6. A concave lens is the lens which is thin in the middle and thick at the edges. A
concave lens diverges parallel rays of light after refraction. So, it is called a diverging
lens.
7. Optical centre is the geometrical centre of a lens. It is denoted by O. A ray of light
passing through optical centre does not deviate.
8. Focal length of a lens is the distance between optical centre and principal focus of
the lens. It is denoted by ‘f’.
9. The straight line passing through optical centre and centre of curvature is called
principal axis.
10. The ray of light passing parallel to the principal axis of a convex lens passes through
principal focus after refraction.
11. The ray of light passing through the optical centre of a convex lens passes straight
without deviation.
12. A ray of light parallel to the principle axis of a concave lens appears to be diverging
from the principal focus.
13. A ray of light passing through the optical centre of a concave lens passes straight
without bending.
14. Magnification of a lens can also be defined as the ratio of image distance to the
object distance.
15. Human eye is a spherical organ located in orbital cavity in the facial region. Each
eye consists of a biconvex lens.
16. Accommodation of eye can be defined as the ability of an eye to focus the image of
“the objects at different distances” on the retina by changing its focal length.
17. The nearest and the farthest distance that a normal eye can see clearly without any
difficulty is called range of normal eye.
18. The main causes of short-sightedness are given below:
i. Thickening of eye lens or shortening the focal length of eye lens
ii. Elongation of eye balls
19. Short-sightedness can be removed by using a concave lens of suitable thickness
(focal length) in the spectacles.
20. The main cause of long-sightedness or far-sightedness are given below:
i. Shortening of eye ball or contraction of eye ball
ii. Increase in the focal length of eye lens or decrease in thickness of th eyes lens
21 . Long-sightedness can be removed by using a convex lens of suitable power in the
spectacles.
GREEN Science (Physics) Book-10 101
Sequential General Exercise 1
1. Choose the best answer from the given alternatives.
a. The lens which is thin at the edges and thick in the middle is called ..............................
lens
concave concavoconvex
convex convexoconcave
b. A convex lens forms a virtual image when an object is placed ..............................
between F and 2F beyond 2F
between F and O at F
c. A concave lens always forms a ..............................
real image virtual image
magnified image inverted image
d. When an object is placed at F of a convex lens, the image is formed ............................
at infinity between F and 2F
beyond 2 F at 2F
e. Which of the given formula is used to calculate the power of a lens?
P = F1 P = 1f
f=p P = m1
2. Answer the following questions.
a. What is light? Name any three sources of light.
b. What are optical instruments? Give any two examples.
c. What is a lens? Name any two equipment in which lens is used.
d. Define convex lens and write its types.
e. Define concave lens and write its types.
f. Define optical centre, centre of curvature and principal focus of a lens.
g. Write any two laws of refraction through a lens.
h. Draw a ray diagram for a convex lens when an object is kept beyond 2F, at 2F and
between F and 2F. Also, write down the characteristics of the image formed.
102 GREEN Science (Physics) Book-10
i. Complete the given ray diagrams. 2F F
i. ii.
F
F
iii. iv.
F F
F
F
j. Draw a ray diagram showing the image formed by a concave lens when an object
is placed between F and 2F of the lens.
k. Define real image and virtual image.
l. Write any two uses each of convex lens and concave lens.
m. What is power of a lens? Write down its formula.
n. What is meant by magnification of a lens?
o. Define accommodation and write down normal range of vision of a human eye.
p. What is defect of vision? What are its types?
q. Define short-sightedness and write two reasons for this type of defect.
r. What is long-sightedness? Write its two causes.
s. Draw a neat figure showing:
i. myopia and its correction.
ii. hypermetropia and its correction.
3. Give reason:
a. Convex lens is called a converging lens and concave lens is called a diverging
lens.
b. Human eye is called an optical instrument.
c. Convex lens is used to correct long-sightedness.
d. Concave lens cannot be used to remove far-sightedness.
e. Convex lens cannot be used to remove short-sightedness.
GREEN Science (Physics) Book-10 103
4. Write any two differences between
a. Real image and virtual image
b. Short-sightedness and long-sightedness
c. Concave lens and convex lens
d. Object distance and image distance
5. Study the given figure and answer the following questions.
a. Name the type of defect of vision.
b. Write two causes of this defect.
c. How can we remove such type of defect?
d. Draw a ray-diagram showing correction of such type of defect.
6. Numerical Problems:
a. The focal length of a lens is + 100 cm. Calculate its power. Also, write the type of
lens. [Ans: + 1D, Convex]
b. The power of a lens is + 1D. Calculate its focal length. [Ans: 1m]
c. An object is placed 10 cm away from a convex lens. If the focal length of the lens
is 5cm, calculate the magnification. [Ans : 1]
d. The magnification produced by a lens is 5. If the height of the image is 50cm,
calculate the height of the object. [Ans: 10cm]
e. An object is placed 10cm away from a convex lens. If the magnification produced
by the lens is 0.5, calculate the image distance. [Ans: 5cm]
f. The height of the image formed by a convex lens is 40 cm and that of an object is
10 cm. Calculate the magnification produced by the lens. [Ans: 4]
104 GREEN Science (Physics) Book-10
Grid-based Exercise 2
Group ‘A’ (Knowledge Type Questions) (1 Mark Each)
1. Define convex lens with a diagram.
2. What is a concave lens ?
3. What is principal axis ?
4. What is centre of curvature ?
5. What is focal length ?
6. Define focal point.
7. What is virtual image ?
8. Name the type of lens which forms a real image.
9. What is an optical instrument ?
10. Write two types of defect of vision ?
11. What is myopia ?
12. What is far-sightedness ?
13. Name two liquids found in the human eye.
14. Which formula is used to find the fluctuation of the shape of a body ?
15. What is the far point of the human eye?
Group ‘B’ (Understanding Type Questions) (2 Marks Each)
16. Write two differences between convex lens and concave lens.
17. The power of a lens is +2D. Name the type of the lens.
18. Why is concave lens also called diverging lens?
19. Write down any two differences between short-sightedness and long-sightedness.
20. Which type of defect is found in the given diagram of the eye ? Write
with reason.
21. Write two differences between real image and virtual image.
22. Write two differences between image formed by a convex lens and image formed by
a concave lens.
23. If a man with short-sighted eye wants to read a textbook, what should be the distance
between book and the lens ? Give reason.
24. A concave lens is used to remove myopia. Why ?
25. Convex lens is called a converging lens. Why? Write with figure.
26. In which condition does a convex lens form erect and enlarged image? Show with a
ray diagram.
GREEN Science (Physics) Book-10 105
Group ‘C’ (Application Type Questions) (3 Marks Each
27. Write down three uses of convex lens.
28. Write down any three uses of concave lens.
29. An object is placed 3cm away from the optical centre of a lens of focal length 4 cm. The
image is formed at the same side of the object. Then,
i. name the type of the lens used.
ii. write two nature of the image formed.
iii. draw a neat ray diagram.
30. Study the given diagram and answer the following questions: Retina
i. What defect of vision is found in the eye ? What is
the cause of such a defect of vision ? Object
ii. Which lens is to be used to correct this defect of Image
vision?
31. The corrected diagram of an eye with a defect of vision is shown.
Draw a ray diagram of the defective eye without using the given lens.
32. State three laws of refraction of light through convex lens.
Group ‘D’ (Higher Abilities Type Questions) (4 Marks Each)
33. Draw a clear ray diagram of the image formed when an object is placed 30 cm away
from a lens having the focal length 10 cm. Calculate the magnification of the image.
34. Study the given defect of vision in the given figure and answer the following
questions: 1 +3
i. Write two causes of this defect. Retina
Image
ii. How is this defect corrected ? Redraw the diagram
showing its correction.
35. A student of last bench of a class cannot read the
letters written on the board. Which types of defect
of eye does she/he have? Draw a figure showing Object F O F
such type of defect of vision. Complete the given ray
diagram. 1+2+1
36. If a man with long-sighted eye wants to read a textbook, what should be the distance
between book and the lens ? Give reason. Draw a diagram of a short-sighted eye and
with the defect corrected. 1+1.5+1.5
37. Explain with reason that when sunlight is focused on a piece of paper with the help of a
convex lens, the paper will burn. After examining the eye of a student, a doctor suggested
him to use spectacles of power +2D and answer the following questions: 1.5+1+1.5
i. What type of defect is there in his eye?
ii. Draw a diagram to show the correction of this defect after using the spectacles.
106 GREEN Science (Physics) Book-10
UNIT Current Electricity and
6 Magnetism
Weighting Distribution Theory : 10 Practical: 3
Before You Begin
The from of energy which is produced due to continuous flow of electrons
through a conductor is called current electricity. In the present day world,
current electricity is the main source of energy. It is widely used in our day
to day life. It is used to get light, to get heat, to run engines and various
equipment in industries. Electricity is essential to operate fan, computer,
mobile phone, television, radio, electric motor, etc. Electrical energy can be
changed into different forms of energy like light energy, heat energy, sound
energy, chemical energy. Electricity is also required for electroplating,
electrorefining, electrotyping, etc. Electricity is a very important source of
energy for human beings. In this unit, we will study the effects of current
electricity, electrical equipment of daily use, electric power consumption,
transformation and its type in brief.
