectacles of suitable focal length are used. The Fig: 5.33 correction of myopia
lenses diverge the rays passing from distant objects
which are again converged at the retina for the
clear vision of the objects.

LIGHT CLASS - 10 MODERN GRADED SCIENCE 97

Difference between long sightedness and shorted sightedness

Long sightedness Short sightedness

1. A persons with this defect can see 1. A person with this defect cannot see
distant objects distinctly but cannot distant objects but can see the objects
see the objects that are nearby. that are nearby.

2. The focal length of the eye lens is 2. The focal length of the eye lens is less
longer than that of a normal eye. than that of a normal eye.

3. The image of the nearby object is 3. The image of the distance object is
formed behind the retina. formed in front of the retina.

4. To correct this defect, the convex lens 4. To correct this defect, the concave lens
is used. is used.

5. It occurs due to elongation of the 5. It occurs due to flattening of the
eyeball. eyeball.

In this condition, the lens becomes thinner and the ciliary muscles cannot press it to
thicken for required focal length while seeing closer objects.

S me Reasonable Facts

1. Convex lens spectacles are used for the correction of hypermetropia. It is because in a
hypermetropiated eye, the light rays passing from closer objects converge behind the
retina and to converge them on the retina, converging or convex lenses are required.

2. Concave lens spectacles are used for the correction of myopia. It is because in a
myopialed eye, the light rays passing from the distant objects converge before
the retina. To converge the rays on the retina, we have to diverge them for which
diverging lenses or concave lenses are required.

3. Convex lens has positive focal length but concave lens has negative focal length. It is
because the focal length of convex lens is positive and that of negative lens is negative.

4. Concave lens is also called a diverging lens. It is because the lens scatters the beam of
light passing through it.

5. A myopiated person cannot see distant objects clearly. It is because in such people the
eye ball is elongated and the lens of the eye becomes thicker. To see distant objects
clearly the ciliary muscles cannot stretch the lens for the required focal length while
seeing distant objects.

6. A hypermetropiated eye cannot see closer objects clearly. It is because the eye ball of
the eye is flattened.

Things To Know

1. A lens is a transparent medium bounded by one or two spherical surfaces.

2. A convex lens is thicker at its centre than at the edges.

3. A concave lens is thinner at its centre than at the edges.

4. When a narrow parallel beam of light, parallel and close to the principal axis is
incident on a lens, they meet or appear to meet at a point (F) on the principal axis
after refraction through the lens. This point is called focus (F).

5. Focal length is the distance between the principal focus and the optical centre of a lens.

98 MODERN GRADED SCIENCE CLASS - 10 LIGHT

6. The magnification of a lens is defined as the ratio of the size of the image of an object
formed by the lens to the size of the object.

7. The power of a lens is defined as the reciprocal of its focal length expressed in metre.

8. The effect of vision due to which the impression of an image lasts on the retina even
after the removal of the object is called persistence of vision.

9. A person suffering from short-sightedness can see nearby objects but cannot see
distant objects.

10. A person suffering from long-sightedness can see distant objects clearly but cannot
see nearby objects.

Things To Do

To make a model of a short sighted eye, concave lens flask
fix a convex lens on a side of a round bottom convex lens
flask as shown in the figure using cello- fluorescent
tape. The focal length of the lens should solution
be less than the diameter of the flask. Fill
the flask fully with water and add a few
drops of fluorescent solution to it. Shine a
parallel beam of light on the lens. Observe
the position where the light beam converges.

Now, bring a concave lens in front of the convex lens. Shine a parallel beam of light
again through both the lenses. Does the position of the spot, where the light beam converges,
change? Understand the working method of spectacles with the help of this activity.

Test Yourself

1. Multiple choice questions (MCQs).

a. The image formed by a convex lens can be:

A. virtual and diminished B. virtual and magnified

C. erect but of the same size D. virtual but of the same size

b. If the power of lens is -2D, its focal length is:

A. -2 m B. 0.5 m C. -0.55 cm D. -0.5 m

c. The human eye forms the image of an object at its:

A. pupil B. iris C. retina D. cornea

d. The distance of distinct vision for a normal eye is:

A. 0.25 cm B. 25 m C. 0.25 m D. 2.5 cm

e. The image formed by a convex lens is always:

A. real and magnified B. real and diminished

C. virtual and diminished D. virtual and magnified

f. A convex lens forms a virtual magnified image when the object is kept:

A. at 2 F B. between F and 2 F

C. at infinity D. between optical centre and F

LIGHT CLASS - 10 MODERN GRADED SCIENCE 99

g. What is the power of a convex lens of focal length 25 cm?

A. 25D B. 0.25 D C. 4 D D. 0.004

h. Which lens is thicker at the middle and thinner at its edges?

A. concave convex B. concave lens

C. plano concave D. convexo concave

2. Give reason.
a. A convex lens is called a converging lens.
b. Size of pupil enlarges in dark.
c. A concave lens is called a diverging lens.

3. Differentiate between: b. Myopia and hypermetropia
a. Concave lens and convex lens
c. Near point and far point

4. Answer the following questions:

a. Draw a diagram to show how a convex lens forms a magnified and virtual image
of an object.

b. Write a formula of lens and magnification of lens.

c. A convex lens forms a real image of the same size as that of the object. Where is
the object placed? Draw a ray diagram.

d. What is the function of the retina?

e. How does the eye control the amount of light entering it?

f. What is myopia? How is it corrected?

g. What is hypermetropia? How is it corrected?

h. Sanjay sees distant objects comfortably but he wears spectacles while reading a
book.

i. What defect of vision does he have?

ii. Which type of spectacles should he use?

i. If the ciliary muscles of Madhu cannot stretch the lens for required focal length,
what type of defect of vision does she have? Sketch a ray diagram for its correction.

j. A student sitting on the back bench in a class is not able to see the writings on the
board. What type of defect is he suffering from?

k. Sheetal wears a lens of power +2 D. Answer the following questions.

i. What is the defect of Sheetal's vision called?

ii. How is it corrected by using a lens? Show with the help of a suitable diagram.

iii. Name the lens used.

iv. How does she hold a newspaper while reading without using the lens? Why?

l. Define.

i. power of a lens ii. principal focus

iii. real image iv. principal axis

100 MODERN GRADED SCIENCE CLASS - 10 LIGHT

5. Diagrammatic questions retina
image
a. What is the defect of vision of the eye in the given
figure? What is to be done to correct the defect of infinity far point
vision and why?

b. What is the defect of vision in the eye shown in the object retina
given figure? What is to be done to correct this defect N image
of vision and why?

B

c. Complete the diagram and write the features O F 2F
of the image formed.
2F A F

6. Numerical problems

a. A convex lens has a focal length of 10 cm. What is the power of the lens?

b. Determine the size of the real image of 2 cm high object placed 40 cm away from
a convex lens. The real image is formed 80 cm away from the lens.

c. A student wears spectacles of power – 2 D. What type of defect of the eye does
the student have? Find the focal length of the lens used?

d. Nabin uses the spectacles of power +1D. Calculate the focal length of the lens.
What type of defect is he suffering from?

e. A concave lens has a focal length of 25 cm. What is the power of the lens?

f. An object is placed at a distance of 20 cm from a concave lens of focal length 20
cm. Find the image distance.

g. An object is placed at a distance of 20 cm from a convex lens of focal length 15 cm.

i. Find the image distance.

ii. Is the image real or virtual?

iii. Is the image erect or inverted?

a. 10 D b. 4 cm c. - 50 cm
d. 100 cm e. 4 D f. - 10 cm
g. 60 cm, real and inverted

Transparent : allowing light to pass through so that the objects behind can be seen
Pupil clearly
Cornea
: circular opening in the centre of the iris of the eye that regulates the
amount of light passing to the retina by becoming larger or smaller

: transparent outer covering of the eye which protects the pupil and
the iris

LIGHT CLASS - 10 MODERN GRADED SCIENCE 101

Chapter ELECTRICITY AND
MAGNETISM
6
Total estimated periods: 10 (T 8 + P 2)

explain the effects of electric current with examples.
introduce electromagnetic and electrical appliances used in our daily life and tell

their uses (dynamo, transformer, solar battery, battery charger, adaptor, inverter).
explain the safety measures to be practised while using electricity.
solve simple problems related to the determination of cost of electricity.

Electrical energy is defined as the source of energy possessed by change/flow of
electrons in bodies. If it is possessed due to flow of electrons, we call it current electricity.
Current electricity has many common uses in our daily life even though static electricity is
also used for few purposes. Normally, the term electricity is used for the current electricity.
Magnetism is the magnetic property of a body found in magnets. Electrical energy also
shows the magnetic effect. It means electrical energy can be changed into magnetic energy
as well. Electricity and magnetism are very useful in modern life.

Electricity is a very big gift of science to human beings. It is a pollution free renewable
source of energy. It has multi-purpose uses. By using this source of energy, we make our
life easier and more comfortable. It is used for conducting different types of electrical
appliances. Each field of the world is highly influenced by electricity. It is a very popular
source of energy.

D.C. and A.C. R current

If the polarity of an electrical source does not (a) d.c. circuit time
change with time, it is called direct current. Battery and Fig: 6.1 (b) graph of
dynamo are the sources of direct current. Conventional direct current
direction of direct current is from the positive terminal
of a cell to its negative terminal.

102 MODERN GRADED SCIENCE CLASS - 10 ELECTRICITY AND MAGNETISM

Alternating current (A.C.) changes its direction at regular intervals. It is usually
defined as the current used in power supplies. It flows in one direction during the first half
and in the opposite direction in the next half. The figure (a) in the previous page shows an
a.c. circuit. The frequency of electricity supply in Nepal is 50Hz. It means the polarity of
the a.c. changes 50 times in one second. The source of the a.c. is an a.c. generator.

Difference between direct current and alternating current

D.C. A.C.

1. Polarity of direct current does not 1. Alternating current changes its

change with time. magnitude continuously and reverses

its direction periodically.

2. D.C. voltage cannot be altered by 2. A.C. voltage can be altered by

transformers. transformers.

3. It is generated by battery and dynamo. 3. It is generated by an a.c. generator.

Effects of electric current

Electrical energy can be transformed into different forms of energy. This is called
effects of an electric current. Some of the effects of an electric current are as follows:

1. Heating effect

When an electric current passes

through some electrical appliances, they

change electrical energy into heat energy.

This is called the heating effect of an electric

current. Electric iron, immersion heater, a. electric Kettle b. electric radiator c. electric Iron
toaster, kettle, etc. are some such electrical Fig: 6.2

appliances. These appliances have a coil of

wire that converts electrical energy into heat energy. Such a coil is called a heating element. It

has high resistance and high melting point.

The heating element is usually made of nichrome. Nichrome is an alloy of nickel (60%)
and chromium (40%). Its resistance is very high and it produces more heat in a comparatively
short period of time. Its temperature may rise up to 900 °C. Its melting point is 1400°C.

It does not react with oxygen to show corrosive effect. A heating element made of
nichrome is more durable than others. Nichrome may be spoiled by the direct contact
with water. That is why, the electrical appliances which work in water have their element
covered with a metallic sheet.

2. Lighting effect

When an electric current is passed through some electrical appliances, they change
electrical energy into light energy. This is called the lighting effect of an electric current.
Actually, a hot body provides us both heat and light but the ratio of heat and light depends
on the temperature of the hot body. Lighting effect of an electric current is used with
the help of filament lamps, fluorescent lamps and other lighting devices. Here, we shall
discuss filament and fluorescent lamps.

ELECTRICITY AND MAGNETISM CLASS - 10 MODERN GRADED SCIENCE 103

a. Filament lamp terminal
pin
In a filament lamp, a tungsten coil is fitted inside

a glass bulb. The tungsten coil used in it is called aluminium covering

filament. The filament is very thin to increase its thick wire
resistance. The bulb also contains a small amount
of an inert gas such as nitrogen or argon to prevent glass stem
oxidation and evaporation of the tungsten metal at nitrogen gas

high temperature. Two pins help to hold the bulb glass bulb

in its holder. The electric current passes in the bulb supporting wire
through two terminals.
filament of
Working method: When electricity is passed in tungsten

the bulb, the tungsten filament attains a very high Fig: 6.3 filament lamp
temperature and hence it becomes white hot. It then

emits light accompanied by heat. The tungsten is used as filament in lamps because it has

a high melting point (3400°C) and high resistance.

Filament lamps are inefficient. They emit both heat energy and light energy but about
90% of the electrical energy is emitted as heat and only about 10% of the energy is emitted
as light. We have noticed that only the filament of a filament lamp emits light but its other
part does not. Because the filament being very thin, it has high resistance and hence only
it converts electrical energy into heat and light but not the other parts of the lamp.

b. Fluorescent lamp

A fluorescent lamp consists of a discharge A.C. source choke
tube with two electrodes at its ends. It is filled electrode
with mercury vapour and inner surface of the
tube is coated with fluorescent powder. A choke glass tube filled with mercury vapour and
coil provides necessary high voltage to the coated with fluorescent power
lamp. A starter is also used in the circuit.

