Blooming Science-10-2077- final press

plates of soft iron are placed one above the other insulating from each other. Two electrically
insulated coils insulated from each other are wound on the metallic frame. The coil to which
the energy is supplied is called the primary coil and the coil from which the energy is delivered
to the outer circuit is called the secondary coil.

The rectangular metallic frame in which the coils are wound is called the core of the transformer.
The core is laminated and insulated with varnish or shellac. This reduces the eddy current loss.

Theory of Working: In a transformer, alternating current is passed through the primary coil (P).
We know the magnitude and direction of alternating current changes all times as in figure. above.
This varying current in the primary coil changes the magnetic field through the core of iron and
which causes change in magnetic lines of force in the secondary coil. The change of magnetic
lines of force through the secondary coil creates induced e.m.f. in the secondary coil.

The magnitude of e.m.f. induced is proportional to the rate of change of lines of force. The
amplitude of the induced e.m.f. is proportional to the ratio of the number of turns in the secondary
to the primary coils.

Thus, for a transformer,

Primary voltage Number of turns in Primary coil
Secondary voltage = Number of turns in Secondary coil

In the symbols, VP = VP Scan for practical experiment
VS NS

There are two types of transformers:

(i) Step up transformer

(ii) Step down transformer

The transformer which changes the low voltage alternating current visit: csp.codes/c10e08
to high voltage alternating current is called step up transformer. The

transformer which changes high voltage alternating current to low voltage alternating current is

called step down transformer.

In a step up transformer, the number of turns in the secondary coil is more than the number of
turns in the primary coil. i.e., Ns.>Np and Vs > Vp

While in a step down transformer, the number of turns in the secondary coils is less than the
number of turns in the primary coil. i.e., Ns.< Np and Vs < Vp

Uses: We use transformer in electrical devices which operate at a voltage other than the voltage

supplied from the main supply. In our country we use alternating voltage of 220V.

Step up transformers are used in CRT televisions. They transform the 220 V mains voltage into
almost 20000 V. It is used in hydropower station to uplift the a.c. voltage upto 2,32,000V for a long
distance transmission of a.c. current.

Step down transformer are used in electric bells and in radio sets. They transform the main voltage
into much smaller and safer voltage, which is less likely to damage you and your equipment. It is
also used in power sub-station to reduce voltage before supplying to our home.

Blooming Science Book 10 101

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Solved Numericals

Example 1: A transformer lowers down 220V from main supply to 12V to operate an electric
iron. If the primary coil has 880 turns, how many turns should there be on the
secondary coil?

Solution: Here, = 12V
Secondary voltage = 220 V
Example 2: Primary e.m.f. voltage = 880
Solution: Number of turns in primary coil =?
Number of turns in secondary coil

Let the number of turns be x

We have, for a transformer,

Secondary voltage Number of turns in secondary coil
Primary voltage. = Number of turns in primary coil
x
or, 12 = 880
220
880
or, x = 220 × 12 = 4 × 12 = 48.

Therefore, the number of turns in the secondary coil is 48.

A transformer steps up 220V from the main supply to the 1980V. (i) What is the
turns ratio of the transformer windings? (ii) How many turns are on the primary
if the secondary has 900 turns?

Here, = 220V
Primary Voltage (Vp) = 1980V
Secondary Voltage (Vs) = (Ns)
Let, Number of secondary turns = (Np)
Number of primary turns

102 Blooming Science Book 10

(a) We have, for a transformer,

or, Ns Vs
Np = Vp

Ns 1980 Np 220 1
Np = 220 or, Ns = 1980 = 9

Therefore, turns ratio = 1

9

(b) Number of turns in secondary coil (Ns) = 900

Numbers of turns in primary coil (Np) = ?

We have,

Ns Vs
Np = Vp

Ns 1980 900 1980
or, Np = 220 or, Np = 220

220 900

or, Np = 1980 × 900 = 90 = 100

Therefore, the number of turns in primary coil = 100

Example 3: A transformer operates from 240V a.c. supply to give an output of 8V for
ringing a door bell. If the primary coil has 3000 turns, calculate the number of
turns in the secondary coil.

Solution: Here,

Primary voltage (Vp) = 2400V

Secondary voltage (Vs) = 8V

Number of turns in primary coil (Np) = 3000

Number of turns in secondary coil (Ns) = ?

We have, for a transformer

Ns Vs or, Ns = 8 × 3000 = 100
Np = V 240

p

Therefore, the number of turns in the secondary coil = 100.

Some electrical appliances and their uses

1. Battery charger

The electrical device which is used to charge rechargable battery is called a battery cnarge.
It converts AC voltage into DC voltage and store in the battery. Mobile charger is an example
of it. In some devices the charger is connected with inbuilt battery. One of the end of charger is
connected to the battery and another end is connected to the supply of current. As electric current
is passed into the device, the battery gets charged.