Learning Objectives Syllabus
After completing the study of this unit, students will be able to: • Introduction to current
electricity
i. explain the effects of current electricity with
examples. • Effects of current electricity
– Heating effect
ii. ii. introduce electrical equipment and – Lighting effect
electromagnetic equipment and describe their utility – Magnetic effect
in our daily life. • Electromagnetic equipment
iii. iii. explain safety measures that should be adopted and their utilities
while using electricity. – Electric bell
– Bicycle dynamo
iv. iv. explain the structure and types of transformer. – Generator
– Electric motor
v. v. solve simple numerical problems based on – Inverter
electric tariff and transformer. – Charger
– Transformer
• Safety measures while using
electricity
• Electric power consumption
Glossary: A dictionary of scientific/technical terms
current electricity : the form of energy which is produced due to continuous flow of electrons
through a conductor
electromagnet : the magnet made by passing electric current through a solenoid
transformer : the equipment which converts low voltage AC into high voltage AC and
vice-versa
dynamo : a device which converts mechanical energy into electrical energy
inverter : the equipment which converts AC into DC and vice-versa
GREEN Science (Physics) Book-10 107
Effects of Current Electricity
Current electricity has so many effects. We can convert electrical energy into light energy
by using bulb or tube light. We can convert electrical energy into heat energy by using an
electric heater. We can make a magnet by using electricity. Similarly, electroplating and
electrotyping can be done with the help of electricity. It shows that current electricity can
have different effects. Some of them are mentioned below:
1. Heating effect
2. Lighting effect
3. Magnetic effect
4. Chemical effect
In this unit, we will study only three effects of current electricity, viz. heating effect,
lighting effect and magnetic effect.
1. Heating Effect of Current Electricity
When we pass electric current though a conductor having a high resistance, it becomes
hot and radiates heat energy. Such type of effect of current electricity is called heating
effect. Heating effect of current electricity is widely used in our daily life. We use electric
heater to make our home warm. Heating devices are also used to boil water, to cook food,
to press clothes and so on. Similarly, we use immersion rod to heat water for bathing in
winter. Some common devices that convert electrical energy into heat energy are given
below:
Fig.
6.1 Electric heater Electric kettle Immersion rod
Electric iron
In heating devices like iron, heater,
immersion rod, etc. nichrome wire is used Do You Know
as a heating element. Nichrome wire is an
alloy of nickel and chromium. It has a very Heating element is a wire having high
high resistance. So it becomes very hot while resistance which converts electrical energy
passing electricity and radiates heat energy. into heat energy. It is used in heating
devices, e.g. nichrome wire.
Nichrome wire does not react with oxygen
when heated upto 900°C. Therefore, the heating element made of nichrome wire is more
durable than any other heating element.
108 GREEN Science (Physics) Book-10
2. Lighting Effect of Current Electricity
When we pass electric current through the filament (made of tungsten) of an electric bulb,
the filament becomes very hot and emits light. Such type of effect of electric current is
called lighting effect of current electricity.
Lighting devices like filament lamp, fluorescent lamp, LED bulb, etc. are based on the
principle of lighting effect of current electricity.
a. Filament lamp
An electric lamp in which filament is used to get light is called filament lamp. The filament
of the bulb is made of tungsten. The coil of tungsten is very thin. Its melting point is about
3400° C. The resistance of filament is very high. It becomes white hot while passing
electricity and emits visible light. The temperature of the filament reaches about 2900°C.
Filament lamp converts 10% of electrical energy into light energy and 90% into heat
energy. The life span of a filament lamp is about 1000 hours.
When hot filament is exposed to air, it gets oxidized. As a result, the filament gets damaged.
Therefore, a filament lamp is filled with inert gases like nitrogen, argon, neon, or made
vacuum, etc. to prevent the oxidation of filament.
Inert gas Filament
Support wires
Glass mount
Screw thread contactFig.
Insulation
6.2 Electrical foot contact
Structure of a filament lamp
Activity 1
Take a filament lamp and study its structure.
Draw a neat and labelled figure of a filament bulb.
b. Fluorescent lamp
Fluorescent lamp is a tubular electric lamp having a coating of fluorescent material on
its inner surface and containing mercury vapour. The process of emission of light in a
fluorescent lamp differs from that in a filament lamp. In a fluorescent lamp, two electrodes
(one on either side of the tube) are kept instead of filament. There is mercury vapour
inside the fluorescent lamp.
GREEN Science (Physics) Book-10 109
Electrode coil Glass tube
Aluminium cap Argon/Krypton atoms
Fig.Cathode shieldFluorescent coating
Fig.
6.3 Glass stem Liquid mercury
Structure of a fluorescent lamp
Fluorescent lamp converts 30% electrical energy into light
energy and 70% of electrical energy into heat energy. The
average life span of fluorescent lamp is 3000 hours. When
current flows through electrodes, electrons flow from one
electrodes to another through mercury vapour and mercury
atoms collide with electrons. Then, it produces invisible ultra-
violet rays. These rays fall on the inner wall of the fluorescent
lamp coated with fluorescent powder and visible light is 6.4
produced. In this way, fluorescent lamp produces light. The
colour of the light thus emitted can be changed by changing CFL
the colour of flourescent powder. Now-a-days, fluorescent lamps are replaced by CFL
(Compact Fluorescent Lamp). It converts 90% of electrical energy into light energy.
Differences between Filament lamp and Fluorescent lamp
Filament lamp Fluorescent lamp
1. Filament is used. 1. Fluorescent power is used.
2. Its life span is about 1000 hours. 2. Its life span is about 3000 hours.
3. It is filled with inert gases. 3. It is filled with mercury vapour.
4. It converts only 10% of electrical 4. It converts 30% of electrical energy
energy into light energy. into light energy.
c. LED lamp Fig.
LED lamp is an electrical device having diode that emits a bright 6.5
light. LED stands for light emitting diode. A diode is an electrical
component with two terminals that conduct electricity in only one LED lamp
direction. When electricity is passed, the diode emits a bright light
around the small bulb.
LED lamps are upto 80% more efficient than traditional lighting
devices. LED lamp converts 90% of electrical energy into light
energy. LED lamp consumes less energy, has smaller size and is
stronger that filament bulb. The life span of LED lamp is about
110 GREEN Science (Physics) Book-10
60,000 hours. LED lamps are used in houses, offices, as head lamp of automobiles, camera
flashes, traffic signals, medical devices, etc.
3. Magnetic Effect of Current Electricity
When electric current is passed through a wire, magnetic field is produced around the
wire. Such type of effect is called magnetic effect of current electricity. In modern days,
magnetic effect of current electricity is highly useful. The magnet made by passing
electricity through a solenoid is called electromagnet. It is used in electromagnetic
equipment like loudspeaker, microphone, radio, television, etc. Generally, electricity is
produced by using electromagnet.
+– Do You Know
Battery
In 1820 AD, the magnetic effect of current
Fig. electricity was discovered by the scientist
Fig. Hans Christian Oersted.
6.6
Electromagnet
Electric bell
The electromagnetic equipment which converts electrical energy into sound energy is
called electric bell. It is operated with the help of electromagnet. The bell rings when the
temporary electromagnet attracts the armature of the electric bell.
Push
Armature
Spring
U shaped
electromagnet
Contact adjustment
screw
Hammer
Gong
6.7
Structure of an electric bell
Electric bell is fixed to the board of wood or plastic. Electric circuit is completed on
pressing the switch of the bell and current flows through the coil of electromagnet. The
electromagnet attracts the armature towards it. As a result, the hammer fitted to armature
GREEN Science (Physics) Book-10 111
Fig. Fig.hits the gong and sound is produced. When the hammer hits the gong, electric circuit
breaks and the armature comes back to the original position. In this condition, the
electromagnet loses its magnetism. But when the armature comes back, electric circuit
gets completed and above process repeats once again. When this process continues, a
continuous ringing of bell is heard on pressing the switch.
Use of electrical bell
Electric bell is commonly used in house as door bell, schools, offices, telephone, etc.
Bicycle dynamo
Bicycle dynamo is an electromagnetic device which converts kinetic energy into electrical
energy. It produces electricity in a small amount. A dynamo is used in a bicycle to light
the bulb by producing electricity.
Do You Know
Bicycle dynamo works on the principle
of electromagnetic induction, i.e. when a
conductor is moved perpendicular to the
magnetic field, current is induced in the
6.8 conductor.
Bicycle dynamo
Inside a dynamo, a permanent magnet and a coil of enamel coated wire are used. An
armature is connected to the dynamo which rotates the magnet due to the motion of
bicycle tyre. When the magnet rotates, the magnetic flux linked to the coil changes and
current is induced in the coil which is wrapped around a soft iron core. The current thus
induced is used to light the bulb. The brightness of the bulb depends on the speed of
rotation of the tyre. The brightness of the bulb can be increased by increasing the speed of
rotation of the bicycle tyre.
Rotation of magnet
Dynamo body Outer coils of wire
Permanent magnet
NS
6.9 Electrical output
Bicycle dynamo (Internal structure)
112 GREEN Science (Physics) Book-10
Activity 2
Take a bicycle with dynamo.
Connect the head of the dynamo to the bicycle
tyre.
Rotate the bicycle tyre slowly and observe the
brightness of the bulb.
Now, increase the speed of rotation and observe Fig. Fig.
the brightness of the bulb.
Let the bicycle tyre come to rest. Does the bulb
glow? Why? 6.10
Write down the conclusion of this activity.
You will observe that the brightness of the bulb increases on increasing the speed of
rotation of the tyre and decreases on decreasing the speed of rotation. Similarly, the
bulb glows until there is motion in the tyre.
Activity 3
Take an empty matchbox and make a coil of insulated copper wire around it.
Connect two ends of the wire to the galvanometer.
Now, insert a bar magnet in the matchbox and move it up and down.
What do you observe? Can you see deflection in the needle of galvanometer?
Now, increase the speed of movement of the magnet and observe deflection in the
needle of galvanometer.
What is this process called? Discuss in your classroom.
Generator Generator
The electromagnetic equipment which produces
electricity in a large scale is called a generator. An
electromagnet is used in a generator instead of a
permanent magnet. When the turbine of the generator
is rotated at a high speed with an external force, the
rotor with electromagnet gets rotated. Due to this, the
magnetic flux linked with the coil changes resulting
in induction of electric current.