Working method: When high voltage starter
is supplied between two electrodes of a Fig: 6.4 fluorescent lamp

fluorescent lamp, the mercury, ionises and the electrons flow inside the lamp through

mercury vapour. These electrons collide with mercury atoms and ultra-violet rays are

emitted. The fluorescent powder absorbs ultra-violet rays and emits visible light. Since

mercury is used in a fluorescent lamp, it is also called a mercury lamp. Vapourised

mercury also provides conduction of electricity inside the tube when it is ionized. Before

its ionization, the starter used in the circuit does the same work.

It is more efficient than a filament lamp. It also emits both heat and light, but about
70% of the electrical energy is emitted as heat and about 30% of the energy is emitted as
light. Although initially more expensive than filament lamps, the running costs are far
less because they consume less current and they also last longer.

Difference between filament lamp and fluorescent lamp

Filament lamp Fluorescent lamp

1. It converts 10% of electrical energy 1. It converts 30% of electrical energy

into light thus it provides yellow light. into light thus it gives milky light.

104 MODERN GRADED SCIENCE CLASS - 10 ELECTRICITY AND MAGNETISM

2. It is filled with inert gas like argon, 2. It is filled with mercury vapour.
nitrogen, etc.

3. Its average life is short (about 750-1000 3. Its average life is comparatively long

hours). (about 7000-15000 hours).

4. It is cheap to install. 4. It is expensive to install.

5. It is, in general, round or cylindrical. 5. It is, in general, long cylindrical.

6. Tungsten filament emits light. 6. Fluorescent powder emits light.

3. Magnetic effect

Activity 6.1

Hold a conducting wire AB over a compass needle so that they are parallel to each
other. If an electric current is passed through the wire, they are no longer parallel but
the compass needle is deflected.

A AA

N current N
N current

S S S

B B B
a. wire A B holding parallel to b. flowing current c. reversing the
through the wire A B direction of current
the compass needle

Fig: 6.5

On reversing the direction of current through the wire, the direction of deflection
of the compass needle also reverses. If the current does not flow through the wire, the
compass needle comes parallel to the wire. This experiment shows when an electric
current is passed through a conducting wire, it produces a magnetic field around itself
and thus affects the compass needle.

Hans Christian Oersted discovered the magnetic effect of current in 1819 AD. The
experiment mentioned above was demonstrated by Oersted to support his discovery.
Thus, it is also called Oersted's experiment. When an electric current is passed through
a conductor, it behaves like a magnet. This is called magnetic effect of electric current.

a. Magnetic field around a straight wire

current

direction of current

conductor

magnetic direction of
lines of force
(a) lions of force around lines of force right hand
a straight wire
(b) Flemming's right

Fig: 6.6 hand thumbnail

ELECTRICITY AND MAGNETISM CLASS - 10 MODERN GRADED SCIENCE 105

The area around a magnet to which the magnet can influence other bodies by its
magnetic force is called the magnetic field of the magnet. A current flowing through a
conducting wire also has a magnetic field around it.

To find the magnetic field around a wire carrying current, we can use the right-hand
thumb's rule. For this, imagine that a wire carrying current is grasped by the right hand
and the thumb points at the direction of electric current; the rest fingers give the direction
of magnetic lines of force around the wire. The tangent at any point on the lines of force
gives the direction of the magnetic field at that point.

b. Magnetic field around a circular wire circular wire card board
lines of force
When an electric current is passed
in a circular wire adjusted as shown
in the figure, the iron filings scattered
on the cardboard adjust in rings when
the board is hit gently. The rings show
the lines of force around the wire.
The direction of lines of force can be
determined as that for a straight wire
as mentioned above.

Fig: 6.7 lines of fo+rce around–a circular wire

c. Magnetic field around a solenoid

A spiral adjustment of an insulated lines of force
wire is a solenoid. When an electric current solenoid
is passed in it, it shows two magnetic poles
as in a bar magnet.

Its poles can be determined by the right SN
hand's grip rule. It states that if the solenoid +–
is gripped by the right hand in such a way
that the fingers are in the direction of the Fig: 6.8 lines of force around a solenoid
current flowing in the wire, the thumb will
point to its north pole. The opposite pole
will be the south pole.

Electromagnet iron bar

A solenoid behaves like a magnet during the flow of an solenoid
electric current through it. This is known as an electromagnet. It
is a temporary magnet because it loses magnetic properties if no
current flows through it.

Electromagnets are used in many instruments like radio,
telephone, telegraph, etc. Their magnetic strength and polarity both
can be changed. Can you say, how? Discuss in the class.

battery

pins switch
Fig: 6.9 electromagnet

106 MODERN GRADED SCIENCE CLASS - 10 ELECTRICITY AND MAGNETISM

Activity 6.2
A solenoid is made by winding a length of insulated wire around a magnetic

material such as an iron bar. In the figure, a long insulated copper wire is wound around
an iron bar. The two ends of the wire are joined with a key and battery.

Working method: Switch on the key and bring some pins near the one end of the
iron bar. These pins are attracted. If the key is switched off, no current flows in the
circuit and the pins fall immediately. Thus, the iron bar behaves as a magnet only if an
electric current is passed through the insulated wire which winds it. So, it is a temporary
magnet. The strength of an electromagnet depends on the following factors:

1) Current through the insulated wire: High current through the wire increases the
strength of an electromagnet while low current decreases its strength.

2) Number of turns of insulated wire: If the number of turns of the insulated wire
around the magnetic material is increased, the strength of the electromagnet
also increases. By decreasing the turns of the insulated wire, the strength of the
electromagnet is reduced.

3) Nature of magnetic materials: Soft magnetic materials increase the strength of the
electromagnet more than hard magnetic materials.

4) Distance between two opposite Poles: If the electromagnet is 'U' shaped, by
decreasing the distance between the two poles also, we can increase the magnetic
strength.

Characteristics of an electromagnet

1. It is a temporary magnet.
2. Its magnetic strength can be altered.
3. It does not get demagnetized by its storage for a long time.
4. Its poles can be reversed.
5. It can be very powerful too.

Due to the above characteristics of an electromagnet, it is more useful than a permanent
magnet. That is why, electromagnets are used profusely.

Uses of electromagnet

Some important uses of electromagnets are as follows:
1. Electromagnets are widely used in electrical appliances such as loudspeaker, radio,

television and electric bells.
2. They are used in industries for lifting and transporting steel plates, girders, scrap

iron, etc.
3. They are also used for removing magnetic particles such as small steel particles from

the eyes of a person.
4. They are used in separation of magnetic bodies from garbage.

ELECTRICITY AND MAGNETISM CLASS - 10 MODERN GRADED SCIENCE 107

Electric bell

Structure switch +–
battery
An electric bell is a source of sound
that converts electrical energy into kinetic spring
energy and then into sound energy.

An electric bell consists of a U-shaped s
soft iron core around which an insulated
wire is wound to make it an electromagnet. x screw nail
A soft iron armature is adjusted in front of n

soft iron armature

the electromagnet. Its one end is fixed while electromagnet gong hammer
the other end is connected with a hammer
which is free to move. Nearby the hammer,
a gong is adjusted in such a way that the

hammer can beat the gong. The armature is Fig: 6.10 electric bell
connected with a screw at point x.

Working method: When the key is closed, the electromagnet attracts the armature.
Due to this, the hammer strikes the gong and the bell rings. As soon as the armature is

pulled by the electromagnet, the current in the circuit is automatically switched off. This
is because the circuit gets broken at point x. In this situation, the electromagnet loses its

magnetism and it no longer attracts the armature; thus the armature returns to its original
position. The circuit is now completed and the current flows in the circuit. The cycle is

repeated again and again and the bell keeps on ringing unless the switch is turned off.

4. Chemical effect

When a current is passed through a liquid, it undergoes some chemical changes.
The effect is called chemical effect. For example, water with a small quantity of dilute
H2SO4 splits into hydrogen and oxygen when electricity is passed through it. It shows
that water undergoes a chemical change by the flow of electricity in it. The process is
called electrolysis of water. Electrolysis is the process of decomposition of an electrolytic
solution into its constituent passing an electric current through it.

By the process of electrolysis of water, H2 and O2 can be manufactured. By the process
of electroplating, one metal can be coated on another. All of them are examples of the
chemical effect of an electric current.

Interrelation between electricity and magnetism

In 1819 AD, Oersted discovered that an electric current flowing through a conductor
produced a magnetic field around it. This showed that magnetism can be produced from
electricity. Ever since Oersted's discovery, scientists remained occupied with the problem
of how to bring about the reverse effect i. e. how to produce electricity from magnetism. In
1831 AD, Michael Faraday, an English scientist, after a series of experiments, discovered
that it was possible to obtain electric current in a circuit from a magnetic field.

Magnetic flux and its variation

We know that magnetic lines of force start from the N-pole of a magnet and enter the
S-pole externally. Internally, these lines of force move from the S-pole to the N-pole. That is,

108 MODERN GRADED SCIENCE CLASS - 10 ELECTRICITY AND MAGNETISM

the magnetic lines of force are always closed. Suppose a bar magnet is placed at rest facing
its N-pole towards a coil. Some magnetic lines of force will pass through the coil while
going from its N-pole to the S-pole. The number of lines of force passing through the surface
of the coil is a measure of lines of force through this surface as shown in the figure (a).

Magnetic flux through a surface is defined as the number of magnetic lines of force

passing through the surface held perpendicular to closed coil
these lines of force.
magnet

The magnetic flux through the surface of the coil Fig: (a)

increases either if the magnet or the coil is moved closed coil
closer to one another as shown in the figure (a). This
is because the number of magnetic flux through the magnet
surface of the coil increases in this case. Conversely, it Fig: (b)

decreases when they are moved away from each other Fig: 6.11 change in magnetic flex

as shown in the figure (b).

Electromagnetic induction conductor motion

In the figure, a segment of the coil is kept motion
in the magnetic field of a strong magnet. As the
conductor is moved down between the poles galvanometer galvanometer
of the magnet, there is a momentary deflection
of the galvanometer's pointer indicating a (a) moving conductor (b) moving conductor
flow of electric current (Fig: A).
towards magnet Fig: 6.12 away from magnet
Raising the conductor between the poles
of the magnet (Fig: B) results in another
momentary deflection of the galvanometer,
this time in opposite direction. It is due to
electromagnetic induction.

The galvanometer shows deflection only when there is relative motion between the
coil and the magnet. The induction of an electric current in the closed coil, when there is
relative motion between the coil and the magnet, is due to change in magnetic flux.

Thus, whenever the magnetic flux is linked to a closed circuit changes, an e.m.f.
is induced in the circuit which is called induced e.m.f. This phenomenon is called the
electromagnetic induction. The resulting current by electromagnetic induction is called
induced current.

Faraday's laws of electromagnetic induction or principle of electromagnetic induction
This law was propounded by an English physicist named Michael Faraday in 1831 AD.
It is also called the principle of generators. It states that-

1. Whenever magnetic flux linked with a closed circuit changes, an e.m.f. is induced in
the circuit.

2. The induced e.m.f. lasts as long as the change in the magnetic flux is taking place.
3. The magnitude of the induced e.m.f. is directly proportional to the rate of change of

the magnetic flux. Mathematically:
Induced e.m.f. ∝ rate of change of magnetic flux linked with the circuit.

ELECTRICITY AND MAGNETISM CLASS - 10 MODERN GRADED SCIENCE 109

Some electrical appliances

1. Generator or dynamo

The machines used to convert mechanical energy into electrical energy are called electrical
generators or dynamos. They are based on the principle of electromagnetic induction.

Usually, a dynamo is used to induce current in less amount and a generator is used to
induce electric current in a large scale.

It should be noted that the name generator is actually a misnomer, as no energy is
being generated by it but it is only converted from one form to another. A generator or
dynamo converts kinetic energy into electrical energy.

a. Bicycle dynamo cap or head

Structure: A bicycle dynamo consists of a permanent magnet axle
and a coil of a insulated copper wire wound on a laminated soft magnet
iron core. The coil is kept in the magnetic field of a magnet. The case
magnet is connected with the cap or head of the dynamo with an coil
axle. to light
Fig: 6.13 dynamo
Working: When the wheel of the bicycle rotates, it causes the
head of the dynamo to rotate, which in turn rotates the permanent
magnet. Thus, the magnetic flux passing through the coil changes
and an e.m.f. is induced in it. It is d.c. in nature.

b. Generator

Activity 6.3 magnet
match box
Make several turns (about 500 turns) of an
insulated wire around an empty match box as solenoid
shown in the figure. Connect the ends of the wire
to a sensitive galvanometer. Move the magnet Fig: 6.14
in and out of the box. Observe the deflection in
the galvanometer. Is there any deflection in the
galvanometer when the magnet is at rest in the
solenoid?