Blooming Science Book 10 103

2. Adaptor

The device which supplies power to the electronic device that needs less voltage is called
‘Adaptor’.

It is the linear power supply circuit formed by the combination of transformer, rectifier and filter
circuit. The transformer helps to decrease the quantity of input AC to the adaptor which rectifier
converts AC into pulsating DC (Fluctuating DC) and filter at the same time helps to change
pulsating DC into smooth wave form. There are different types of adapter but in most of the
electric appliances AC to DC power adapter or AC/DC power supply is used.

This type of adaptor takes AC from wall outlet and gives regulated or maintained or constant DC
voltage. For e.g. adapter of laptop, cell phone etc.

Advantages of using adapters in electronic devices

1) The uses of adapter reduce the shape, size and weight of the electronic appliances so that
it can be portable.

2) It reduces heat produced into the gadget.

3) It can provide constant voltage to the device so that electronic device is protected from
any damages.

4) It can be easily replaced, if it is damaged.

3. Inverter

The term inverter was first coined by David Chandler Prince in 1925 AD when means simply the
conversion of DC into AC.

An electrical device which is used to convert AC into DC and then DC voltage into AC voltage
is called an inverter. A block diagram of inverter is shown in the picture.

Controller Driver Output Output Socket
Circuit Circuit Circuit

AC Battery Battery
Charger
input

The design of inverter is too complicated. It converts 12 V DC to 12V AC which is then converted

into high AC with the help of step up transformer. During loadsheading, the DC current stored in

battery is converted in AC by it. When there is electricity, it converts AC current into DC to

charge the battery. In this was the inverter works. +1

The output of the inverter is always AC which has the

fluctuating or has frequency. The variation is from -1 to +1

and can be shown by trigonometric sine curve.

There are different types of inverter but most acceptable is –1

sine wave (sine curve) inverter.

104 Blooming Science Book 10

4. Solar Cells

The solar cells are the devices which convert the solar
energy directly into electrical energy. A simple construction
of a solar cell and its application is illustrated in figure . It
consists of a series of semiconductor device called diode.
When solar energy falls on such a diode, a small potential
difference is created across it. If a series of diodes are
connected, a large potential difference can be obtained. If a
large number of series of diodes are connected in parallel,
a large current can be obtained. Each diode is called a solar
cell and any series of such cells is called a solar battery (or
a solar cell panel).

Electrical Power consumption

Electrical energy consumed by any devices is calculated by,

Electricity consumption = Electricity power × time

Electricity consumption = P(w) × T (hr)

One kilowatt hour is the electrical energy consumed by the electric appliance of power 1 KW
when it is used for 1 hour.

1 KWh = 1 kilowatt × 1 hour

= 1000 watts x (60 x 60) seconds

= 3600000 Joules = 1unit.

∴ 1 KWh = 3.6 x 106 Joules

The electric meters of our houses measure consumed electricity in KWh. One kilowatt hour means
1 unit of electricity. The electricity consumed by N appliances of same power can be written as:

Electrical Energy (E) = Power (in Kw) × number (N) × time (in hours)

or, E = P(in Kw) × t (in hours) × N

Cost of Electricity (Electric Bill)

The consumption of electric energy in the various domestic appliances such as lamps, bulbs,
cookers, irons, fans, heaters, televisions, etc are concerned mainly with the power of the
appliances and the time for which they are used. Thus, the consumption of electricity is given by

Consumption of = Electric power × time = kilowatt hour
electricity (in kilowatt) (hours) (kwh)

The electricity Board of our country “Nepal Electricity Authority (NEA)” charges the cost of
consumed electricity in the unit of kilowatt hour. At present, a ‘unit’ costs about 7 rupees and 30
paisa (minimum reading cost).

Knowing the cost of 1 unit of electricity, we can find out the total cost of electricity.

Cost of electricity = Consumed unit × Price of one unit

Blooming Science Book 10 105

Safety measures in using electricity

i) Electrical wire must be properly insulated.

ii) Suitable fuses must be connected in every rooms or in every floors of house

iii) Fuses and switches must be in the live side of the wire.

iv) Earthing must be done to heavy electrical devices.

v) Colour codes of the wires must be used during house wiring. Red/Brown colour wire is
for live side, Black/blue/white wire for neutral side and yellow/green colour wire is used
for earthing.

Solved Numericals

1. A factory uses 300 lamps. The lamps consume 60 watt each and lighted for 10 hours daily.
Find the cost of electricity for a month if the electricity costs Rs. 6 per unit.