Methods of increasing the amount of induced current 6.11
in a dynamo or generator are as follows:
1. increasing the speed of rotation
2. decreasing the distance between the coil and the magnet
3. increasing the strength of magnetic field
4. increasing the number of turns in the coil
5. using soft iron core in the solenoid
GREEN Science (Physics) Book-10 113
Difference between AC and DC DC (Direct Current)
AC (Alternating Current) The current that dos not change its
polarity and magnitude at a certain
1. The current that changes its polarity 1. time interval is called DC (Direct
and magnitude at a certain time current).
interval is called AC (Alternating
current). It is obtained from cell and battery.
2. It is obtained from dynamo and 2.
generator.
O
O Time
Time
Electric motor Do You Know
The electromagnetic device which converts The frequency of the current distributed in
electrical energy into mechanical (kinetic) Kanchanpur district is 50 Hz means that
energy is called electric motor. It is used in the polarity of the current changes at the
tape recorders, electric fans, mixer grinders, rate of 50 times per second.
computers, washing machines, CD players,
etc.
Coil rotates clockwise
Magnetic field
NS
Brushes carry current Commutator
to commutator reverses current
Electric current
Fig.
6.12
Working mechanism of electric motor
114 GREEN Science (Physics) Book-10
An electric motor works on the principle of motor
effect which states that, "when a rectangular coil is
placed in a magnetic field and a current is passed
through it, a twisting force acts on the coil which
rotates it continuously.”
6.13Fig. Fig. Electric motor
Differences between Electric motor and Generator
Electric motor Generator
1. It converts electrical energy into 1. It converts mechanical energy into
mechanical energy. electrical energy.
2. It works on the principle of motor 2. It works on the principle of
effect. electromagnetic induction.
Inverter
In houses or offices, we can operate electric equipment 6.14
during load shedding. How is it possible to operate
these equipment? It is possible due to inverter. The
electronic equipment which converts alternating
current (AC) into direct current (DC) and direct current
(DC) into alternating current (AC) is called inverter. It
is a very useful device for developing countries.
During the supply of electricity, the inverter converts Inverter
alternating current into direct current and stores electrical energy in the battery. When
the main AC supply is obstructed, the inverter again converts direct current (DC) into
alternating current (AC) and the electric appliances can be operated. Therefore, inverter
is a very useful alternative source of electricity at the time of load shedding.
Charger
The equipment which is used to recharge a battery or a device with rechargeable battery is
called a charger. It is used to recharge the battery of mobile phone, torchlight, automobile, etc.
Fig.
6.15 Battery charger
Mobile charger
GREEN Science (Physics) Book-10 115
A battery charger forces an electric current into the rechargeable battery. A simple battery
charger supplies a constant DC to a battery which is kept for recharging. Now-a-days,
battery chargers have a cut-off system to stop the supply of electricity when the battery is
fully charged. We can find a variety of battery chargers in the market.
AC Adapter
An Ac adapter is a small electric device that changes
household voltage of AC into low voltage DC. It is
used to run radio and other electrical devices that
need low voltage DC.
Fig.
Solar cell Fig. 6.16
AC adapter
Solar cell is a device that converts sunlight
into electricity by the voltaic effect. A solar
cell is an example of photovoltaic device.
The device that generates voltage when
exposed to sunlight is called photovoltaic
device. This device was discovered by
Alexander Edmond Becquerel in 1839
AD. The major component of the solar
cell which is used to convert sunlight into
electricity is called solar module. It mainly
consists of semi-conductors (mostly 6.17
silicon crystal) which is laminated into
n-type and p-type layers. These layers are Solar cell
kept one after another. When light strikes these crystals, it induces photovoltaic effect and
electricity is produced.
Transformer Fig.
The equipment which is used to increase or Transformer
decrease the alternating electromotive force
or voltage (AC) without changing the power
is called transformer. We can generate the
voltage required by using transformer and
can be used whenever required. Similarly,
the frequency of the current can be changed
by changing magnetic lines of force.
Therefore, transformer is widely used in
various electric and electronic equipment
like trolly bus, radio, television, record 6.18
player, factories and so on.
116 GREEN Science (Physics) Book-10
Types of transformer
On the basis of structure and use, there are two types of transformer. They are as follows:
1. Step-down transformer 2. Step-up transformer
1. Step-down transformer
This type of transformer decreases the voltage of output current the voltage of input
current. The transformer which changes high voltage AC into low voltage AC is called
step-down transformer. This type of transformer decreases the alternating e.m.f. In a step
down transformer, the number of turns in the secondary coil is less than that in primary
coil. Step up transformer is used in radio, cassette player, television, etc.
Primary coil Secondary coil
1000 turns 500 turns
InputFig. Fig. Output
440 V 220 V
Step-down transformer
6.19
Step-up transformer
This type of transformer increases the output voltage compared to the input voltage.
The transformer which changes low voltage AC into high voltage AC is called step-up
transformer. The number of turns in secondary coil in a step-up transformer is more than
that in the primary coil. Step-up transformer is used in hydropower stations to transmit
electricity through overhead wires, television, X-ray tubes, etc. to produce high voltage.
Input500 turns 1000 turnOs utput
220 V 440 V
Secondary coil
Primary coil Step-up transformer
6.20
Laminated core, primary winding and secondary winding are the major components
of a transformer. The core of a transformer is made by combining numerous U-shaped
iron sheets. These iron sheets are laminated with screws. The core of a transformer is
laminated to reduce the loss of electrical energy due to the development of eddy current.
The wire of the coil of the transformer is also coated with enamel. The number of turns in
coils helps to increase or decrease the voltage (AC).
GREEN Science (Physics) Book-10 117
There are two types of coils in the transformer. They are primary coil and secondary
coil. Similarly, the number of turns in the primary coil is called primary winding and
the number of turns in the secondary coil is called secondary winding. By increasing
or decreasing the number of turns in the secondary coil of a transformer, the secondary
voltage can be increased or decreased.
The input voltage of a transformer is called primary voltage and the output voltage of a
transformer is called secondary voltage. According to requirements, secondary voltage
can be obtained by increasing or decreasing the number of turns in the secondary coil.
Following formula is used to calculate the number of turns in the secondary coil.
Secondary voltage (V2) = No. of turns in secondary coil (n2)
Primary voltage (V1) No. of turns in primary coil (n1)
In short, Do You Know
V2 = n2 The amount of DC (voltage) does not
V1 n1 change. So transformer cannot change the
e.m.f. of a dry cell.
or, n2 V1 = n1V2
A transformer is constructed by calculating primary voltage, secondary voltage, number
of turns in the primary coil and no. of turns in the secondary coil.
Solved Numerical: 1
In a transformer, the number of turns in the primary coil is 1000 and that in the secondary
coil is 2500. If the primary voltage is 440 V, calculate the secondary voltage. What is the
type of transformer? Why?
Solution:
No. of turns in primary coil (n1) = 1000
No. of turns in secondary coil (n2) = 2500
Primary voltage (V1) = 440V
Secondary voltage (V2) = ?
According to the formula
V2 n1 = V1n2
V2 = V1 n2
n1
or, V2 = 440 × 2500
1000
= 1100V
\ Secondary voltage (V2) = 1100V.
The type of transformer is step-up because secondary voltage is more than the primary
voltage.
118 GREEN Science (Physics) Book-10
Solved Numerical: 2
In a transformer, the number of turns in the primary coil is 100 times less than that in the
secondary coil. If the secondary voltage is 33000V, calculate the primary voltage.
Solution:
Let no. of turns in primary coil (n1) be x
Then, no. of turns in secondary coil (n2) = 100x
Secondary voltage (V2) = 33000V
Primary voltage (V1) = ?
According to formula,
n2 V1 = n1V2
V1 = n1 V2
n2
or, = x × 33000
100x
= 330V
\ Primary voltage (V1) = 330V.
Safety measures while using electricity
Electricity is the most essential form of energy in the present day world. We cannot
imagine modern life without electricity. However, we should be very careful while using
electricity. Misuse or mishandling of electricity may be fatal and it causes a huge loss of
life and property. The safety measures that should be adopted while using electricity are
given below.
1. We should use electric wires and electric appliances of high quality.
2. We should use the wires of proper amperage and proper insulation.
3. Naked and connected wires should be covered properly with insulating tape.
4. Switch should always be connected with live wire.
5. Fuse should always be connected with live wire.
6. Wiring should be done only in dry places.
7. We should replace damaged switch, plug and electric appliances.
8. We should not touch naked wires.
9. We should not touch switches, plugs and electric appliances with wet hands.
10. We should use insulated gloves (rubber gloves) and shoes while working with
electricity.
11. Electric appliances should be earthed.
GREEN Science (Physics) Book-10 119
12. We should use the fuse of proper rating.
13. We should use MCB to protect our house/office from short-circuiting.
14. The connection of switches, plugs and sockets should be strong.
15. The colour code of wires should be followed in household wiring.
Electric power consumption
The electrical energy consumed in our houses and offices is measured in unit or kilo-watt-
hour (kWh). Electric power consumption can be defined as the rate at which electrical energy
is consumed while operating electric appliances. The total electrical power consumed can
be found by reading the kWh meter provided by Nepal Electricity Authority. Kilowatt hour
meter is the electric equipment that measures electricity consumed in kilowatt hour or
unit. One kilowatt hour is the amount of electricity consumed by an appliance of 1000 W
or 1 kilowatt when it is operated for 1 hour.
1 unit electricity consumption = 1 kilowatt hour
= 1 kW × 1 hr
= 1000 W × 60 × 60 s
= 1000 J/s × 60 × 60 s
= 3.6 × 106 J
Following formula is used to calculate electric power consumption
Electrical power consumption = P × n × t
Where, P = power of electrical appliance
n = number of appliances
t = time in hours
Following points should be remembered while calculating electric bill or tariff.