A generator is based on the principle of generators or electromagnetic induction.
There are two types of generators: a.c. generator and d.c. generator. An a.c. generator
induces a.c. current (or a.c. voltage) and a d.c. generator induces d.c. current (or d.c.
voltage). Here, we will study about the a.c. generator only.

Structure

A generator consists of magnet, armature, rings and carbon brushes. The armature
consists of a rectangular coil of insulated copper wire wound on a laminated soft iron core.
It is capable of rotation about an axis perpendicular to a uniform magnetic field produced
by an electromagnet. The ends of the coil are connected to the copper rings called slip
rings. When the armature rotates, the rings also rotate. The rings are insulated from each
other. There are two carbon brushes which press lightly against each ring. These brushes
are connected to the external load resistance. In this model, a galvanometer is connected.

110 MODERN GRADED SCIENCE CLASS - 10 ELECTRICITY AND MAGNETISM

Working: When the coil is rotated in the magnetic field, the magnetic flux passing

through the coil changes and by Faraday's law e.m.f. is induced in it. The induced e.m.f. is

a.c. in nature. The mechanical energy needed for the rotation is obtained from a water
motion
turbine or steam turbine or wind power or petrol,

diesel, etc.

In a generator/dynamo, the magnitude of

induced e.m.f. can be increased by the following

methods:

1. by increasing the number of turns in the coil.

2. by increasing the strength of magnetic field. armature field magnet
slip rings
3. by increasing the speed of rotation of the brushes
coil in the magnetic field or by increasing the

speed of rotation of the magnet near the coil.

4. by decreasing the distance between the coil

and the magnet. galvanometer Fig: 6.15 a model of an a.c. generator

2. Electric motor

We know that when a current passes through a Fig: 6.16 electric motor
conductor, a magnetic field is produced around it. If
conductor is kept in a magnetic field, there is mutual
attraction or repulsion between the magnetic field, due to
the current carrying conductor and the magnetic fields.
As a result, the current carrying conductor moves if it is
allowed to do so.

This result is also expected on the basis of Newton's third law of motion. If an electric
current flowing in a conductor exerts a force on a magnet, then the magnet also exerts an
equal and opposite force on the current. When a current carrying conductor is kept in a
magnetic field, the conductor moves if it is allowed to do so. This is called motor effect.

The machine used to convert electrical energy into mechanical energy is called an
electric motor. It works on the principle of motor effect. It is used in domestic appliances
such as electric fans, washing machines, vacuum cleaners, refrigerators, water pumps, etc.

Activity 6.4 enamel is coil of enameled wire
removed
Adjust a dry cell, a coil and two paper clips enamel is
as shown in the diagram. removed

Now, take a powerful magnet close to the paper
coil and observe the motor effect. Remember clip
the coil should be of thin wire maximum with
10 turns. The ends of the coil should be rubbed –+ dry cell tape
with sand paper for conduction.
Fig: 6.17 motor model

3. Inverter

An inverter is that electrical appliance which stores electric current when electricity
is supplied. During load shedding, it is used as a source of electric current. It is very

ELECTRICITY AND MAGNETISM CLASS - 10 MODERN GRADED SCIENCE 111

popular in our daily life. A device connected to an inverter changes the flowing alternating
current into direct current an stores in the battery connected to it.
When the supply is cut off, the stored direct current in the battery
is changed into alternating current by the inverter. The electric
current is used for many purposes in our daily life.

4. Battery charger Fig: 6.18 inverter

Nowadays,batterychargersareusedinmanyelectricalappliances. Fig: 6.19 battery charger
The appliances are also supplied with batteries which stored direct
current. They battery chargers change supplied alternating current
into direct current to store in the batteries. The direct current stored
in the batteries is used to run the electrical instrument. It is also called
a recharger. There are many types of chargers. Mobile chargers are
very common nowadays. In some battery chargers, there is cut off
system as well. The system disconnects the electric circuit when the
device is fully charged.

5. Solar battery Fig: 6.20 solar battery

Solar battery is an electrical device that changes light energy
into electrical energy. It is also called a solar panel. A solar panel is
a group of solar cells. It may be mobile or fixed at a place.

The battery or solar panel stores the electrical energy in a
storing cell (lead acid battery). The stored electrical energy can be
used for different purposes as a source of electricity.

6. Adapter/Adaptor

An adapter is used to run radio and other electrical appliances
which need less voltage to work. It changes the voltage of a.c. supply
and it also can change a.c. voltage into d.c. voltage. In it, a knob is
used to adjust the required voltage for the electric appliance to run.

7. Transformer Fig: 6.21 adaptor

A transformer is primary coil secondary coil primary coil secondary coil

an electrical device that a.c.
source input
converts low a.c. voltage input voltage
into high a.c. voltage and voltage

vice versa. There are two iron core output iron core output
types of transformers: voltage voltage

step-up transformer and

step-down transformer. (a) step-up transformer (b) step-down transformer

A step-up transformer Fig: 6.22

converts a low a.c. voltage

to a high a.c. voltage and a step-down transformer converts a high a.c. voltage to a low

a.c. voltage. The instrument is based on the principle of mutual induction. It states that

"When a closed coil is kept in a changing magnetic field of the primary coil supplied with

a.c., electric current is induced in the closed coil (secondary coil)."

112 MODERN GRADED SCIENCE CLASS - 10 ELECTRICITY AND MAGNETISM

Structure: It consists of a rectangular soft iron core made of laminated sheets. There
are two coils which are not connected to one another in any way. These coils are wound
on an iron core as shown in the figures. One of the coils may be connected to a source of
a.c. This coil is called the primary coil and the other is called the secondary coil.

The e.m.f. of the a.c. source applied across the primary coil is called input voltage and
the e.m.f. induced across the secondary coil is called output voltage. Let NP be the number
of turns in the primary coil and Ns that in the secondary coil. For a step-up transformer,
NS > Np, i. e. number of turns in the secondary coil is greater than that of the primary coil.
For a step-down transformer, NS < NP.

Principle: When an alternating e.m.f. is applied to the primary coil, a changing
current flowing in it produces an alternating magnetic flux in it. This causes the magnetic
flux linked with the secondary coil to change. An alternating e.m.f. is then induced in the
secondary coil. It is called principle of mutual induction on which transformers are based.

The formula given below shows the relation between the primary and the secondary voltage:

Number of turns in secondary coil(Ns) = Secondary Voltage(Vs)
Number of turns in primary coil(Np) Primary Voltage (Vp)

Uses

Transformers are used in voltage regulators of computer, television, air conditioner,
record player, trolley buses, etc. They are used for doorbells, welding purpose and in
electrical furnaces. The most important use of transformers is to transmit alternating
current over long distances. At the power station, electricity is generated at 19500V and
then transformers are used to step it up to 1,32,000 V. It is then transmitted to far away
places. At sub-stations, the voltage is stepped down to 11,000V and then to 220V for
domestic and industrial purpose. A direct current cannot be altered in this manner because
there is no fluctuation in the voltage, which is necessary for a transformer to work.

Example 1: The number of turns in primary and secondary coils of a transformer are 1600
and 240 respectively. If the primary voltage is 220 V, find its secondary voltage.

Solution:

Here, number of turns in primary coil (NP) = 1600

Number of turns in secondary coil (NS) = 240

Primary voltage (VP) = 220 V
Secondary voltage (VS) = ?

We have,

NS = VS
NP PS

or, 240 = VS
1600 220

or, VS = 220 × 240 = 33 V
1600

Hence, voltage across the secondary coil of the transformer is 33V.

ELECTRICITY AND MAGNETISM CLASS - 10 MODERN GRADED SCIENCE 113

Example 2: A power transmission line feeds input power at 2400 V to a step down
transformer with its primary windings having 2000 turns. What should be the number of
turns in the secondary coil in order to get output power at 220 V?

Solution:

Here, primary voltage (VP) = 2400 V, Secondary voltage (VS) = 220 V
Number of turns in primary coil (NP) = 2000 turns
Number of turns in secondary coil (NS) = ?
We have,

NS = VS
NP VP
or, 2N00S0
= 220
2400

or, NS = 220 × 2000 = 183.33 turns
2400

Hence, the number of turns in the secondary coil of the transformer is 184.

Example 3: If you have an electric iron which works on 110 V only, how will you operate
it, if 220 volt line is available in your house?

Solution:

The electric iron may be damaged if it is directly connected to 220 V line. Using a step
down transformer, 220 V line is stepped down to 110 V. This 110 V is then used to operate
the electric iron.

Electric power

Electricity can be used for doing different activities such as running electric motors,
charging batteries, generating heat, etc. An electric motor converts the electrical energy
into kinetic energy and a heater can change electrical energy into heat energy. The electric
power of a device is the rate at which it converts electrical energy into other forms. The
rate of conversion of electrical energy (rate of doing work) is the rate at which electrical
energy is being supplied to an electrical device.

∴ Electric power (P) = Electrical energy supplied (E)
(E)Time taken (t)

The unit of power is Js–1. It is called watt (W).

∴ 1W = 1j
1s

The electric power of an electrical appliance is 1W if 1 J of electrical energy is converted
into other forms of energy in 1 second.

The relation between W and bigger units is given below:

1 kW = 103 W

1 MW = 106 W

1 H.P. = 746 W (approx. 750W)

If we observe an electric lamp, it is usually marked 60 W, 100 W etc. The lamp marked
60 W shows that 60 J of electrical energy is changed into heat and light energy in one

114 MODERN GRADED SCIENCE CLASS - 10 ELECTRICITY AND MAGNETISM

second. Similarly, an electric heater of 3 kW converts 3 kJ of electrical energy into heat and
light energy in one second.

The electrical power (P) of an electrical appliance is determined by multiplying the
p.d. (V) across its ends and the current (I) through it.

∴ P = I × V ................... (i)

P=I×V

or, P = Q × W [∴ I = Q/t , V = W/Q]
tQ

∴ P = w
t

or, P = V2 ; by placing the value of V from Ohm's law [ R = V , Ohm's law]
RI

P = RI2; by placing the value of I from Ohm's law.

Example 1: A 60 watt bulb is connected to 220 V supply. Find the electric current through it.

Solution:

Here, power (P) = 60 W

Voltage (V) = 220 V

Current (I) = ?

We have

P = I × V

or, 60 = I × 220

or, I= 60 = 0.27 A
220

Hence, the electric current through the bulb is 0.27 A

Example 2: If an electric heater of voltage 220 V consumes 5 A electric current, what is its
electric power?
Solution:
Here,
Voltage (V) = 220 V
Current (I) = 5 A
Power (P) = ?
We have,
P = I × V
= 5 × 220 = 1100 W.

Hence, the electric power of the electric heater is 1100 W.

Commercial unit of energy: kilowatt-hour (kWh)

'Joule' represents a very small amount of energy. Thus, it is inconvenient to use for
trade purposes. In such a situation, we use a bigger unit of energy called kilowatt-hour

ELECTRICITY AND MAGNETISM CLASS - 10 MODERN GRADED SCIENCE 115

which is represented by the symbol kWh. One kilowatt-hour is the energy consumed by an
electrical device of power 1kW for one hour. One kWh is also called one unit of electricity.

Energy = power × time

∴ 1kWh = 1 kW × 1 h

= 1000 W × 3600 s [ 1 kW = 1000 W, 1 hr = 3600 s]

= 1000 J/S × 3600s [∴ 1 W = 1J/s]

∴ 1 kWh = 3.6 × 106 J

It should be noted that kilowatt (kW) is the unit of power but kilowatt-hour (kWh)
is the unit of energy. The meter inside the meter box installed in our homes measures
the electrical energy consumed by us in kWh. If our electricity meter shows a reading
of 150 units in a month, it means that we have used 150 kWh of electrical energy during
the month. To calculate the total cost of electricity consumed due to the use of electrical
appliances, we use electric consumption (EC) = P(kW) × T(h) and

Cost of electricity = E.C. × rate

Example 1: In a house, an electric bulb of 60 W is used for 10 hours and an electric heater
of 750 W is used for 5 hours every day. Calculate the cost of using the bulb and the heater
for 30 days if the cost of one unit of electrical energy is Rs. 8.

Solution:

Here, power of bulb (P1) = 60W = 60 kW = 0.06 kW
1000

Time for the use of bulbs (t1) = 10 × 30 = 300 hr

Power of electric heater (P2) = 750 W= 750 kW = 0.75 kW
1000

EC = EC by bulb + EC by heater

or, EC = (P1 × t1) + (P2 × t2)
or, EC = (0.06 × 300) + (112.5 × 130.5)

∴ EC = 18 + 112.5 = 130.5 unit

Again, cost of electricity = E. C. × rate

= 130.5 × 8 = Rs. 1044

Therefore, the cost of electricity is Rs. 1044.