1. If the power of electric appliances is given, we should convert it into kilowatt (kW) by
dividing by 1000. [ 1kW = 1000 W]
2. The electric power (in kW) should be multiplied by time (in hours) and number of
electrical appliances.
3. The electric power consumed in kilowatt hour should be written in unit.
Solved Numerical: 3
In a house, 5 LED bulbs of 13 W each, are used for 5 hours daily, 1 TV of 35 W is used for
6 hours daily and an iron of 1200 W is used for 5 hours daily. Calculate the total electrical
energy consumed in 1 month. If the cost of 1 unit is Rs. 9, calculate the total tariff of
electricity.
120 GREEN Science (Physics) Book-10
Solution:
Electricity consumed by LED bulbs in 1 day = P × n × t
= 13 5× 5
1000
= 0.325 kWh
Electricity consumed by TV in 1 day = P × n × t
= 35 × 1 × 6
1000
= 0.21 kWh
Electricity consumed by iron in 1 day = P × n × t
= 1200 × 1 × 5
1000
= 6 kWh
Total electricity consumed in 1 day = (0. 325 + 0.21 + 6) kWh
= 6.535 kWh
\ Total electricity consumed in 1 month = 30 × 6.535 kWh
= 196.05 unit
Now,
Total cost (tariff) of electricity = Rs. 9 × 196.05
= Rs. 1764.45
Differences between step-down transformer and step-up transformer
Step-down transformer Step-up transformer
1. It converts high voltage AC into low 1. It converts low voltage AC into high
voltage AC. voltage AC.
2. The no. of turns in secondary coil is 2 The no. of turns in secondary coil is
less than that in primary coil. more than that in primary coil.
Activity 4
Visit a nearby electrical workshop.
Request the proprietor to demonstrate the structure of electric motor, transformer,
dynamo, etc.
GREEN Science (Physics) Book-10 121
Key Concepts
1. The from of energy which is produced due to continuous flow of electrons through
a conductor is called current electricity.
2. Electricity is essential to operate fan, computer, mobile phone, television, radio,
electric motor, etc. Electrical energy can be changed into different forms of energy
like light energy, heat energy, sound energy, chemical energy.
3. When we pass electric current though a conductor having high resistance, it
becomes hot and radiates heat energy. Such type of effect of current electricity is
called heating effect.
4. Heating element is a wire having high resistance which converts electrical energy
into heat energy. It is used in heating devices, e.g. nichrome wire.
5. When we pass electric current through the filament (made of tungsten) of an electric
bulb, the filament becomes very hot and emits light. Such type of effect of electric
current is called lighting effect of current electricity.
6. When electric current is passed through a wire, magnetic field is produced around
the wire. Such type of effect is called magnetic effect of current electricity.
7. The electromagnetic equipment which converts electrical energy into sound energy
is called electric bell.
8. Bicycle dynamo is an electromagnetic device which converts kinetic energy into
electrical energy.
9. Bicycle dynamo works on the principle of electromagnetic induction, i.e. when a
conductor is moved perpendicular to the magnetic field, current is induced in the
conductor.
10. The electromagnetic equipment which produces electricity in a large scale is called
a generator.
11. The electromagnetic device which converts electrical energy into mechanical
(kinetic) energy is called electric motor.
12. An electric motor works on the principle of motor effect which states that, “when
a rectangular coil is placed in a magnetic field and a current is passed through it, a
twisting force acts on the coil which rotates it continuously.”
13. The electronic equipment which converts alternating current (AC) into direct
current (DC) and direct current (DC) into alternating current (AC) is called inverter.
14. The equipment which is used to recharge a battery or a device with rechargeable
battery is called a charger.
15. The equipment which is used to increase or decrease the alternating electromotive
force or voltage (AC) without changing the power is called transformer.
16. The transformer which changes high voltage AC into low voltage AC is called step-
down transformer.
17. The transformer which changes low voltage AC into high voltage AC is called step-
up transformer.
18. By increasing or decreasing the number of turns in the secondary coil of a
transformer, the secondary voltage can be increased or decreased.
19. Misuse or mishandling of electricity may be fatal and it causes a huge loss of life
and property.
20. Fuse should always be connected with live wire.
122 GREEN Science (Physics) Book-10
21. We should use MCB to protect our house/office from short-circuiting.
22v. The electrical energy consumed in our houses and offices is measured in unit or kilo-
watt-hour (kWh).
Sequential General Exercise 1
1. Choose the best answer from the given alternatives.
a. Which of the following equipment is based on heating effect of current electricity?
filament lamp CFL heater dynamo
b. The device that produces electricity in a large scale is called ..............................
dynamo generator transformer inverter
c. Which of the following is used as a heating element?
iron copper tungsten nichrome
d. The average life span of a filament lamp is ..............................
1000 hours 3000 hours 1000 days 300 days
e. Which of the given materials is used for laminating the core of a transformer?
shellac enamel tape rubber
2. Answer the following questions.
a. What is current electricity?
b. Write any four effects of current electricity.
c. What is meant by heating effect of current electricity?
d. Name any two appliances that are based on heating effect of current electricity.
e. What is heating element ? What is it made of?
f. What is lighting effect of current electricity?
g. What is filament lamp? Write a short note on it.
h. What is filament made of?
i. What is fluorescent lamp? Describe its structure in brief.
j. Write down the use of electric bell. Draw a neat and labelled figure of an electric
bell.
k. Define dynamo and generator.
GREEN Science (Physics) Book-10 123
l. Write short note on:
i. electric motor ii. inverter iii. charger
m. What is a transformer? Name its types.
n. Write any five safety measures that should be adopted while using electricity.
o. What is electric power consumption? Define 1 kWh.
3. Write down the function of filament in a filament lamp.
4. Write down the full form of CFL. The use of CFL in place of filament lamp helps
to reduce load shedding. Justify this statement.
5. Describe the working mechanism of an electric bell with a neat figure.
6. How does a dynamo work? Explain.
7. Write any three methods of increasing the amount of current produced by a
dynamo or generator.
8. Describe the structure of a transformer with a neat and labelled figure.
9. Differentiate between:
a. AC and DC
b. Filament lamp and fluorescent lamp
c. Dynamo and generator
d. Electricity obtained from battery and electricity obtained from generator
e. Step-down transformer and step-up transformer
f. Inverter and charger
g. Tungsten and nichrome
10. Give reason:
a. Inert gases are filled inside filament lamp.
b. Nichrome wire is used as a heating element.
c. Fluorescent lamp of 25 W gives more light than the filament lamp of 50 W.
d. A filament lamp is dimmer than a flourescent lamp of the same power.
e. The core of a transformer is laminated.
f. The number of turns in primary coil and secondary coil of a transformer is never
made equal.
g. Load shedding can be reduced by using CFL.
h. Laminated copper wire is used to make an electromagnet.
11. The use of alternating current would be limited in the absence of transformer.
Justify this statement.
124 GREEN Science (Physics) Book-10
12. Numerical problems:
a. A transformer consists of 770 turns in primary coil. If the primary voltage is 220V
and secondary voltage is 110V, calculate the number of turns in secondary coil.
[Ans: 385 turns]
b. In a transformer, the number of turns in secondary coil is three times less than that
in the primary coil. If the primary voltage is 220V, find the secondary voltage.
[Ans : 73.33V]
c. Study the given figure and answer the following questions.
440 V
220 V
Primary coil 500 turns
i. What is the type of transformer? Why?
ii. Calculate the number of turns in primary coil. [Ans: 1000 turns]
d. The number of turns in primary coil of a transformer is 150 times more than
that in the secondary coil. If the secondary voltage is 220V, calculate the primary
voltage. [Ans : 33000V]
e. What will be the cost of one day for using a heater of 1000 W for 10 hours and 4
bulbs of 50 W each for 15 hours. The cost of one unit is Rs. 9.50. [Ans: Rs. 123.5]
f. In a hotel, 100 bulbs each of 60W are used for 6 hours daily and 40 fans of 50W
each are used for 10 hours daily. Calculate the total tariff in 2 months if the cost
of 1 unit is Rs. 9.50. [Ans : Rs. 31920]
Grid-based Exercise 2
Group ‘A’ (Knowledge Type Questions) (1 Mark Each)
1. Define alternating current.
2. Define direct current.
3. What is effect of current electricity?
4. What is heating element?
5. What is lighting effect of current electricity?
6. What is a filament?
7. What is electromagnetic induction ?
8. What is motor effect?
9. What is a transformer? Name the types of transformer.
10. What is electric motor?
11. What is inverter?
12. What is a charger?
GREEN Science (Physics) Book-10 125
13. Define one unit of electricity.
14. What is short circuit?
15. Write down the full form of MCB.
Group ‘B’ (Understanding Type Questions) (2 Marks Each)
16. What is meant by the statement that the frequency of the electricity distributed in
Pokhara is 50 Hz?
17. Write any two differences between heating element and filament.
18. Bulbs are connected in parallel in household wiring. Why ?
19. Write any two differences between dynamo and generator.
20. Fuse is always connected to the live line. Why ?
21. Write any two differences between filament lamp and fluorescent lamp.
22. Nichrome wire is used as a heating element. Why ?
23. Write any two differences between step-up transformer and step-down transformer.
24. Tungsten wire is not used in electric heater. Why ?
25. The number of turns in the primary coil and the secondary coil of a transformer is
never made equal. Why ?
Group ‘C’ (Application Type Questions) (3 Marks Each)
26. How are bulbs connected in the domestic wiring? Write down the three advantages
of such type of connection.
27. Electromagnet is widely used in electric appliances. Write any three reasons.
28. How is electric current induced from the bicycle dynamo? Write in brief with a neat
diagram.
29. Write any three ways of increasing electricity produced from a generator.
30. Draw a diagram of a step-up transformer and write its utility.
Group ‘D’ (Higher Abilities Type Questions) (4 Marks Each)
31. Describe the working mechanism of an electric bell with a figure.
32. Describe the structure of a step -down transformer with a labelled figure.
33. Draw a neat and labelled figure showing the structure of a filament lamp.
34. What happens when oxygen gas is used into the filament bulb? Two irons of 750 W
each are used 2 hours in a week. 10 tube lights of 20 W each are used in a house for 5
hours daily, calculate the bill of one month for the electricity with the rate of Rs. 7.30
per unit. 1 +3
35. The number of turns in the primary winding of a certain transformer is 150 times
more than that in the secondary winding. Calculate the input e.m.f. in the primary
winding if the e.m.f. generated in the secondary winding is 220V AC.
36. A current of 6.81 A flows when an electric heater is connected to 220 V AC line. If the
heater is run for 4 hours in a week, calculate the cost of electricity in two months. The
cost of one 2 kWh is Rs. 15.00.
126 GREEN Science (Physics) Book-10
Chemistry
UNIT Classification of
7 Elements
Weighting Distribution Theory : 4 Practical: 0
Before You Begin
An element is the purest from of matter which is made up of similar
type of atoms. Scientists have discovered 118 elements so far. We have
studied this fact in class 9. About 150 years ago, chemists discovered
many new elements having different physical and chemical
properties. Thereafter, the study of each element became difficult.
To make the study of these elements fast and easy, chemists felt the
necessity of grouping of known elements on the basis of similarities
and differences. This process is called classification of elements. So,
classification of elements is the grouping of elements on the basis of
their similarities and differences.
After classification, chemists arranged elements in the form of a table
on the basis of their characteristics which is known as periodic table.
The table in which elements are kept different groups on the basis
of characteristics is called periodic table. In this unit, we will study
about classification of elements in brief.
Learning Objectives Syllabus
After completing the study of this unit, students will be able to:
i. state periodic laws. • Mendeleev's periodic table
ii. explain the characteristics of the elements kept in • Modern periodic table
modern periodic table.
• Classification of elements in
iii. describe chemical reactivity of elements. periodic table
• Electronic configuration of
elements based on sub-shells
• Chemical reactivity of
elements
Glossary: A dictionary of scientific/technical terms
element : a pure substance made of only one types of atoms
periodic table : the table is which elements are classified on the basis of similarities and
periods differences
groups : the horizontal rows of elements in the periodic table
inert : the vertical columns of elements in the periodic table
halogens : neutral, inactive
: things which are used to prepare salts
GREEN Science (Chemistry) Book-10 127
Fig.Mendeleev's Periodic Table
Dmitri Mendeleev studied the properties of 63 known elements and their compounds. He
arranged elements into horizontal rows (periods) and vertical columns (groups) on the
basis of increasing atomic weights.
7.1
Mendeleev's Periodic Table
Mendeleev's periodic law states that, "The physical and chemical properties of elements
are a periodic function of their atomic weights." He felt the existence of some undiscovered
elements and he left gaps for them in the periodic table. It made discovery of new elements
easier. There were many demerits in his periodic table. He could not arrange hydrogen
properly. He kept highly reactive metals and less reactive metals in the same group. There
is no place for inert gases, lanthanides and actinides. However, Mendeleev's periodic
table was the first scientific and systematic study of elements.
In Mendeleev's periodic table, elements with similar properties are kept in the same
group and those with gradual change in properties are kept in the same period. The half
of the elements of periods 4, 5 and 6 are kept in upper left corner of the box and rest of the
elements are kept in the lower right corner of the box.
128 GREEN Science (Chemistry) Book-10
Do You Know
Mendeleev's classification of elements was
the first scientific study of the elements.
He classified elements into groups and
periods in the form of a table which is
known as Mendeleev's periodic table.
Features/Merits of Mendeleev's Periodic Table
1. Mendeleev made the study of elements easy and systematic by arranging the known
elements into groups and periods on the basis of characteristics.
2. Mendeleev left gaps for some undiscovered elements in his periodic table. It helped
in the discovery of new elements.
3. Mendeleev's periodic table helped to correct the atomic weights of some elements
like gold (Au), platinum (Pt), uranium (U), etc.
Defects/Demerits of Mendeleev's Periodic Table
1. The position of hydrogen in Mendeleev's periodic table is not clear because it can be
placed in group 1 along with alkali metals and in group 17 along with halogens.
In Mendeleev's periodic table, hydrogen is placed with alkali metals of group 1 but it
can also be kept with halogens of group 17.
Do You Know
Hydrogen is a non-metal but it is place at
the top of alkali metals.
2. In Mendeleev's period table, highly reactive metals like Li, Na and K and less reactive
elements like Cu, Ag and Au are kept in the same group. These two types of elements
differ in many features.
3. Some elements like cobalt (Co) and Nickel (Ni) do not obey Mendeleev's periodic
rule. The atomic weight of Cobalt is more (i.e. 58.9) than that of Nickel (58.6) but
Nickel is placed before Cobalt.
4. Noble gases or inert gases are absent in Mendeleev's periodic table.
5. There is no separate place for isotopes in Mendeleev's periodic table.
GREEN Science (Chemistry) Book-10 129
Modern Periodic Table18/0
13 14 15 16 17
7.2
Fig. Modern periodic tableModern Periodic Table9 10 11 12
130 GREEN Science (Chemistry) Book-1078
4 56
3 Lanthanides
Actinides
Fig. 1
1
3 5 6 7
2 4
2
Many chemists studied Mendeleev's periodic table and they tried to remove the defects of
Mendeleev's periodic table. In 1913 AD, scientist Henery Moseley designed a new
periodic rule which is known as modern periodic rule.
Modern periodic rule states that, "The
physical and chemical properties of elements Do You Know
are a periodic function of their atomic The vertical columns of elements in the
numbers". Then they placed elements in periodic table are called groups and the
the modern periodic table on the basis horizontal rows are called periods.
of increasing atomic numbers and found
that elements having the same physical The periodic table obtained after
properties fall one after another in the same arranging elements on the basis of
group, i.e. vertical column. The elements increasing atomic numbers is called
having gradual change in properties were in modern periodic table.
the same period, i.e. horizontal row. Modern
periodic rule corrected many defects found in the Mendeleev's period table.
Characteristics of Modern Periodic Table
1. There are seven periods, i.e. horizontal rows in Modern periodic table
Period First Second Third Fourth Fifth Sixth Seventh
No. of 2 8 8 18 18 32 26
elements
Form of very short short long long very long but
period short long incomplete
2. There are 18 groups, i.e. vertical columns in Modern periodic table. Group 18 is also
called zero (0) group in which inert gases or noble gases are placed.
3. The elements having valency zero (0) are kept in extremely right side of modern
periodic table.
4. Ten elements between group 3 and group 12 are placed between reactive metals and
non-metals. These elements are called transition elements. These elements are also
called d-Block elements.
5. There is separate place for Lanthanides and Actinides at the bottom of modern
periodic table. These elements are called f-Block elements.
The 14 elements from atomic number Do You Know
58 to 71 after Lanthanum (La) are called
Lanthanides. Similarly, the 14 elements Lanthanides and Actinides are called
from atomic number 90 to 103 after inner-transition elements.
Actinium (Ac) are called Actinides.
6. There is a separate place for highly reactive metals and less reactive metals.
GREEN Science (Chemistry) Book-10 131
Differences between Mendeleev's Periodic table and Modern periodic table
Mendeleev's Periodic Table Modern Periodic Table
1. Elements are arranged on the basis of 1. Elements are arranged on the basis of
increasing atomic weights. increasing atomic numbers.
2. There are eight vertical columns. 2. There are eighteen vertical columns.
3. There is no place for inert gases, 3. There is a separate place for inert gases,
lanthanides and actinides. lanthanides and actinides.
4. There is no place for isotopes. 4. Isotopes do not need separate place
due to the periodic rule.
Do You Know
Isotopes are the elements having the same atomic number but having different
atomic mass. For example, hydrogen (H) has three isotopes. They are
1 2 3
i. 1H (Protium) ii. 1H (Dueterium) iii. 1H (Tritium)
Groups
Groups in the modern periodic table are the vertical columns of the elements. There are
18 groups of elements in the modern periodic table. Elements having similar properties
are kept in the same group. All the elements of the same group have same number of
electrons in their valence shells.
Periods
Periods are the horizontal rows of elements in the modern periodic table. There are seven
periods in the modern periodic table. All the elements of the same period have equal
number shell in their atoms. On the basis of number of elements, periods are divided into
four types as follows:
1. Very short period
The first period of the modern periodic table is called very short period. It contains two
elements.
2. Short periods
The 2nd and 3rd periods of the modern periodic table are called short periods. They contain
8 elements each.
3. Long periods
The 4th and 5th periods of the modern periodic table are called long periods. They contain
18 elements each.
4. Very long periods
The 6th and 7th periods of the modern periodic table are called very long periods. The 6th
period consists of 32 elements and the 7th period consists of 26 elements.
132 GREEN Science (Chemistry) Book-10
Classification of Elements in Modern Periodic Table
In Modern Periodic Table, elements are classified into different categories on the basis of
characteristics as follows:
Metals, non-metals and metalloids
On the basis of conductivity, all the known elements have been classified into three
categories. They are:
1. Metals 2. Non-metals 3. Metalloids
1. Metals
Reactive metals are placed in the left side Do You Know
of modern periodic table except hydrogen
(H). The elements of group 1 like lithium The metals like Fe, Co, Ni, Ag, Au, Hg, Zn,
(Li), sodium (Na), potassium (K), etc. are the etc. are called transition metals because
most reactive metals. These metals react with they lie in between highly reactive metals
water and produce alkalis. Therefore, these and non-metals.
metals are called alkali metals. All metals
of group 2 and group 13 (except Boron) are
also metals. The elements of group 2 are called alkaline earth-metals as they are found on
the surface of the earth in the form of oxide and react with water to produce alkalis. The
metals of group 2 are less reactive than these of group 1 and the elements of group 13 are
less reactive than those of group 2. The metals of group 7 to group 12 are less reactive.