Example 2: In a hostel 20 electric fans of 60 W each and 40 lamps of 40 watt each are used
for 8 hours daily. Similarly, 5 electric irons of 750 W each and 2 heaters of 2000 W each are
being used for 4 hours daily. Calculate the bill amount of their use for 1 month. The rate
is Rs 9.5 per unit.

Given,

Power of fans (PF) = 20×60 = 1200 W = 1.2 kW
Power of lamps (PL) = 40×40 = 1600 W = 1.6 kW
Power of electric iron (PI) = 5×750 = 3000 W = 3 kW
Power of heaters (Pn) = 2×2000 = 4000 W = 4 kW

116 MODERN GRADED SCIENCE CLASS - 10 ELECTRICITY AND MAGNETISM

Times for using fans and lamps (tFL) = 8×30 = 240h

Times for using irons and heater (tIh) = 4×30 = 120h
Rate = Rs. 9.5/unit
For total electric consumption–
EC = (PF + PL × tFL) + (PL + Pn × tIh)
or, EC = (1.2 + 1.6 × 240) + (3 + 4 × 120)
or, EC = 672 + 1440 = 2112 unit
Again for the bill amount-
Cost = EC × rate
= 2112 × 9.5
= Rs 20064/-
Thus, the bill amount for the electric consumption will be Rs 20064/-

Safety measures while using electricity

Electricity is very useful energy. Thus, it is a good friend to us. But it may be a big
enemy when we use it carelessly. We should follow the following safety measures while
using electricity to make it our good friend.
1. Colour code of wires should be followed during wiring in a house.
2. Switches and fuses should be connected with the live wire.
3. Fuses of suitable capacities should be used at suitable places in each circuit.
4. Light circuit and power circuit should be made separate while wiring in houses.
5. Wiring should not be done at damp and unshaded places. Quality wires should be

used for the purpose.
6. Heavy electrical appliances should be earthed properly.
7. Switches should not be touched with wet hands.
8. Naked ends of wires should be covered properly using a seal tape.
9. We should wear thick rubber-sole shoes while repairing the electrical appliances in a

circuit.
10. All the electrical appliances must be connected in strong connection in the electric

circuit.

S me Reasonable Facts

1. Coloured wires should be used in household wiring. This is because wires of different
colours used for live, neutral and earth wires help to connect appliances properly
which saves us from electric shocks. Coloured wires also help a lot during repairing
an electrical appliance.

2. Metallic body of heavy electrical appliances is connected to earth wire in a circuit. It is
for the safety of consumers because, when there is a current leakage in the equipment,
the current goes to the earth through the earth wire. A consumer does not get electric
shock, when they come in the contact of the appliance.

ELECTRICITY AND MAGNETISM CLASS - 10 MODERN GRADED SCIENCE 117

3. Soft magnetic materials are used for making electromagnets. This is because such materials
get magnetized and demagnetized easily, which is necessary for a temporary magnet.

4. An electric generator converts mechanical energy into electrical energy. On the other
hand, an electric motor converts electrical energy into mechanical energy. Thus, input
for a generator is output for a motor and vice versa.

5. If a direct current is applied to the primary coil of a transformer, it does not produce a
varying magnetic field in the coil. Thus, there is no change in the magnetic flux linked
with the secondary coil, due to which there is no current induced in it. Therefore, the
transformer does not work for the direct current.

6. Electricity and magnetism are inter-related. A current carrying a conductor produces
a magnetic field around it. On the other hand, when there is relative motion between
a magnet and a conductor, electricity is produced in the conductor. Thus, electricity
can produce magnetism and magnetism can produce electricity. Hence, they are
jointly called electromagnetism.

7. Iron core of a transformer is laminated. The core of a transformer is a combination of
a number of rectangular strips of soft iron. These strips are insulated to each other by
shellac or varnish. This is called lamination of iron core. This lamination reduces energy
loss in the form of heat across the transformer. If the core is a single block of iron instead
of laminated core, there will be heating effect on the core and we get less output.

8. Soft iron core is used in a transformer. This is because soft iron core can convert
magnetic energy into electrical energy easily and it increases the magnitude of
induced e.m.f. in the secondary coil of a transformer.

9. A transformer cannot alter d.c. voltage as there is no fluctuation in the current
magnitude for the change in magnetic flux in the primary coil. Unlike it, in a.c. voltage,
the magnitude of an electric current fluctuates that causes change in the primary coil
and due to it mutual induction occurs in the coil.

Things To Know

1. Some effects of an electric current are (i) heating effect, (ii) lighting effect, (iii) chemical
effect and (iv) magnetic effect.

2. Nichrome is an alloy of nickel (60%) and chromium (40%).

3. When an electric current is passed through a conductor, it behaves like a magnet. This
is called magnetic effect of the electric current.

4. When a piece of soft iron is wrapped many times by an insulating wire and an electric
current is passed through the wire, the iron piece behaves as a temporary magnet.
Such a magnet is called an electromagnet.

5. Electromagnets are used in telephones, telegrams, etc.

6. Magnetic strength of electromagnets can be increased by increasing the number
of turns of wire in a solenoid, passing more electric current and using a more soft
magnetic body.

7. Whenever there is a change in magnetic flux linked with a closed coil, an e.m.f. is
induced in the wire of the coil; this phenomenon is called electromagnetic induction
and the current induced by this method is called induced current.

118 MODERN GRADED SCIENCE CLASS - 10 ELECTRICITY AND MAGNETISM

8. Dynamos and generators are based on Faraday's law.

9. Dynamos and generators convert kinetic energy into electrical energy.

10. When an electric current is passed in a conductor kept in the magnetic field, the
conductor moves. It is called motor effect.

11. An electric motor is based on the principle of motor effect which converts electrical
energy into kinetic energy.

12. The electrical appliances which alter the a.c. voltage are called transformers.

13. Transformers are of two types. They are step up and step down.

14. Step up transformers increase the a.c. voltage and step down transformers decrease

the a.c. voltage.

15. Transformers are based on the principle of mutual induction and in them Vs = Ns
Vp Np
16. Power is defined as the rate of supplying energy:

power (P) = current (I) × voltage (V) or P = V2 and P = I2R
R

17. One kilowatt-hour is the energy supplied when one kilowatt power is used for one

hour.

18. We must follow the safety measures while using electrical appliances.

Things To Do

Make your own electric water heater.

1. Take an empty lactogen can without wire
lid.

2. Make the bottom open by hitting it with open end twopin
a hammer. of the can

3. Take a wooden piece of that size which wooden
fits tightly inside the can. piece
coil
4. Make fine groves at the opposite sides
of the wooden piece as shown in the
figure.

5. Now, fit a heater's coil (500W or 1000W) tin can
in the groves.
opened by
6. Connect the two ends of the coil with a
conducting wire with the help of a two-pin.

7. Fit the wooden piece in the can.

8. Take a bucket of water place the can horizontally in the water and supply electric
current to heat the water.

Remember, the wires should not connect the can and we should not touch the water
when the two-pin is in the socket.

ELECTRICITY AND MAGNETISM CLASS - 10 MODERN GRADED SCIENCE 119

Test Yourself

1. Multiple choice questions (MCQs).

a. What is the melting point of nichrome?

A. 900°C B. 1400°C C. 1800°C D. 1000°C

b. What element is used to make the filament of an electric bulb?

A. Copper B. Nickel C. Chromium D. Tungsten

c. Who discovered the magnetic effect of the electric current?

A. Fleming B. Dalton C. Oersted D. Faraday

d. On what principle is a transformer based?

A. Electro-magnetic induction B. Motor effect

C. Mutual induction D. Magnetic effect

e. Electrolysis of water is an example of:

A. Heat effect B. Light effect

C. Chemical effect D. Magnetic effect

f. Which instrument among the following changes alternating current into direct
current and direct current into alternating current?

A. Transformer B. dynamo C. Inverter D. Adaptor

g. Which instrument changes lower a. c. voltage into higher a. c. voltage and vice-
versa?

A. Transformer B. dynamo C. Inverter D. Adaptor

h. Which formula is used to calculate power in electricity?

A. P = w × t B. Pflu=oVrIe scent C. P = V× I D. P = t
Which gas is filled in a lamp? w
i.

A. Nitrogen B. Oxygen C. Helium D. Mercury

j. Which instrument is based on the magnetic effect of current?

A. Electric bell B. Electric iron

C. Fluorescent lamp D. Electric bulb

2. Answer the following questions.
a. Which wire (live, neutral or earth) connects a switch? Why?
b. How can the strength of an electromagnet be increased?
c. What is kWh? How is it related to joule?
d. What precautions should we take to avoid electrical hazards in houses?
e. Write Faraday's laws of electromagnetic induction.
f. How is current electricity generated from a bicycle dynamo? What is motor effect?
g. State Fleming's right hand rule. For what purpose do we use this rule?
h. How do we increase the current produced in a generator?
i. Write the working principle of a transformer.

120 MODERN GRADED SCIENCE CLASS - 10 ELECTRICITY AND MAGNETISM

j. Mention the major use of a transformer.

k. An electric motor converts energy from one form to another. Name these two
forms in sequences.

l. A dynamo converts energy from one form to another. Name these two forms in
sequences.

m. Describe a simple experiment which illustrates the truth of Faraday's law of
electromagnetic induction.

n. Write down the type of transformer in which turning of wire in the secondary
coil is less than that of the primary coil.

o. Write a short note on:

i. A.C. ii. Electric bell iii. Adaptor

iv. Solar battery v. Inverter vi. Battery charger

3. Differentiate between:
a. A.C. and D.C.
b. Step up transformer and step down transformer
c. Electric motor and generator
d. Filament lamp and fluorescent lamp.
e. Tungsten and nichrome

4. Give reason.
a. A switch and a fuse should be connected with live wire in an electrical circuit.
b. We should follow correct colour code for wiring.
c. Metallic bodies of electric appliances are connected to the earth wire.
d. A filament lamp is filled with inert gases.
e. A thin coil of tungsten metal is used as filament in light bulbs.
f. Filament is bright but not other wires of an electric bulb when electric current
passes through it.
g. An electric bulb is not filled with air.
h. Nichrome wire is used in a heater.

5. Diagrammatic questions

a. Draw a labelled diagram of

i. Bicycle dynamo ii. AC generator

iii. Step-up transformer iv. Step down transfer

b. An a.c. generator is shown in the diagram. Study it and answer the following

questions. A

i. Label A, B and C.

ii. What type of conversion of energy occurs here?

iii. On what principle does it work?

iv. How does it differ from an electric motor? B
C

ELECTRICITY AND MAGNETISM CLASS - 10 MODERN GRADED SCIENCE 121

c. Study the diagram and answer the following questions.

i. What change is seen in the galvanometer B A
when N-pole of the magnet is inserted in C D
the coil and why?

ii. What change is seen in the galvanometer
when the magnet is placed at rest inside
the coil and why?

iii. What change is seen in the galvanometer
when the magnet is moved fast in and out of the coil and why?

d. Study the diagram and answer the following questions.

i. What type of transformer is shown in S N coil
the diagram?

ii. Label A, B, C and D in the diagram.

iii. For what purpose is the transformer galvanometer 0 2 4 6 8 1012 1416
used?

iv. Mention any two applications of it.

v. What is the cause of laminating A?

6. Numerical problems

a. In a hostel, 200 bulbs of 60 W each are lighted for 6 hours per day and 50 fans, of
75 W each run for 12 hours a day. The energy costs Rs. 7 per unit. Calculate the
energy bill for a month.

b. Calculate the amount of the electric bill of a hostel for 30 days when fifty 40 W
bulbs and ten 50 W fans are used for 10 hours a day at the rate of Rs. 7 per unit.

c. How many units will a 2 kW heater consume in 5 hours? If it costs Rs 7.50 for a
unit, find the total cost of lighting for 5 hours.

d. An electric kettle of 1000 W is used to heat water every day for 2 hours. Calculate
the number of units of electrical energy consumed by it in 10 days.

e. In a house, an electric bulb of 60 W is used for 15 hours and an electric heater of
750 W is used for 10 hours every day. Calculate the cost of using the bulb and the
heater for 30 days if the cost of one unit of electrical energy is Rs 7.

f. A transformer is of 220 V primary voltage and 1000 turns of primary coil. How
many turns of secondary coil will be needed to produce 110 volts from that
transformer?

g. A transformer has 300 primary turns and 2400 secondary turns. If the primary
supply voltage is 230 V, what is the secondary voltage?

h. A transformer has 200 primary turns and 150 secondary turns. If the operating
voltage for the load connected to the secondary is measured to be 300 V, what is
the voltage supplied to the primary coil?

i. A transformer has 1500 primary turns and primary supply voltage is 220 V. Find
the number of turns in its secondary coil to get secondary voltage (i) 12 V (ii) 24
V and (iii) 6 V.

j. Study the diagram and calculate the secondary voltage in it.