These elements are called transition metals.
2. Non - metals
Non-metals are placed in the right side of
the Modern periodic table. The elements of Do You Know
group 17, viz. Fluorine (F), Chlorine (Cl),
Bromine (Br), etc. are called halogens. These The elements of group 17, viz. F, Cl, Br, I
elements are the most reactive non-metals. and At are called halogens because they
These elements require only one electron to react with metals and form salts (halo-salt,
obtain octet state. So, these non-metals are genesis-producer.
highly reactive. The elements of group 15
like nitrogen (N), phosphorus (P), etc. and group 16 like oxygen (O) and sulphur (S) are
also non-metals. These non- metals are less reactive. Similarly, the non-metals of group
18, viz. He, Ne, Ar, Kr, Xe and Rn are called inert gases. These elements do not take part
in chemical reaction due to their duplet or octet state.
3. Metalloids
Metalloids are placed in between metals and non-metals in modern periodic table.
These elements show the properties of both metals and non-metals. Metalloids are poor
conductors of electricity. Their conductivity is more than that of non-metals and less
than that of metals. Silicon (Si), Germanium (Ge) and Bismuth (Bi) are some examples of
metalloids.
GREEN Science (Chemistry) Book-10 133
Activity 1
Study the modern periodic table shown in the textbook.
Copy the periodic table in a chart paper.
Identify metals, non-metals and metalloids in the periodic table.
Put a separate colour for metals, non-metals and metalloids.
Electronic Configuration of Elements on the Basis of Shells and Sub-
shells
In class 9, we studied electronic configuration of elements on the basis on shells. In class
10, we will study the electronic configuration of elements on the basis of shells as well as
sub-shells.
Atomic
number
Name and
symbol of
elements
Electronic
configuration
the basis of
shells
Electronic
configuration
on the basis
of sub - shells
Valency
1. Hydrogen (H) 1 × × × × × 1s1 1
0
2. Helium (He) 2 × × × × × 1s² 1
2
3. Lithium (Li) 2 1 × × × × 1s² 2s1 3
4
4. Beryllium (Be) 2 2 × × × × 1s² 2s² 3
2
5. Boron (B) 2 3 × × × × 1s² 2s² 2p1 1
0
6. Carbon (C) 2 4 × × × × 1s² 2s² 2p² 1
2
7. Nitrogen (N) 2 5 × × × × 1s² 2s² 2p³ 3
4
8. Oxygen (O) 2 6 × × × × 1s² 2s² 2p4 3, 5
2, 6
9. Fluorine (F) 2 7 × × × × 1s² 1s² 2p5 1
0
10. Neon (Ne) 2 8 × × × × 1s² 2s² 2p6 1
2
11. Sodium (Na) 2 8 1 × × × 1s² 2s² 2p6 3s1
12. Magnesium (Mg) 2 8 2 × × × 1s² 2s² 2p6 3s²
13. Aluminium (Al) 2 8 3 × × × 1s² 2s² 2p6 3s² 3p1
14. Silicon (Si) 2 8 4 × × × 1s² 2s² 2p6 3s² 3p²
15. Phosphorus (P) 2 8 5 × × × 1s² 2s² 2p6 3s² 3p³
16. Sulphur (S) 2 8 6 × × × 1s² 2s² 2p6 3s² 3p4
17. Chlorine (Cl) 2 8 7 × × × 1s² 2s² 2p6 3s² 3p5
18. Argon (Ar) 2 8 8 × × × 1s² 2s² 2p6 3s² 3p6
19. Potassium (K) 2 8 8 1 × × 1s² 2s² 2p6 3s² 3p6 4s1
20. Calcium (Ca) 2 8 8 2 × × 1s² 2s² 2p6 3s² 3p6 4s²
134 GREEN Science (Chemistry) Book-10
26. Iron (Fe) 2 8 14 2 × × 1s² 2s² 2p6 3s² 3p6 3d6 4s² 2, 3
29. Copper (Cu)
47. Silver (Ag) 2 8 18 1 × × 1s² 2s² 2p6 3s² 3p6 3d10 4s1 1, 2
79. Gold (Au) 2 8 18 18 1 × 1s² 2s² 2p6 3s² 3p6 3d10 4s² 1
4p6 4d10 5s1
2 8 18 32 18 1 1s² 2s² 2p6 3s² 3p6 3d10 4s² 1, 3
4p6 4d10 4f14 5s2 5p6 5d10 6s1
Sub-Shells or Orbitals
The main shells of atoms are K, L, M, N, O, P and Q. Each main shell consists of one or
more sub-shells or orbitals which are given below:
Main shells Sub-shells or orbitals
K(n = 1) s
L (n = 2) s, p
M (n = 3) s, p, d
N (n = 4) s, p, d and f
Each sub-shell can accommodate a certain number of electrons in it. The maximum
number of electrons that can be accommodated by sub-shells or orbitals is given below:
Sub-shells/orbitals Maximum number of electrons that can be accommodated in
the sub-shell
s2
p6
d 10
f 14
On the basis of preferential filling of the last electron, elements are classified into four
blocks. They are as follows:
1. s – Block elements 2. p – Block elements
3. d – Block elements 4. f – Block elements
1. s – Block elements
The elements of group 1 and 2 are called s - Block elements because their last electron
enters into s - orbital or sub-shell. The elements whose last electron enters into s-sub-shell
are called s - Block elements. These elements are placed at the extreme left side of the
modern periodic table.
The last electron of potassium (K) enters into 4s sub - shell. So, potassium is called s –
Block element. Similarly, the last electron of magnesium (Mg) enters into s sub-shell. So,
it is also called s - Block element.
s - Block elements form electropositive ions by losing 1 or 2 electrons from their outermost
shell. All elements of s - Block are metals except hydrogen (H) and Helium (He).
GREEN Science (Chemistry) Book-10 135
2. p - Block elements
The elements of groups 13, 14, 15, 16, 17 and 18 or 0 (zero) are called p - Block elements as
their last electron enters into p - sub - shell. Those elements whose last electron enters into
p - sub - shell are called p - Block elements. p - Block elements are placed at the right side
of the modern periodic table. These elements may be metals, metalloids or non-metals.
The sub - shell electronic configuration of Aluminum (Al) is 1s² 2s2 2p6 3s2 3p1. Its last
electron enters into p - sub - shell of 3p orbital. So, it is called p - Block element. Similarly,
Argon (Ar) is also called p - Block element because its last electron enters into p - orbital
– (Ar - 1s² 2s² 2p6 3s² 3p6)
3. d - Block elements
The elements of groups 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 are called d - Block elements because
their last electron enters into d - orbital of the penultimate shell. d - Block elements are
kept in between s - Block elements and p - Block elements. The elements of d - Block are
called transition metals as they are placed between active metals and non-metals. Iron
(Fe) and Copper (Cu) are called d-Block elements because their last electron enters into
d-orbital of the penultimate shell.
Fe – 1s², 2s² 2p6, 3s² 3p6, 4s², 3d6
Cu – 1s², 2s² 2p6, 3s² 3p6, 4s² 3d10
4. f - Block elements
The elements of Lanthanide series and Actinide series are called f - Block elements. The
elements whose last electron enters into f - orbital of ante-penutimate shell are called f -
Block elements. These elements are kept at the bottom of modern periodic table just below
d - Block elements. The elements of f - Block are also called inner - transition metals. The
properties of f - Block elements are similar to that of d-Block elements. However, their last
electrons enter f - orbital of ante - penultimate shell. So they are kept just below d - Block
elements in the modern periodic table.
Activity 2
Study the modern periodic table given in your textbook.
Observe the position of s – Block, p – Block, d – Block and f – Block elements.
Prepare a list of s – Block, p – Block, d – Block and f – Block elements in a chart
paper.
136 GREEN Science (Chemistry) Book-10
Aufbau Principle
Aufbau principle states that, "The elements in an atom are so distributed that they occupy
orbits in order of their increasing energy". Form this principle it becomes clear that the
orbits having low energy level are filled faster than the orbits having high energy level as
shown in the given order.
1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s < 5f < 6d < 7p
Do You Know
Aufbau principle was propounded
by Wolfgang Pauli and Neils
Bohr. According to this principle,
electrons always try to enter into the
shell having low energy level.
Fig.
7.3
Characteristics of Groups and Periods in Modern Periodic Table
1. Valency
Valency can be defined as the number of electrons lost, gained or shared by atoms during
a chemical reaction. It can also be defined as the combining capacity of an atom with
another to form a molecule.
The valency of all elements in a group Do You Know
remains the same because they have the
equal number of electrons in their valence Valence electrons are the electrons present in
shell. the outermost shell. In a group the number
of valence electrons remains the same but
In a period, the valency of elements increases by one in a period while moving
increases gradually from 1 to 4 while from left to right.
moving from left to right and then
decreases form 4 to zero (0).
2. Atomic size
Atomic size of an atom is defined as the distance between the outermost shell and the
centre of the nucleus of that atom. Atomic size is also called atomic radius.
GREEN Science (Chemistry) Book-10 137
Variation of atomic size in a group
The atomic size of atoms increases while moving from top to bottom in a group.
Group 1 Atomic size Group 17 Atomic size
Li Li F F
Na Cl Cl
Na
K Br
K Br
Rb I I
Rb
Cs At At
Cs
Fr
Fr
From the above table, it becomes clear that the smallest atom lies at the top and the largest
atom lies at the bottom of a group. When we move from top to bottom of a group, a new
shell is added in every step. So atomic size increases gradually from top to bottom in a
group.
Variation of atomic size in a period
When we move from the left to right in a period, the atomic number increases by one in
each step. Due to this, the number of protons and neutrons increases in the nucleus but
extra electron is added to the same shell. Due to this, the outermost shell is pulled inwards
due to increasing nuclear charge. As a result, the atomic size decreases gradually while
moving from the left to right in a period.
Elements of 2nd period Li Be B C N O F
Elements of 3rd period Na Mg Al Si P S Cl
138 GREEN Science (Chemistry) Book-10
3. Nuclear Charge or Nuclear Power
Nuclear charge or nuclear power is the total amount of energy required to remove the
outermost electron of an atom.
The nuclear power decreases gradually in a group while moving from top to bottom and
increases in a period while moving from the left to right.
4. Electronegativity
Electronegativity can be defined as the amount of energy required for an atom to attract
outer electron of an atom during chemical reaction.
Electronegativity decreases gradually from top to bottom in a group and increases
gradually from left to right in a period.
5. Metallic character and Non-metallic character
The tendency of an atom to lose electron/s from its valence shell is called metallic character
of that atom.
The metallic character increases gradually from top to bottom in a group and decreases
gradually from left to right in a period.
The tendency of an atom to gain or attract electron/s from valence shell of other atom is
called non-metallic character.
The non-metallic character decreases gradually from top to bottom in a group and
increases gradually from the left to right in a period.
Chemical Reactivity of Elements
In modern periodic table, metals are placed in the left side. Metals have tendency to lose
electron/s from their valence shell. The metals which can lose electrons easily from their
valence shell are called active metals. The metals of group 1 are highly reactive in nature.
Non-metals are placed in the right side of the modern periodic table. The non-metals
which can gain electron/s easily are called active non-metals. The chemical reactivity of
metals and non-metals depends on various factors such as atomic size, nuclear power,
metallic character, non-metallic character, number of valence electrons and so on.
Reactivity of Elements in a Period
Metals are placed in the left side of period in the modern periodic table and non-metals
are placed in the right side of period in the modern periodic table. The atomic size of
elements decreases gradually while moving from the left to right in a period. Therefore,
chemical reactivity of metals decreases gradually while moving towards right side.
Similarly, the chemical reactivity of non-metals increases gradually upto group 17. While
moving towards right side of a period.
GREEN Science (Chemistry) Book-10 139
Elements of 2nd period Li Be B C NO F
Chemical reactivity Most Least Most reactive
reactive reactive non-metal
metal
Chemical reactivity decreases Chemical reactivity
increases
Elements of 3rd period Na Mg Al Si P S Cl
Chemical reactivity Most Least Most reactive
reactive reactive non-metal
metal
Reactivity decreases Reactivity increases
Reactivity of Metals in a Group
Metals have tendency to lose one, two or three electrons from their valence shell during
chemical reaction. The chemical reactivity of metals increases gradually while moving
from top to bottom in a group.
Group 1
Li Least reactive metal
(Smallest atom)
Na
K
Chemical reactivity
of metals increases
Rb while moving from
top bottom in a
group
Cs
Fr Most reactive metal
140 GREEN Science (Chemistry) Book-10 (Largest atom)
The atomic size of metals increases while moving from top to bottom in a group. Due to
this, the tendency of metallic atom to lose electrons increases as the valence shell remains
far away from the nucleus. As a result, chemical reactivity of metals increases while
moving from top to bottom in a group.
Reactivity of Non-metals in a Group
Non-metals have tendency to gain electron/s during chemical reaction. The chemical
reactivity of non-metals decreases gradually while moving from top to bottom of a group
due to increase in atomic size. When the atomic size of non-metals increases, the tendency
of these atoms to gain electrons decreases.
Group 17
F Most reactive non-metal
(Smallest atom)
Cl
Chemical reactivity
of non-metals
Br decreases while
moving from top to
bottom in a group
I
At Least reactive non-metal
(Largest atom)
Solved Question: 1
Why is potassium more reactive than sodium though both lie in the same group?
Ans:
Both potassium and sodium lie in the same group as both have one electron in their
valence shell. Both of them have the same valency and both elements lose one electron
from their valence sell. But the atomic size of potassium is larger than that of sodium.
Due to this, the tendency of potassium to lose electron increases due to larger atomic size.
Therefore, potassium is more reactive than sodium though both lie in the same group.
Solved Question: 2
Why is fluorine more reactive than chlorine though both lie in the same group?
Ans:
Both fluorine and chlorine are the non-metals of the same group and both of them gain
one electron from other reactive metals. But atomic size of fluorine is smaller than that
GREEN Science (Chemistry) Book-10 141
of chlorine. Due to this, electronegativity of fluorine is more than that of chlorine. So,
nuclear power of fluorine atom increases to gain electrons. Therefore, fluorine is more
reactive than chlorine though both lie in the same group.
Key Concepts
1. Classification of elements is the grouping of elements on the basis of their similarities
and differences.
2. The table in which elements are kept different groups on the basis of characteristics
is called periodic table.
3. Mendeleev's periodic law states that, "The physical and chemical properties of
elements are a periodic function of their atomic weights."
3. Mendeleev's classification of elements was the first scientific study of the elements.
He classified elements into groups and periods in the form of a table which is
known as Mendeleev's periodic table.
4. The position of hydrogen in Mendeleev's periodic table is not clear because it can
be placed in group 1 along with alkali metals and in group 17 along with halogens.
5. Modern periodic rule states that, "The physical and chemical properties of elements
are a periodic functions of their atomic numbers".
6. The 14 elements from atomic number 58 to 71 after Lanthanum (La) are called
Lanthanides. Similarly, the 14 elements from atomic number 90 to 103 after
Actinium (Ac) are called Actinides.
7. Isotopes are the elements having the same atomic number but having different
atomic mass.
8. The metals like Fe, Co, Ni, Ag, Au, Hg, Zn, etc. are called transition metals because
they lie in between highly reactive metals and non-metals.
9. The elements of group 2 are called alkaline earth-metals as they are found on the
surface of the earth in the form of oxide and react with water to produce alkalis.
10. Non-metals are placed in the right side of the Modern periodic table. The elements
of group 17, viz. Fluorine (F), Chlorine (Cl), Bromine (Br), etc. are the most reactive
non-metals.
11. Metalloids are placed in between metals and non-metals in modern periodic table.
These elements show the properties of both metals and non-metals.
12. The elements whose last electron enters into s-sub-shell are called s - Block elements.
These elements are placed at the extreme left side of the modern periodic table.
13. Those elements whose last electron enters into p - sub - shell are called p - Block
elements. p - Block elements are placed at the right side of the modern periodic
table.
14. The elements of groups 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 are called d - Block elements
because their last electron enters into d - orbital of the penultimate shell.
15. The elements of Lanthanide series and Actinide series are called f - Block elements.
The elements whose last electron enters into f - orbital of ante-penutimate shell are
called f - Block elements.
142 GREEN Science (Chemistry) Book-10
16. Aufbau principle states that, "The elements in an atom are so distributed that they
occupy orbits in order of their increasing energy".
17. Atomic size of an atom is defined as the distance between the outermost shell and
the centre of the nucleus of that atom. Atomic size is also called atomic radius.
18. When we move from top to bottom of a group, a new shell is added in every step.
So atomic size increases gradually from top to bottom in a group.
19. The atomic size decreases gradually while moving from the left to right in a period.
20. Nuclear charge or nuclear power is the total amount of energy required to remove
the outermost electron of an atom.
21. Electronegativity can be defined as the amount of energy required for an atom to
attract outer electron of an atom during chemical reaction.
22. The tendency of an atom to lose electron/s from its valence shell is called metallic
character of that atom.
23. The tendency of an atom to gain or attract electron/s from valence shell of other
atom is called non-metallic character.
24. The chemical reactivity of metals increases gradually while moving from top to
bottom in a group.
25. The atomic size of metals increases while moving from top to bottom in a group.
Due to this, the tendency of metallic atom to lose electrons increases as the valence
shell remains far away from the nucleus. As a result, chemical reactivity of metals
increases while moving from top to bottom in a group.
26. The chemical reactivity of non-metals decreases gradually while moving from top
to bottom of a group due to increase in atomic size. When the atomic size of non-
metals increases. The tendency of these atoms to gain electrons decreases.
Sequential General Exercise 1
1. Choose the best answer from the given alternatives.
a. Which of the given elements is an alkaline earth-metal?
sodium magnesium aluminium calcium
4
b. What is the valency of aluminium? Ni
1 2 3
c. Which of the following is an inert gas?
Ne Na N
GREEN Science (Chemistry) Book-10 143
d. Which of the following is the most reactive metal?
Li Na K Cs
e. Which of the following is the most reactive non-metal?
F Cl Br I
2. Answer the following questions.
a. What is periodic table?
b. What is meant by classification of elements?
c. Why are elements classified?
d. State Mendeleev's periodic rule.
f. Write any two characteristics of Mendeleev's periodic table.
g. What are groups and periods?
h. Write any three defects in Mendeleev's periodic table.
i. On what basis did Moseley develop periodic table?
j. State modern periodic law.
k. Write down the number of groups and periods in modern periodic table.
l. Write any four characteristics of modern periodic table.
m. Write down the position of metals, non-metals and metalloids in modern periodic
table.
n. Write down the position of alkali metals, alkaline earth-metals, halogens and
inert gases in modern periodic table.
o. Write down the electronic configuration of Na, Si, Cl , K, Ca Fe and Cu on the
basis of sub-shells.
3. Write down electronic configuration of given elements on the basis of sub shells.
a. Oxygen b. Neon
c. Aluminium d. Phosphorus
e. Chlorine f. Potassium
4. What are s-Block elements? Give any two examples.
5. What are p - Block and d - Block elements. Where are they located in modern
periodic table?
6. What are f-Block elements? Give any two examples.
7. What are Lanthanides and Actinides? Where are they placed in the periodic table?
8. How does chemical reactivity of elements vary while moving from left to right in
a period? Describe.