122 MODERN GRADED SCIENCE CLASS - 10 ELECTRICITY AND MAGNETISM

1000 turns 400 turns
Vs = ?
k. In a transformer, the number of turns in the
secondary coil is 4 times less. Now, calculate the
magnitude of output voltage for the input 220 V. Vp = 600V

a. Rs. 24570 b. Rs. 5250 c. Rs 75 iii. 41
d. 20 units e. Rs. 1764 f. 500 turns
g. 1840 V h. 400 V i. i. 82 ii. 164
j. 240 V k. 55 V

Resistance : the property of a conductor to oppose the flow of electric current
through it

e m f : the amount of energy converted by a source to show how unit charge
through a circuit

p d : the amount of work done in a circuit by the flow of unit charge
through it

M C B : an improved form of fuse (miniature circuit breaker)

Mains fuse : the fuse used in a meter box or authority's fuse.

Power circuit : the circuit made for the conduction of heavy electrical appliances

Magnetic field : the area around a magnet to which it can affect by the magnetic force

Lines of force : the lines representing the magnetic field of a magnet

ELECTRICITY AND MAGNETISM CLASS - 10 MODERN GRADED SCIENCE 123

Chapter CLASSIFICATION OF
ELEMENTS
7
Total estimated periods: 4 (T 4 + P 0)

interpret periodic law and explain the modern periodic table.
explain the position of elements in the periodic table.

In the early stage of the development of science, chemists knew only few elements.
Thus, study of these elements individually was possible. With the passage of time, many
new elements were discovered. Thereafter, study of all elements individually became
difficult. So, many chemists felt that all the elements should be classified into a few
groups on the basis of their similar and dissimilar properties so that their study would be
scientific and systematic.

Lavoisier made the first attempt towards the classification of elements. On the basis
of the properties of elements, Lavoisier classified 32 known elements into metals and
non-metals. But this classification was unbalanced because most of the elements fell into
metals while only a few of them were non-metals. Moreover, there were few elements
which showed the properties of metalloids i. e. the properties of both metals and non-
metals. Since then many scientists have tried to classify all the known elements in a
systematic way.

Dividing elements in different groups according to their similarities and dissimilarities
in the properties is called the classification of elements. The classification of elements
makes the study of elements easy, scientific and practicable.

Periodic table atomic number

The periodic table is a chart or table of 19 2 eletronic
the elements arranged into columns and rows 8 configuration
according to their physical and chemical
properties. In short, it can be said that the element K 8 element name
periodic table is made up of rows of elements and symbol 2 average atomic
columns. An element is identified by a chemical mass
symbol. A row of periodic table is called a period Potassium
while a column is called a group. The periodic
table can be used to know the relationship among 39.0983
the elements. The number above the element
Fig: 7.1

124 MODERN GRADED SCIENCE CLASS - 10 CLASSIFICATION OF ELEMENTS

symbol is the atomic number while the number below the symbol is the approximate
atomic weight of the element.

Uses of periodic table

a. It gives a clear and distinct classification of almost all elements.
b. It helps for the prediction of new elements.
c. It gives the correct position to elements.
d. It is possible to describe simple properties of elements from the periodic table.
e. It displays the atomic numbers, atomic weights, symbols and names of the

elements along with information about the structure of their atoms.

Mendeleev's periodic table

Dmitri Ivanovich Mendeleev, a Russian chemist was the first person to introduce to the
concept of the periodic table. Mendeleev's periodic table was based on two facts: atomic
mass as well as similarities of the physical and chemical properties of the elements. He
arranged elements in the order of increasing atomic masses. He found that the elements
with similar properties occur together at regular intervals.

This led Mendeleev to state his periodic law which was known as Mendeleev's
periodic law in 1869. Mendeleev's periodic law states that "the physical and the chemical
properties of elements are the periodic functions of their atomic mass". The periodic
function means that the properties of elements go on changing with atomic mass but
are repeated after regular intervals. There is periodic re-occurrence of the elements with
similar physical and chemical properties when they are arranged in the order of increasing
atomic masses or weights.

Mendeleev arranged 63 known elements on the basis of their increasing atomic masses
or weights so that the elements with similar properties could be grouped together in the
form of a chart, called Mendeleev's periodic table. Thus, Mendeleev's periodic table is
defined as the table or chart of the elements arranged into rows and columns on the basis
of increasing atomic masses or Mendeleev's periodic law. In Mendeleev's periodic table
the elements are arranged in vertical columns, called groups (families) and horizontal
rows called periods (series). In this table, the elements having similar properties fall
under the same group while the elements with gradual change in their properties having
the same shell number fall under the same period.

Group Group Group Group Group Group Group Group
I II III IV V VI VII VIII

Period 1 H

Period 2 L i Be B C NO F

Period 3 N a Mg Al Si P S Cl
C r M n F e C o
Period 4 K Ca 1* Ti V

Cu Zn 2* 3* As Se Br Ni

Period 5 R b Sr Y Zr Nb Mo 4* R u R h

Ag Cd In Sn Sb Te I Pd
O s I r
Period 6 C s B a La Hf Ta W Re

A u H g Th P b B i P o At P t

Fig: 7.2 a portion of original Mendeleev's periodic table (1871)

Name given by Mendeleev : 1* Eka - boron, 2* Eka - aluminium, 3* Eka - silicon, 4* Eka - manganese.

CLASSIFICATION OF ELEMENTS CLASS - 10 MODERN GRADED SCIENCE 125

Many elements were not discovered when Mendeleev built the periodic table. So, he
left some gaps in his periodic table for the placement of undiscovered elements. Then he
predicted that the properties of elements which likely to be discovered later would fill the
gaps later by studying the properties of the neighbour elements of the gaps.

Mendeleev named the gap Eka-boron, Eka-aluminium, Eka-silicon and Eka-
manganese. For instance, scandium (Sc), Gallium (Ga), germanium (Ge) and Technetium
(Tc) were not discovered at his time but he had predicted their existence in advance of
their discovery. Later the properties of Eka-boron, Eka-aluminium, Eka-silicon and Eka-
manganese predicted on the basis of the periodic law were found exactly match the
properties of Sc, Ga, Ge and Tc respectively.

Features of Mendeleev's periodic table

The original form of Mendeleev's periodic table contained six periods and eight
groups. However, the modified form of Mendeleev's periodic table had seven periods
and nine groups.

1. Mendeleev arranged all the known 63 elements in increasing order of their
atomic masses. The elements with similar properties came under the same group
after a regular interval.

2. Groups: The vertical columns of elements are groups. The groups were named as I,
II, III, IV, V, VI, VII and VIII. The groups I - VII were further divided into subgroups
A and B. The groups VIII had a set of 3 elements. In the modified form of the periodic
table, the ninth group is named as zero (0) group which contains noble gases.

3. Period: The horizontal rows of elements are called periods. In order to
accommodate more elements, the periods 4, 5 and 6 are divided into two halves.
The first half of the elements were placed in the upper left corner and the second
half of the elements were placed to the lower right corner of each box.

Merits of Mendeleev's periodic table

1. Mendeleev's periodic table helps in the systematic and scientific study of the elements.

2. He classified all the known 63 elements at that time.

3. He left some gaps for the undiscovered elements and predicted the properties of such
unknown elements.

4. He found mistakes in the atomic masses of certain elements like beryllium, gold,
platinum, uranium, etc. during the construction of the periodic table e. g. atomic mass
of beryllium. Mendeleev studied atomic mass of beryllium once again and he found
the mistake and gave the correct atomic mass from 13.5 to 9. Similarly, the doubtful
atomic masses of other elements were corrected with the help of Mendeleev's periodic
table.

5. Mendeleev's periodic table inspired subsequent chemists to discover new elements
as he left some gaps for them.

6. Noble gases could accommodate in a new group in Mendeleev's periodic table
without disturbing the existing order after discovery.

126 MODERN GRADED SCIENCE CLASS - 10 CLASSIFICATION OF ELEMENTS

Demerits of Mendeleev's periodic table

1. Position of hydrogen: The correct position of hydrogen could not be assigned in
Mendeleev's periodic table. Sometimes, hydrogen loses electron like group-I elements
(Li, Na, K, etc.) and sometimes it gains electron like those of group VII elements i. e.
halogens (F, Cl, Br, etc.). Due to this property of hydrogen, it can be placed either in
group I or group VII.

2. Separation of chemically similar elements: Some chemically similar elements have
been placed in different groups. For example, gold and platinum have many similar
chemical properties though they are placed in separated groups i. e. gold is in group
I and platinum in group VIII. Similar defects are seen in copper and mercury, silver
and thallium, barium and lead.

3. Grouping of chemically dissimilar elements: Certain chemically dissimilar elements
have been placed in the same group. For example, less reactive elements like copper,
silver and gold have been placed along with highly electropositive or more reactive
alkali metals like lithium, sodium and potassium in group I. Their properties are
quite different in many aspects.

Similarly, manganese (Mn) is chemically different from halogens like chlorine (Cl),
fluorine (F), bromine (Br) and iodine (I) but all are placed in the same group.

4. Position of isotopes: Isotopes are atoms of same elements which have the same atomic
numbers, similar chemical properties but different atomic masses due to difference in the
number of neutrons present in their nucleus. On the basis of his periodic law, isotopes of
elements must have separate places in the periodic table. But Mendeleev could not give a
separated position for isotopes in his periodic table. For example, two isotopes of chlorine
35Cl and 37Cl should have different places but is assigned only one place.

5. Anomalous pair of elements: Certain elements having higher atomic weights have
been placed wrongly before those with less atomic weights and they do not follow
the periodic law. For example, argon (Ar) having higher atomic weight (39.9) has
been placed before potassium (K) having lower atomic weight (39.1). Similarly, cobalt
(27Co58.9) has been placed before nickel (28Ni58.6).

6. Position of lanthanides and actinides: The fourteen elements from atomic numbers
58 cerium (Ce) to 71 lutetium (Lu) that follow lanthanum are termed as lanthanides
(rare earth elements).These elements have similar properties with that of lanthanum
(La57). The elements from atomic numbers 90 thorium (Th) to 103 lawrencium (Lr)
that follow actinium are termed as actinides (trans-uranium elements).

These elements have similar properties with that of actinium (Ac89). Mendeleev could
not arrange them properly.

7. Position of metals non-metals and metalloids: No attempt had been made to place
metals, non-metals and metalloids separately in the periodic table. Most of the metals,
non-metals and metalloids are placed in the some group. Three elements such as Fe,
Co and Ni are placed in the same group VIII. If these elements were separated, the
periodic functions of Mendeleev's periodic table are lost.

8. Mendeleev's periodic table was not able to explain the atomic properties of the
elements like valency, metallic characters, reactivity, ionization potential, etc.

CLASSIFICATION OF ELEMENTS CLASS - 10 MODERN GRADED SCIENCE 127

Modern periodic table

The limitations of Mendeleev's periodic table forced chemists to believe that atomic
mass could not be the basis after the classification of elements. In 1913, Henery Moseley
in England provided the details that atomic number is a more fundamental property for
classifying elements. This is quite reliable because the chemical properties of an element
depend on the number of electrons in its atom which in turn depends on the atomic
number. That led to state the modern form of periodic law. The modern periodic law
states, "the physical and the chemical properties of elements are the periodic functions of
their atomic numbers." This means that if the elements are arranged in accordance with
the increasing atomic number, then the elements with similar properties are repeated
after a regular interval. The chart or table that is obtained when elements are arranged in
the increasing order of their atomic numbers is called modern periodic table.

Based on the modern periodic law Bohr constructed a long form of periodic table or
modern periodic table.

Advantages of the modern periodic table

Modern periodic table is more helpful to explain and solve the defects of Mendeleev's
periodic table. The following are the advantages of the modern periodic table over
Mendeleev's periodic table:

1. The wrong position of some elements like argon and potassium, cobalt and nickel
due to atomic weights, has been solved by arranging the elements in the order of
increasing atomic number without changing their own places.

2. The isotopes of the same element have the same atomic numbers. Therefore, they find
the same position in the modern periodic table.

3. The position of hydrogen in the periodic table has not yet been solved completely due to
its characteristics of group 1 and group 17. Hydrogen is placed above the alkali metals
in the group IA because of the resemblance in their electronic configuration. However,
hydrogen is not regarded as alkali metals. This makes hydrogen a unique element.

4. The groups of the modern periodic table are divided into sub-groups A and B and
treated as separate, group A and group B because the elements of group A differ in
properties from the elements of group B. It makes the study of elements specific and
easier. But nowadays, the groups are numbered continuously from 1-18.