144 GREEN Science (Chemistry) Book-10
9. How does chemical reactivity of metals vary while moving
a. down in a group ?
b. from left to right in a period?
10. Study the given table and answer the following questions.
A 1s² 2s² 2p6 3s1
B 1s² 2s² 2p6 3s²
C 1s² 2s² 2p6 3s² 2p5
a. Name the element A, B and C. Also, write their block, period, group and valency.
b. Which element is more reactive out of A and B, why?
c. Identify non-metal and metals.
11. Differentiate between
a. Periods and groups
b. Mendeleev's periodic table and modern periodic table
c. s - Block and p - Block elements
d. Alkali metals and halogens
e. Halogens and inert gases
12. Give reason.
a. Chemical reactivity of metals increases while moving down in a group.
b. Chemical reactivity of metals decreases while moving from left to right in a period.
c. Chemical reactivity of non-metals decreases while moving down in a group.
d. Sodium is more reactive than magnesium.
e. The elements of group 1 are more reactive than the elements of group 2.
f. Chlorine is less reactive than fluorine.
g. The position of hydrogen is still controversial in the modern periodic table.
13. Which element is more reactive out of:
a. oxygen and sulphur?
b. lithium and sodium?
c. potassium and calcium?
d. sulphur and chlorine?
14. Identify the block of the given elements.
K, Ca, Na, N, S, Al, Si, P
Cu, Zn, Fe, Mn, Au, Hg, Ag
15. Differentiate between metals and non-metals. Write down their position in modern
periodic table.
GREEN Science (Chemistry) Book-10 145
Grid-based Exercise 2
Group ‘A’ (Knowledge Type Questions) (1 Mark Each)
1. On which basis did Mendeleev form the periodic table?
2. State Mendeleev’s periodic rule.
3. State the Modern periodic law.
4. Define s-Block elements.
5. What is electronic configuration?
6. How many periods are there in the Modern periodic table?
7. Mention the position of metals and non-metals in the Modern periodic table.
8. Mention the position of alkaline earth-metals in the Modern periodic table. What is
their valency?
9. What are halogens? Give one example. F
Cl
10. Write down the common name of the elements shown in the given Br
table. I
11. In which groups of the Modern Periodic Table are there alkali metals and inert
gases?
12. What are transition metals?
13. Define Actinides.
14. In what groups do magnesium and nitrogen belong in Modern periodic table ?
15. Write the name of the groups in which very active metals and very active non-metals
are placed in modern periodic table.
Group ’B’ (Understanding Type Questions) (2 Marks Each)
16. Distinguish between Modern periodic table and Mendeleev’s periodic table in two
points.
17. What is the valency of halogens? Why?
18. Argon atom can exist freely in nature, why?
19. What is the cause for placing Calcium in 2 or IIA group of the Modern periodic table?
20. Among magnesium and calcium, which element is more active ? Give reason. 1
H
21. Why is fluorine more active than chlorine although both lie in the same group? Li
Na
22. A small portion of modern periodic table (Group 1) is given. Give two reasons K
of placing hydrogen along with metals in this group. Rb
23. Elements of group 1,2,13 are more reactive as they go down in the group of
the periodic table, why?
146 GREEN Science (Chemistry) Book-10
24. Atomic size of elements decreases on moving from left to right in a period.
25. Atomic size of elements increases on moving from top to bottom in a group.
26. Modern periodic table is less defective than Mendeleev’s periodic table. Give two
reasons.
27. Elements of group 15,16 and 17 are less reactive as they go down in the group of the
modem periodic table, why?
Group ‘C’ (Application Type Questions) (3 Marks Each)
28. Mention any three drawbacks of Mendeleev’s periodic table.
29. Which group of the periodic table (Element) (Electronic configuration)
does the element ‘A‘ belong to? Which A 2,8,5
element is more reactive in between ‘B’ B 2,3
and ‘C’? Write with reason. C 2, 8,3
30. Write any three characteristics of
Modem periodic table.
31. Observe the given table and answer the following questions:
Element Electronic configuration
A 2,7
B 2,8,1
C
D 2,8,8,1
2,8, 7
i. What is the valency of ‘B’ and why ?
ii. Which element is more active in between A and D, why ?
32. Electronic configuration of two elements is given below. Study the configuration and
answer the following questions:
A → 1s2, 2s2, 2p4 B → 1s2, 2s2 ,2p6, 3s1
i. Which block of periodic table does element ‘B’ belong to and what is its valency ?
ii. Give the names of element ‘A’ and ‘B’ and also write down the molecular formula
of the compound formed by the combination of these two elements.
Group ’D’ (Higher Abilities Type Questions) (4 Marks Each)
33. Which block of the periodic table does the element ‘B’ belong to? Why? Which element
is the most reactive among ‘A’, ‘C’ and ‘D’? Write with reason.
Element Electronic configuration
A 1s2,2s2,2p6,3s2
B 1s2,2s2,2p1
GREEN Science (Chemistry) Book-10 147
C 1s2,2s2,2p6, 3s2,3p6,4s2
D 1s2,2s2
34. A part of periodic table is given below. Study it and answer the following questions:
1+2+1
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
i. How are these elements arranged?
ii. Which one is more active out of Be and Mg. Why?
iii. Write down the formula of a compound made from Na and O.
35. Write any two characteristics of Modern periodic table. Study the table given below
and answer the following questions: 1+1+2
Elements Electronic configuration
P 1s2 2s2 2p6 3s1
Q
R 1s2 2s2 2p6 3s2 3p6 4s1
1s2 2s2 2p6
i. What is the valency of element R ?
ii. Which is more active between the elements P and Q, why ?
36. Give the answer of the following questions with the help of the given table:
Na Mg Al Si P S Cl Ar
2.8.1 2.8.2 2.8.3 2.8.4 2.8.5 2.8.6 2.8.7 2.8.8
i. Which period do the given elements belongs to? Why ?
ii. Which blocks do Mg and Ar belong to? 2+2
iii. Identify one active metal and inert gas.
37. Answer the following questions on the basis of the table :
1s 2s 2p 3s 3p 3d 4s 4p 4d 4f
A2 2 6 1
B2 2 6 2 5
C2 2 6 2 6 10 1
D2 2 6 2 1
i. Which blocks of periodic table do the element ‘A’ and ‘B’ belong to ? Why?
ii. What are the valencies of elements ‘B’ and ‘D’? Why?
148 GREEN Science (Chemistry) Book-10
UNIT Chemical Reaction
8
Weighting Distribution Theory : 5 Practical: 2
Before You Begin
When we burn a piece of paper, it changes into ash and gas. When we
burn firewood, kerosene, coal, etc., we can see the formation of smoke.
In these cases, one from of a matter changes into another matter having
different chemical properties. Such types of change in matter is called
chemical change. It occurs as a result of chemical reaction. The process
of chemical change is expressed in chemical reaction. The combination,
decomposition or replacement that occurs in the molecules of matter
during a chemical change is called chemical reaction. We have studied
general introduction to chemical reaction in class 9. In this unit, we will
study the types of chemical reaction, chemical equations, the factors
affecting the rate of chemical reaction and catalyst with its types in brief.
Learning Objectives Syllabus
After completing the study of this unit, students will be able to: • Introduction to chemical
i. classify different types of chemical reaction with reaction
examples. • Types of chemical reaction
– Combination reaction
ii. write chemical change in the form of chemical – Decomposition reaction
equation. – Displacement reaction
iii. explain the factors that affect the rate of chemical – Acid-base reaction
reaction.
• Factors affecting chemical
iv. introduce catalyst with its types and examples. reaction
– Temperature
– Pressure
– Surface area
– Light
• Catalyst and its types
Glossary: A dictionary of scientific/technical terms
decomposition : dissociation, breaking down
displacement : replacement
neutralization : an act or process of neutralizing, to cause a chemical to be neither an acid,
nor a base
catalyst : the chemical substance which can increase or decrease the rate of a
chemical reaction being itself chemically unchanged
exothermic : the chemical reaction that evolves heat
endothermic : the chemical reaction that requires heat for the chemical change
GREEN Science (Chemistry) Book-10 149
Chemical Reaction
The chemical bond present in the molecules Do You Know
of reactants breaks due to heat, light,
electricity, etc. during a chemical change. Losing, gaining or sharing of electrons
Then combination, dissociation or exchange by an atom to gain stable electronic
take place between the atoms and molecules configuration is the major cause of
of reactants to form new substances called chemical reaction.
products. This process is called chemical
reaction.
The combination, decomposition, displacement or neutralization that occurs in molecules
of matter during a chemical change is called a chemical reaction.
When carbon burns in air or oxygen, it forms Carbon dioxide.
Carbon + Oxygen burn Carbon dioxide
C + O2 CO2 [Combination]
When calcium carbonate is heated, it decomposes into calcium oxide and carbon dioxide.
Calcium carbonate heat Calcium oxide + Carbon dioxide
CaCO3 CaO + CO2 [Decomposition]
When magnesium reacts with suphuric acid, it forms magnesium sulphate and hydrogen
gas.
Magnesium + Sulphuric acid Magnesium sulphate + Hydrogen
Mg + H2SO4 MgSO4 + H2 [Displacement]
When hydrochloric acid reacts with sodium hydroxide, it forms two neutral substances,
viz. salt and water. This process is called neutralization reaction.
Hydrochloric acid + Sodium hydroxide Sodium chloride + Water
HCl + NaOH NaCl + H2O
The above examples show that a chemical change is expressed in both word equation and
formula/chemical equation.
Word Equation
A word equation is the chemical reaction expressed by writing the full names of reactants
and products. A word equation is less informative than the chemical equation. Some
examples of word equation are given below:
Sodium + Chlorine Sodium chloride
Hydrogen + Oxygen Water
150 GREEN Science (Chemistry) Book-10
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