5. The elements of groups VIII/18 of Mendeleev's periodic table (iron, cobalt and nickel)
are placed between group IIA/2 and IIIA/13 as a sub-group B.

6. It separates metals from non-metals.

7. The representative and transition elements have been separated in the modern
periodic table.

8. In Mendeleev's periodic table, there are eight groups, so it was compulsion to keep
alkali metals and coinage metals in the same cell on the basis of their valency i. e. 1.
But in the modern periodic table, the reactive alkali metals are placed in group IA/1
while the less reactive coinage metals (Cu, Ag and Au) are placed in group IB/11.

128 MODERN GRADED SCIENCE CLASS - 10 CLASSIFICATION OF ELEMENTS

CLASSIFICATION OF ELEMENTS s-Block elements Noble gas
p-Block elements
The periodic table of elements (Representative elements)

Respresentative elements

Period Valance
Shell

n = 1 1s d-Block elements Atomic Number
n = 2 2s2p (Transition elements) Symbol
Name

Atomic Mass

n = 3 3s3p

n = 4 4s3d4p

CLASS - 10 MODERN GRADED SCIENCE 129 n = 5 5s4d5p

n=6 6s4f
5d6p

n=7 7s4f
6d7p

mAelktaallis Amelkaeartltaihnlse f block elements Hologens
Inner transition elements
* Series of Lanthanide elements Fig: 7.3
(57 to 71)

* Series of Actinide elements
(89 to 103)

Characteristics of modern periodic table

1. Elements are arranged on the basis of their increasing atomic numbers in the modern
periodic table.

2. There are seven periods and 18 groups in the modern periodic table.

3. The strong metals like alkali metals and alkaline earth metals are placed on the left
side of transition elements and non-metals at the right-side and metalloids between
metals and non-metals.

4. The inert gases like He, Ne, Ar, Kr, Xn and Rn are kept in the zero group at the
extreme right side of the table.

5. In the modern periodic table, the elements of lanthanides and actinides series which
belong to group III B/13 are kept below the main table in two separate rows.

6. All the groups are divided into two sub-groups, A and B except zero and VIII groups
in the modern periodic table.

7. The modern periodic table is made up of a series of rectangles. Each rectangle gives
us four important information about elements. They are

a. atomic number b. atomic weight

c. name of elements d. symbol of the element

Difference between Mendeleev's periodic table and modern periodic table

Mendeleev's periodic table Modern periodic table

1. Elements are arranged in the ascending 1. Elements are arranged in the ascending

order of their atomic masses. order of their atomic number.

2. It fails to explain the correct position 2. It can explain the position of

of hydrogen, isotopes, lanthanides hydrogen, isotopes, lanthanides and

and actinides. actinides.

3. The number of classified elements is 3. The number of classified elements is
less. more.

4. Has no separate place for lanthanides 4. Has separate place for lanthanides

and actinides. and actinides.

5. There are eight groups. 5. There are 18 groups.

Periods and groups of modern periodic table

Periods

The periodic table consists of seven horizontal rows of the elements called periods.
In a period of the periodic table, elements having gradual change in properties are
placed one after another. On the basis of the number of elements present, there are seven
complete periods in the modern periodic table. As of 2016, a total of 118 elements have
been discovered and completed. If any new element is discovered, it will be placed into
the eighth period. However, the seven periods are divided into four categories. They are
very short period, short period, long period and very long period. Period 1 is very short
period which contains 2 elements while short periods contain 8 elements each. Periods 4

130 MODERN GRADED SCIENCE CLASS - 10 CLASSIFICATION OF ELEMENTS

and 5 are long periods which contain 18 elements each. Similarly, periods 6 and 7 are very
long periods which contain 32 elements each.

The number of periods is equal to the number of shells of the atom in which electrons
are filled as the atomic number increases all elements in a period have the same number
of valence shells but their chemical properties are quite different because the number of
valence electrons is different.

S. No. Period No. No. of elements Types of periods
1 1 2 very short period
2 2 and 3 8/8 short period
3 4 and 5 18/18 long period
4 6 and 7 32/32 very long period

Characteristics of period

All the elements in a period show a uniform gradation in their properties from left
to right. This is also known as horizontal relationship in the periodic table. The following
characteristics of all the elements are found in the periods.

1. Valence electrons: All the elements of a period have different valence electrons in
their valence shell. The number of valence electrons increases from one to eight on
moving from left to right. But the number of shell is the same for all the elements
present in the same period. For example, in period 2, the valence electron of lithium
(Li) is 1, beryllium (Be) 2, boron (B) 3, carbon (C) 4 and so on.

2. Valency: The elements in the same period have different valencies. Across a period
from left to right, the valency first increases from 1 to 4, then decreases to 0. This is
shown for the elements of the third period.

Third period Na Mg Al Si P S Cl Ar

Valency +1 +2 +3 +4 –3 –2 1 0

3. Atomic size: Across a period from left to right, the atomic size decreases as the atomic
number increases. This is because more electrons are added to the outer shell, and
the nuclear charge also increases with the atomic number. As a result, nucleus greatly
attracts the electrons nearer to it. Due to this, the outermost shell contracts and the
atomic size decreases. The variations of atomic size of all the elements of period 2 are
given below:

Elements Li Be B C N O F

Atomic size (nm) 0.125 0.09 0.08 0.077 0.075 0.074 0.072

4. Metallic character: The metallic character decreases as the atomic number increases
while moving from left to right in a period. For example, in period 2, lithium and
beryllium are metals, boron is a metalloid while nitrogen, carbon, oxygen, fluorine
and neon are non-metals.

5. Reactivity: The reactivity decreases on moving from left to right in a period of the
group IA/1 and IIA/2 to IVA/14 and after that it increases up to group VIIA/17. Finally,
the elements of group zero (0)/18 are inactive or inert. For example, in period 2, lithium
is more reactive than beryllium because the single valence electron of lithium is

CLASSIFICATION OF ELEMENTS CLASS - 10 MODERN GRADED SCIENCE 131

attracted by the protons of the nucleus, while 4 protons of its nucleus attract 2 valence
electrons of beryllium. Therefore, it is easier to remove a valence electron from lithium
atom than that of beryllium. Thus, in a period, the reactivity of an element decreases
on moving from left to right from group IA/1 up to group IVA/14.

Similarly, the reactivity of elements increases from left to right in any period of group
VIA/16 and VIIA/17. For example, in period 3, the reactivity of chlorine is the highest
compared to sulphur and phosphorus.

Groups

The elements with similar characteristics arranged in the vertical columns of the
periodic table are called groups. There are nine groups numbered by the Roman number
from I to VIII and Zero (0). Except 0 and VIII groups, the groups from I to VII are divided
into sub-group A and sub-group B. These are numbered as IA, IIA ...... VIA, VII A, IB, IIB
...... VIB and VIIB. Group 0 has no sub-groups but group VIII has three vertical columns.
In this way, there are altogether 18 columns. Thus, there are 18 groups in the long from of
the periodic table. According to the new recommendations of International Union of Pure
and Applied Chemistry (IUPAC), the groups are numbered from 1 to 18 in a sequence.

The group number to which an element belongs to in the periodic table is equal to the
number of electrons present in the outermost shell of that atom of element. However, this
is valid only for the elements of the sub-group A. The elements of a group have the same
number of electrons in their valance shells and hence show similarity in chemical properties.

Characteristics of groups

The elements of a group have similar chemical properties and show a regular trend
in their other properties. This is also known as vertical relationship in the periodic table.
The following features are found in all elements in a group of the representative elements.

1. Valence electrons: The electrons present in the valence shell of an atom of the element
are called valence electrons The number of valence electrons remains the same in a
group. For example, the atoms of all the elements of group IIA have two electrons in
their outermost shell.

Elements of sub-group IIA Electronic configuration
K L MN

Beryllium (Be) 22

Magnesium (Mg) 282

Calcium (Ca) 2882

2. Valency: Valency is defined as the total number of electrons gained or lost or shared by

atoms during a chemical reaction. All the elements in a group have same valency because

they have equal number of valence electrons in the same group. The elements of group

0 have no valency. The valency of all representative

elements in a group is either equal to the group

number (In group IA to IVA) or 8 minus group Lithium is the lightest metal.

number (In group VA too). For example,

132 MODERN GRADED SCIENCE CLASS - 10 CLASSIFICATION OF ELEMENTS

Group ve- Valency Group ve- Valency Group ve- Valency Group ve- Valency
IA 1 1 IIIA 3 3 VIA 6 8-6=2 0 8 8-8=0

3. Atomic size: The distance between nucleus and the valence shell of an isolated
gaseous atom is called atomic size or atomic radii of atoms. The size of atoms increases
uniformly on moving top to bottom in a group of the modern periodic table. This is
because a new shell is being added as one goes down the group. It is measured in
Pico meter (Pm) [1m=1012pm]. For example, in the group IA of the periodic table, the
atomic radius of lithium, sodium potassium, rubidium, caesium and francium are
123, 157, 202, 216, 235 and 256 respectively.

4. Metallic character: The metallic character is the tendency of an atom of an element to
lose one or more elements. The metallic character increases as we move from top to
bottom in a group due to increase in atomic size and decrease in the force of attraction
between the nucleus and the electrons of the valence shell. For example, sodium is
more reactive than lithium.

5. Non-metallic character: It is the tendency of an atom to gain one or more electrons in
the valency shell of the atom of an element when supplied with energy. The non-metallic
character decreases on moving from top to bottom in a group due to increase of atomic
size of the elements. For example, fluorine is the most reactive element of group VIIA.

Difference between groups and periods

Groups Periods

1. The columns of the periodic table are 1. The rows of the periodic table are

called groups. called periods.

2. All elements in the same group have 2. The valence electrons of the elements
the same number of valence electrons. in the same period increase from left
to right.

3. All the elements in the same group 3. The elements in the same periods

have the same of valency. have different valencies.

4. The size of atoms increases from top 4. The size of atoms decreases from left

to bottom. to right.

5. Metallic reactivity increases and non- 5. Metallic reactivity decreases and non-

metallic reactivity decreases from top metallic reactivity increases from left

to bottom. to right.

6. The elements in each group have 6. The elements in a period are not alike

similar properties. in properties.

7. There are 18 groups. 7. There are 7 periods.

Position of different types of elements in modern periodic table

1. Hydrogen: Hydrogen has one valence electron in its valence shell. It has an equal
chance to give the valence electron to others or take one electron from others to become
stable. When hydrogen gives its valence electron to others, it becomes positively
charged (H+) and behaves like the metals of group IA. Like group VIIA elements i. e.

CLASSIFICATION OF ELEMENTS CLASS - 10 MODERN GRADED SCIENCE 133

halogens it can gain one electron from other atoms. In this way, its position is justified
in both group IA and group VIIA of the periodic table. However, it is placed at the top
of the group IA due to its least atomic number i. e. l.

2. Representative elements: The first two groups on the left (group 1 and 2) and the last
six groups on the right (group 13 to 18) involve the fillings s- and p- orbitals with
elements. These groups 1, 2, 13, 14, 15, 16, 17 and 18 represent the main groups of the
periodic table. The elements present in these groups are known as normal or
representative elements.

3. Position of metals, non-metals and metalloids: Alkali Alkaline earth

Metals are usually found on the left side and at metals (1) metals (2)

the centre in the modern periodic table. They lose H Be
elements to form positive ion are good conductors of Li Mg
heat and electricity. Three-fourths of the discovered Na
elements are metals. The metallic characters decrease

across the period from left to right. In a group, from Ka Ca

top to bottom of the periodic table, metallic character Rb Sr
increases. Cs Ba

Non-metals are placed on the right side of the zigzag Fr Ra
line in the periodic table. They have tendency to gain

elements to form negative ion. There are 22 known non-metals, out of them 11 are

found in gases state.

Metalloids are found along the zigzag line between metals and non-metals i. e. they
occupy the right side next to metals. Metalloids are elements which can be have either
as a metal or a non-metals. They are boron (B), silicon (Si), germanium (Ge), arsenic
(As), antimony (Sb), tellurium (Te) and polonium (Po).

4. Group IA or 1: The elements belonging to group IA are lithium (Li), sodium (Na),
potassium (K), rubidium (Rb), caesium (Cs) and francium (Fr). Atoms of these
elements have only one valence electron in their valence shell. They lose one electron
to form monovalent cation like Li+, Na+, K+, etc. These elements are also called alkali
metals because they react violently with water and produce their hydroxides which
are strongly basic. These elements are shiny, soft and very reactive.

5. Group IIA or 2: The elements belonging

to this group are beryllium (Be),

magnesium (Mg), calcium (Ca), strontium
(Sr), barium (Ba) and radium (Ra). Atoms The elements belonging to group IA, IIA....
of these elements have two electrons in VIIA and 0 are called representative or
their valence shell. They lose two valency normal elements because they display a wide
electrons to form bivalent cations like range of physical and chemical properties. The
Be++, Mg++, etc. These elements are called outermost shell of the representative elements
alkaline earth metals because they form may be incomplete whereas the inner shells of
basic hydroxides which are less soluble in an atom of all these elements are completely
filled with electrons. In the representative
water.
elements, the group number represents the
6. Group VIA or 16: The elements of this valency and valence electron of the elements.
group are oxygen (O), sulphur (S),

134 MODERN GRADED SCIENCE CLASS - 10 CLASSIFICATION OF ELEMENTS

selenium (Se), tellurium (Te) and polonium (Po). These elements are also termed as
chalcogens (Gk. chalkos meaning copper) because these elements are found combined
with copper in nature.

7. Group VIIA or 17: The elements of this group are fluorine (F), chlorine (Cl), bromine
(Br), iodine (I) and astatine (At). They have seven valence electrons in their valence
shell. They gain one electron from group IA elements to form a negative ion. These
elements are called halogens because they form salts with group IA elements e.g.
NaCl. These elements are highly toxic in high concentration.

8. Group 0 or 18: The elements belonging to group 0 are Halogens Noble
helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (17) gases (18)
(Xe) and radon (Rn). Except helium, all these elements
have 8 electrons in their valence shell i. e. complete octet He

and stable. These elements are placed on the extreme right F Ne
of the periodic table. They are also called noble or inert Cl Ar
gases because they do not take part in a chemical reaction

and have valency zero (0). Br Kr

9. Transition elements: The elements of groups IB/11 and I Xe
IIB/12, IIIB/13 to VIIB/17 and VIII/18 are called transition

elements. They lie in between the group IIA/2 and group At Rn

IIIA/13 and numbered from 3 to 12. The transition elements

are also called d-block elements because electrons fill the valence shells of the atoms

of the elements having d-sub-shells one by one as the atomic number increases.

Transition elements have 1 or 2 valence elements, that they lose when they form

bonds with other atoms. Some transition elements can lose electrons in their nearby

outermost level. They have properties similar to one another and to other metals but

their properties do not fit in any other group in the modern periodic table. They are

good conductors of heat and electricity. They chemically combine with oxygen to

form oxides.

10. Lanthanides and actinides: There are two more rows at the bottom of the main body of
the modern periodic table. These two series, each having 14 elements are lanthanides
and actinides. The lanthanides and actinides together are inner-transition elements or
rare earth metals. They are also known as f-block elements because they are the series
of elements in which 4f (sub-shell) and 5f are progressively filled. These two series of
f-block elements are placed at the bottom of two separate rows. This helps to save space
and avoid undue sidewise expansion of the periodic table. All the elements of each series
of f-block have similar properties. The lanthanides form the inner transition complex
compounds whereas the actinides include the radioactive elements.

Reactivity of metals

The elements of group IA, IIA and IIIA are metals. The reactivity of metals increases
on moving from top to bottom in a group of the periodic table.

As we move from top to bottom in a group of metals in the periodic table, the atomic
size increases with the addition of the number of shells and the force of attraction between
the nucleus and valence shell decreases. Due to this, the bigger atom(s) can lose the valance
electron(s) more easily than the smaller atom(s). Hence, the tendency of losing the valence

CLASSIFICATION OF ELEMENTS CLASS - 10 MODERN GRADED SCIENCE 135

electron(s) increases and their chemical reactivity increases on moving from top to bottom
in a group of metals.

Period Group IA Atomic Size Reactivity

2 Lithium (Li) N Reactivity increases from top to bottom
2,1 Smallest

3 Sodium (Na) N
2,8,1 Medium

4 Potassium (K) N

2,8,8,1 Biggest

Fig: 7.4 metallic reactivity increases from up to down in a group

Why is potassium more reactive than the sodium?

Both sodium and potassium are alkali metals which belong to group IA in the periodic
table. They contain one valance electron in their valence shell. Since the atomic size of sodium
is smaller than the atomic size of potassium, the force of attraction between the nucleus and
valence shell of potassium is less than that of sodium. So, potassium loses its valence electron
more easily than sodium. Hence, potassium is highly reactive compared to sodium.

Reactivity of non-metals

The elements of group VA/15, VIA/16 and VIIA/17 are non-metals. As we move
from top to bottom in a group of non-metals, the atomic size increases with the addition
of the number of shells and the force of attraction between the nucleus and valence shell
decreases. The force of attraction between the nucleus and valence electrons of smaller
atom(s) is more than that of the bigger atoms. Due to this, the smaller atom(s) can gain the
valence electron(s) more easily with more force of attraction than the bigger atom(s). Hence,
the tendency of gaining the electron(s) in its valence shell decreases and their chemical
reactivity decreases on moving from top to bottom in a group of non-metals. For example,
the elements belonging to group 17 are called halogens. They are the most reactive non-
metals as they gain one electron in their valence shell from other during a chemical reaction.
Thus, they are electronegative elements and give negative ions. The reactivity or electro-
negativity of group 17 elements decreases from top to bottom. This is because the nuclear
attraction to the valence shell decreases due to the increase in the atomic size.

136 MODERN GRADED SCIENCE CLASS - 10 CLASSIFICATION OF ELEMENTS

Period Group VIIA Atomic Size Reactivity
2 Fluorine (F) N Br < cl < F
Reactivity decreases as we move from top
3 Chlorine (Cl) 2,7 Smallest
to bottom
N
2,8,1 Medium

4 Bromine (Br) N

2, 8, 18, 7 Biggest

Fig: 7.5 non-metallic reactivity decreases from up to down in a group

Why is fluorine more reactive than chlorine?
Both fluorine and chlorine are non-metals and belong to group VIIA of the periodic

table. The reactivity of the non-metallic elements of group VIIA decreases as we go from
top to bottom. This is because the atomic size of fluorine is smaller than that of chlorine
due to which the force of attraction between the nucleus and valence electrons of the
valence shell is more in fluorine and it can gain one electron more easily than chlorine.
Hence, fluorine is more reactive than chlorine.

Sub-shells

The atom, having two electrons in its valence shell (only one orbit), is called a duplet
e.g. helium. The atom, which contains 8 electrons in its valence shell, is called an octet e.g.
neon, argon, krypton, etc. The electronic configuration based on 2n2 rule cannot explain
all the electronic configuration of all elements. So, the concept of sub-shell was proposed.
According to this concept, each shell consists of a number of sub-shells, which gives more
accurate explanation of the electronic configuration of all the elements. All the sub-shells
are represented by the letters s, p, d and f. The maximum number of electrons in each
sub-shell is given below:

Main shell Sub-shells

First or K-shell (n = 1) s
Second or L - shell (n = 2) s and p
Third or M - shell (n = 3) s, p and d
Fourth or N – shell (n = 4) s, p, d and f
Fifth or O – shell (n = 5) s, p, d and f
Sixth or P-shell (n = 6) s, p and d
Seventh or Q –shell (n = 7) s and p

The s - sub - shell has got maximum 2 electrons.
The p - sub - shell has got maximum 6 electrons.
The d - sub - shell has got maximum 10 electrons.
The f - sub - shell has got maximum 14 electrons.

CLASSIFICATION OF ELEMENTS CLASS - 10 MODERN GRADED SCIENCE 137

The region around the nucleus where the probability of finding electrons is maximum
is called sub - shell. Now, we can co-relate the 2n2 rule with sub-shells s, p, d and f. The
main shell, its sub-shells and the maximum number of electrons present there are shown
in the table given below.

Main shell Sub-shell Total electrons
K (n = 1) 1s 2
L (n = 2) 2s, 2p 2+6=8
M (n = 3) 3s, 3p, 3d 2 + 6 + 10 = 18
N (n = 4) 4s, 4p, 4d, 4f 2 + 6 + 10 + 14 = 32
N (n = 5) 5s, 5p, 5d, 5f 2 + 6 + 10 + 14 = 32

Electronic configuration and its symbolic notation

The systematic representation for the distribution of electrons in different energy
levels of an atom is called electronic configuration. The electronic configuration of an
element is shown below.

Hydrogen Number of electron to s-orbital

The electronic Principal quantum number 1s1
configuration of hydrogen Shell number (n = 1)
is 1s1. It has only one shell, Subshell
called K-shell. K-shell
contains one s-sub-shell. electronic configuration of hydrogen

The stable electronic Number of electron to s-subshell
configuration of any atom of
any element can be obtained Principal quantum number nxe
by using certain rules and (Shell = 1, 2, 3, .......)
building up principles. One Subshell: s,p,d and f
of such principle is Aufbau
principle.

Aufbau principle 1s

Aufbau (Aufbau is a German word meaning build up) 2s 2p
principle explains a sequence of filling of various subshells by 3s 3p 3d
electrons. Aufbau principle states that "electrons occupy the 4s 4p 4d 4f
subshells of minimum energy first and then they occupy the 5s 5p 5d 5f
subshells of maximum energy." This means, electrons enter 6s 6p 6d
the subshells having the lowest energy first. The orbital will be 7s 7p
filled by electrons in the following sequence.
Fig: 7.6 Aufbau pattern for
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p atomic structure

subshells being filled

This sequence of filling electrons in various sub-shells can
be shown in the given diagram.

138 MODERN GRADED SCIENCE CLASS - 10 CLASSIFICATION OF ELEMENTS

In some cases like chromium and copper, the electronic configuration differs slightly
from the actual ones, as the completely or half filled d-sub-shell is more stable than d9 or
d4. For example,

Chromium [Cr (24)] ⇒ 1s2 2s2 2p6 3s2 3p6 3d5 4s1

Copper [Cu (29)] ⇒ 1s2 2s2 2p6 3s2 3p6 3d10 4s1

S. Name and No. of e– = No. of Electronic Distribution of electrons in different Electronic Valency
No. of e+ = neutron configuration
N. symbol of At. number shells configuration in
elements subshells
acc. to 2n2

K

1s 2s 2p 3s 3p 3d 4s 4p 4d 4f

1 Hydrogen (H) 1 0 1 1 1s2 1

2 Helium (He) 2 22 2 1s2 0

3 Lithium (Li) 3 4 2,1 2 1s2,2s1 1

4 Beryllium (Be) 4 5 2,2 22 1s2,2s2,2p1 2

5 Boron (B) 5 6 2,3 221 1s2,2s2,2p1 3

6 Carbon (C) 6 6 2,4 222 1s2,2s2,2p2 4

7 Nitrogen (N) 7 7 2,5 223 1s2,2s2,2p3 3

8 Oxygen (0) 8 8 2,6 224 1s2,2s2,2p4 2

9 Fluorine (F) 9 10 2,7 225 1s2,2s2,2p5 1

10 Neon (Ne) 10 10 2,8 226 1s2,2s2,2p6 0

11 Sodium (Na) 11 12 2,8,1 2261 1s2,2s2,2p6,3s1 1

12 Magnesium (Mg) 12 12 2,8,2 2262 1s2,2s2,2p6,3s2 2

13 Aluminium (AI) 13 14 2,8,3 22621 1s2,2s2,2p6,3s2, 3p1 3

14 Silicon (Si) 14 14 2,8,4 22622 1s2,2s2,2p6,3s2, 3p2 4

15 Phosphorus (P) 15 16 2,8,5 22623 1s2,2s2,2p6,3s2, 3p3 3,5

16 Sulphur (S) 16 16 2,8,6 22624 1s2,2s2,2p6,3s2, 3p4 2,6

17 Chlorine (CI) 17 18 2,8,7 22625 1s2,2s2,2p6,3s2, 3p5 1

18 Argon (Ar) 18 22 2,8,8 22626 1s2,2s2,2p6,3s2, 3p6 0

19 Potassium (K) 19 20 2,8,8,1 2262601 1s2,2s2,2p6,3s2, 1
3p6,4s1

20 Calcium (Ca) 20 20 2,8,8,2 2262602 1s2,2s2,2p6,3s2, 2
3p6,4s2

21 Chromium (Cr) 24 2,8,13,1 2262651 1s2,2s2,2p6,3s2, 2,6
3p6,4s1,3d5

22 Iron (Fe) 26 2,8,14,2 2262662 1s2,2s2,2p6,3s2, 2,3
3p6,4s2,3d6

23 Copper (Cu) 29 2,8,18,1 2 2 6 2 6 10 1 1s2,2s2,2p6,3s2, 1,2
3p6,4s1,3d10,

24 Silver (Ag) 49 2,8,18,18,1 2 2 6 2 6 10 2 6 10 1 1s2,2s2,2p6,3s2, 3p6, 1
4s2,3d10,4p6,4d10, 4f1

CLASSIFICATION OF ELEMENTS CLASS - 10 MODERN GRADED SCIENCE 139

Blocks of modern periodic table

The physical and the chemical properties of the elements depend on the arrangement
of the electrons in the sub-shell. According to the arrangement of electrons in the sub-shell,
the elements in the periodic table are divided into 4 blocks. They are s-block, p-block,
d-block and f-block.

s-block

The s-block includes the elements of groups IA (alkali metals) and IIA (alkali earth
metals). They are present at the left side of the periodic table. In this block, either one or
two valence electrons are being filled in the s-subshell. These elements form positive ions
by losing one or two electrons to other atoms during combination. Some examples of
s-block are Li, Na, K, Be, Mg, Ca, etc.

p-block

The p-block (13), (14), (15), (16), (17), (18) metals, metalloids, non-metals and inert
gases which are present in groups IIIA, IVA, VA, VIA, VIIA and group 0. It is present at
the right side of the modern periodic table. The elements of this block have 3, 4, 5, 6, 7
and 8 valence electrons. The valence electrons are being filled in the p-orbitals of all the
elements of group IIIA to VIIA. The elements of group 0 have completely filled p-orbitals
(ns2, np6) and are known as noble gases. Some examples of p-block are C, N, O, F, Cl, Br,
Ar, etc.

Difference between s-block and p-block elements

s-block elements p-block elements

1. The s-block elements have s-sub-shell 1. The p-block elements have p-sub-shell

as the last orbital. as the last orbital.

2. They can have only 1 or 2 electrons in 2. They can have 1 to 6 electrons in the last

the last sub-shell. sub-shell.

3. The chemical reactivity of elements 3. The chemical reactivity of elements

increases while going downwards in a decreases while going downwards in a

group. group.

4. Melting point and boiling point decrease 4. Melting point and boiling point increase

while going downward in a group. while going downward in a group.

d-block

The d-block includes the elements of sub-groups III B, IVB, VB, VIB, VIIB, VIII,
IB (groups 3 to 12) and IIB. The d-block elements are also called transitional elements
because they lie in the middle of the periodic table between s-block and p-block. All of
them are metals. The valence electrons are being filled on the d-orbital or sub-shell of all
the elements of sub-groups B and VIII. Some examples of d-block are Ag, Au, Fe, Cu, Zn.

f-block

The elements of lanthanide and actinide series are called f-block elements. They are
also called inner-transition elements because, while moving from the transition elements
of group IIIB to group IVB, we have to transit through these elements. They are 28 in

140 MODERN GRADED SCIENCE CLASS - 10 CLASSIFICATION OF ELEMENTS

number. These two series of elements are similar in chemical properties and are placed
in two rows at the bottom of the periodic table. In these elements, the f-sub-shell is
incomplete and the electrons are gradually being filled as the atomic number increases.

In the periodic table, there are 7 periods. The different numbers of elements are placed
in each period having s, p, d and f-block which are tabled below.

Periods in table No. of Elements in Blocks

1 spd f Total
2 2
3 2––– 0
4 8
5 26 – 18
6 18
7 26 – 32
32
2 6 10 –
118
2 6 10 –

2 6 10 14

2 6 10 14

Grand Total

S me Reasonable Facts

1. The elements of group IA (Li, Na, K, Rb, Cs, Fr) are known as reactive metals because
they all have a single valence electron due to which they can easily lose the single
electron to other to become stable.

2. The elements of group VIIA/17, are called halogens as they form salt by reacting with
metals.

3. In group IA/1, IIA/2 and IIIA/13 reactivity of metals increases from top to bottom. It is
because these metals are electro-positive and they lose valence electron(s) easily from
top to bottom in a group due to their increasing atomic size and decreases the nuclear
attraction to the valence shell.

4. In group VA/15, VIA/16 and VIIA/17, reactivity of elements decreases from top to
bottom. It is because they contain non-metals which are electronegative and the
tendency of gaining foreign electron(s) decreases from top to bottom in a group due
to their increasing atomic size and decreases the nuclear attraction to the valence
shell.

5. Atomic size decreases from left to right in a period. It is because of increasing valence
electrons from left to right. As the number of electrons and protons increases, the
attraction between the nucleus and valence electron also increases which makes the
last orbit compressed towards the nucleus and the atomic size decreases.

6. Argon is a noble gas. It is because argon is an octet i. e. it has 8 electrons in its last orbit.
Due to this reason, the element does not combine with others in normal conditions.

7. The elements of group 3 to 12 are called transition elements because they represent
change or transition in character from reactive metals i. e. the elements of group 1 and
2 on the left side to non-metals i. e. the elements of group 13 to 18 on the right side.

CLASSIFICATION OF ELEMENTS CLASS - 10 MODERN GRADED SCIENCE 141

8. The non-metal having a smaller atomic size is more reactive than that which has a
bigger atomic size. As non-metals have to gain electrons while making a molecule,
the smaller atomic size has more force of nucleus for it. Due to this reason, fluorine
is more reactive than chlorine as it has smaller atomic size even though both of them
have the same valency.

Things To Know

1. The systematic arrangement of elements on the basis of similarities of electronic
configuration into groups and periods is called the periodic table.

2. Mendeleev's periodic law states that ''physical and chemical properties of elements
are the periodic functions of their atomic weights''.

3. The horizontal rows of the periodic table are called periods.

4. The vertical columns of the periodic table are called groups. All the elements of a
group have similar chemical properties as they have the same valency.

5. The modern periodic table is also called the long form of the periodic table.

6. The modern periodic law states that ''the physical and the chemical properties of
elements are periodic functions of their atomic numbers''.

7. The classification of elements based on the modern periodic law is called modern
periodic table.

8. There are seven periods and 18 groups in the modern periodic table.

9. The members of group IA/1 are called alkali metals because they dissolve in water,
forming metal hydroxides or alkalis, and hydrogen gas is evolved.

10. Inert gases like helium, neon, argon, krypton, xenon and radon have zero valency
and they have no capacity to combine with other elements.

11. The atoms which contain 8 electrons in their valence shell are called octets.

12. The atoms of the same element having equal atomic number but a different mass
number are called isotopes. The nuclei of the isotopes contain equal number of
protons but a different number of neutrons.

13. Valency and atomic size determine the reactivity of elements. The elements of lower
valency are more reactive than those which have more valency. Metals with a big
atomic size and non-metals with a small atomic size are more active than others.

14. In a group from top to bottom reactivity of metals increases reactivity of non-metals
decreases.

Things To Do

1. Draw a modern periodic table on a sheet of chart paper and write the following in the
letters of varying colours in the table.

a. alkali metals b. alkaline earth metals

c. transition metals d. halogens

e. noble gases

142 MODERN GRADED SCIENCE CLASS - 10 CLASSIFICATION OF ELEMENTS

Test Yourself

1. Multiple choice questions (MCQs).

a. According to modern periodic law the properties of elements are periodic
function of their:

A. atomic number B. atomic size

C. atomic mass D. mass number

b. Alkali metals belong to:

A. p-block elements B. s-block elements

C. d-block elements D. f-block elements

c. ……… is a highly reactive element.

A. Beryllium B. Magnesium

C. Sodium D. Aluminium

d. Which one of the given elements is the least reactive?

A. fluorine B. chlorine

C. iodine D. bromine

e. The d-block elements are also called……..

A. halogens B. representative elements

C. transition elements D. alkaline earth metals

f. There are …… groups in the modern periodic table.

A. 7 B. 18 C. 15 D. 10

g. The orbital configuration of chlorine is:

A. 1s2, 2s2, 2p6, 3s2, 3p5 B. 1s2, 2s2, 2p6, 3s2, 3p5

C. 1s2, 2s2, 2p6, 3s2, 3p6 D. 1s2, 2s2, 2p6, 3s2, 3p6

h. The inert elements belong to:

A. Group I A B. Group VII

C. Zero (0) D. Group I B

2. Differentiate between:
a. Group and period
b. Short period and long period
c. s-block element and the p-block element
d. Mendeleev's periodic table and the modern periodic table

3. Give reasons.
a. Argon is an inert gas.
b. The valency of nitrogen is 3.
c. Chlorine is an active non-metal.
d. Fluorine is more reactive than chlorine.
e. Sodium is less reactive than potassium.

CLASSIFICATION OF ELEMENTS CLASS - 10 MODERN GRADED SCIENCE 143

f. The members of group IA are called alkali metals.
g. The group I elements are very active.
h. Lanthanides and actinides are kept separately in the modern periodic table.
i. Transition elements have variable valency.
j. Halogens are active non-metals.

4. Answer the following questions.
a. What is the periodic table?
b. State Mendeleev's periodic law.
c. What are the merits of Mendeleev's periodic table?
d. What are the defects of Mendeleev's periodic table?
e. State modern periodic law.
f. What are the features of the modern periodic table?
g. How is the modern periodic table superior to Mendeleev's table?
h. Why are Li, Na and K placed in the same group of the periodic table?
i. Name two alkaline earth metals.
j. What do you mean by p-block elements? Write any five examples of this block.
k. Define:

i. group ii. period

iii. periodic table iv. isotopes

v. sub-shell vi. transition element

l. What factors do the valencies of elements depend upon?

5. Diagrammatic questions

a. A part of a periodic table is given below. Study it and answer the following
questions.

IA IIA IIIA IVA VA VIA VIIA O
Periods 2 Li Be B C N O F Ne

3 Na Mg Al Si P S Cl Ar
i. Write the names of two very reactive non-metals.
ii. Sketch the atomic structure of that element which is placed in period 3 and

has valency 4.
iii. Name the most reactive metal with a suitable reason.
b. Study the given electronic configuration of the elements and answer the following
questions.
A. 2, 8, 1 B. 2,8 C. 2, 8, 7 D. 1
i. Give the names of a metal and a non-metal from above.
ii. Which one of the above elements is inert and why?
iii. Identify those elements which are placed in group VIIA and IA.

144 MODERN GRADED SCIENCE CLASS - 10 CLASSIFICATION OF ELEMENTS

c. By reference to the table, answer the following questions. Remember that in the
table, the symbols do not show the proper symbols.

Group I II III IV V VI VII O

Lithium Carbon Oxygen W Neon

A KX

BY

CZ

i. What are the valencies of oxygen, carbon and A?

ii. How many electrons are in the valence shell of W?

iii. Which is the most reactive metal among them? Why?

iv. Which is the most reactive non-metal among them? Why?

v. Name the elements W, X, Y and Z.

vi. If a metal 'M' forms a compound with oxygen and its formula is MO, what
will be the formula of its compound formed with K.

d. The electronic configuration of some elements is given below. With the help of
such electronic configurations, answer the following questions.

A = 1s2, 2s2, 2p6, 3s1 B = 1s2, 2s2, 2p6, 3s2, 3p6, 4s1

C = 1s2, 2s2, 2p5 D = 1s2, 2s2, 2p6, 3s2, 3p5

i. Write the valency, period number, group number and block of the elements
given above.

ii. Name the chemical compound and molecular formula formed between A
with D and B with C.

iii. Which element is more reactive between A or B and ii) C and D.

iv. Which element is more reactive, C or D?

Ion : electrically charged particles.
Shell : orbit around the nucleus
Periodic : repeating after a regular interval

CLASSIFICATION OF ELEMENTS CLASS - 10 MODERN GRADED SCIENCE 145

Chapter CHEMICAL REACTION

8 Total estimated periods: 7 (T 5 + P 2)

classify different types of chemical reactions.
translate chemical reactions into chemical equations.
describe the factors and catalyst of chemical reactions.

Change is the law of nature. We can notice many changes around us. A child grows
into an adult person, milk changes into curd, a glass breaks into pieces, paper burns to ash,
an iron bar gets rust and wet clothes become dry in sunlight. In the same way, burning of
wood, magnetization of iron nails, ripening of fruit, etc. are different examples of changes
in nature. These changes are classified into physical and chemical changes.

A physical change is the temporary change in which the chemical properties of the
substance are not destroyed and no new substances are formed. In this change, physical
properties of substances like colour, state, shape, size and odour may change e.g. change
of water into ice, magnetization of an iron nail, etc.

A chemical change is a process in which new substances with different properties and
composition, are formed. In a chemical change, the properties of the substances before
and after the change are completely different. For example, rusting of iron, burning of
paper and wood, ripening of fruits, etc. All the chemical changes in substances involve
chemical reactions. In this lesson, we are going to study about the types of reactions,
conditions for chemical reactions, chemical equations, etc.

Chemical reaction

Achemical reaction is a chemical change which takes place by addition, decomposition
or displacement of the atoms or molecules of the matter into new substances. All chemical
reactions are represented by chemical equations.

A chemical equation is the symbolic representation of the actual chemical reaction
in terms of equation. It may be a word equation or a formula equation. In a formula
equation, the molecular formulae of reactions and products are used. For example, zinc
reacts with sulphuric acid to produce zinc sulphate and hydrogen gas.

146 MODERN GRADED SCIENCE CLASS - 10 CHEMICAL REACTION