Solution: Here,
Power of each lamp = 60W
Since there are 300 lamps,
the power of 300 lamps = 60 × 300 = 18000W = 1.8kw
∴ Electrical energy consumed in 10 hours
= Power x time = 1.8 × 10 = 18 kwh = 18 units
So for one month,
Total energy consumed = 18 × 30 = 540 units
∴ 1 unit cost = Rs. 6
∴ 540 unit cost = Rs. 6 × 540 = Rs. 3240

2. One student is using an electric bulb of 100 watt for 6 hours daily. Find the consumption
of electric energy in a month of 30 days. If the electricity costs Rs. 3 per unit, what will be
the cost of electricity supplied?

Solution: Here,

Power of the bulb = 100 w = 0.1 kw

Time = 6 hours

∴ Energy consumed = 0.1 × 6 = 0.6 kwh = 0.6 unit

So, for one month, total energy consumed

= 0.6 × 30 = 18 units

Since, 1 unit costs = Rs. 3.00

∴ 18 unit costs = Rs. 3 × 18 = Rs. 54

106 Blooming Science Book 10

3: In a house, 5 bulbs of 60W glow for 4 hours everyday. An electric press of 750W is used to
press cloth for an hour a day, and the five electric fans of 150W is used for 8 hours a day.

Find the cost of electricity for 15 days, if the cost of electricity per unit is 3
rupees.

Solution:
(i) Electric power of 5 bulbs = 5 × 60 = 300W = 0.3 kw
Time = 4 hours
∴ Energy consumed = 0.3 × 4 kwh = 1.2 unit
(ii) Electric power of a press = 750W = 0.75 kw
Time = 1 hours
∴ Energy consumed = 0.75 × 1 kwh = 0.75 unit
(iii) Electric power of five fans = 5 × 150 = 750W = 0.75 kw
Time = 8 hours
∴ Power consumed = 0.75 × 8 kwh = 6.0 kwh = 6 unit
∴ Total Energy = 1.20 + 0.75 + 6 = 7.95 unit
∴ For 15 days = 7.95 x 15 = 119.25 units
Since, 1 unit costs = Rs. 3

∴ 119.25 unit costs = Rs. 3 × 119.25 = Rs. 357.75

Let's Learn

1. Inert gases like Argon or Nitrogen are filled inside the electric bulb because it prevents the
evaporation of the filament at high temperature.

2. Mercury vapour is used in fluorescent lamp. It is because it produces ultraviolet radiations
when the electrons collide with mercury atoms.

3. A live wire is not allowed to come in contact with the neutral or the earth wire. This is
because the circuit is completed and hence a large current flows through the wires. A lot
of heating occurs in the wire due to the over flow of current and this may lead to fire.

4. Soft magnetic materials are used for making electromagnets. This is because such materials
magnetize and demagnetize easily, which is necessary for a temporary magnet.

5. 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.

6. If a direct current is applied to the primary coil of a transformer, it does not produce
varying magnetic field in its secondary coil. Thus, there is no change in 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.

7. Iron core of a transformer is laminated the core of transformer is combination of a number

Blooming Science Book 10 107

of rectangular strips of soft iron. These strips are insulated to each other by shellac or
varnish. This is called lamination of iron core. The 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. Fuses and switches are connected in live side of wire. When fuses and switches are in off
condition, no current flows through live side of wire and prevent us from electric shocks
during maintenance.

9. Heavy electrical devices must be earthed because earthing wire carries the leakage current
from heavy electric devices to earth and protect us from electric shocks.

Points to Remember

1. Effect of Electric Current:

(i) Heating and lighting effect

(ii) Chemical effect

(iii) Magnetic effect

2. The wire used in heating devices is called a filament. Nichrome wire is an alloy of 60% of
nickel and 40% of chromium.

3. The filament lamp uses a filament of tungsten wire having the melting point 3400oC.

4. A magnetic field is set up around a wire when current is allowed to pass through it.
This magnetic field deflects the compass needle. It was first discovered by Oerested in
1820 AD.

5. Solenoid: The coil obtained by wounding a wire in the form of a cylinder wire is called a
solenoid.

6. Electromagnet: When a soft iron rod is placed inside a solenoid and current is passed
through the coil, the rod becomes temporary magnet. Such temporary magnet is called
Electromagnet.

7. Generator or Dynamo: A generator or dynamo converts mechanical energy to electrical
energy. Generators use the principle of electromagnetic induction.

8. Transformer: It is an electrical device which is used to increase or decrease the voltage of
alternating current.

Principle: It works on the principle of electromagnetic induction or principle of mutual
induction.

There are two types of transformers.

(i) step up transformer (ii) step down transformer

9 The electronic device which supplies energy by conducting current through the secondary
cell or battery is called charger.

10. Fuse is a circuit breaker made up of lead or tin with low melting point and high resistivity.

108 Blooming Science Book 10

11. Electricity consumption is the product of power in KW with time in hour. It unit is KWh.

12. The external power supply given to the electronic device that contains batteries or don’t
contain any power source is called ‘Adaptor’.

13. An electrical device which is used to convert DC voltage into AC voltage is called an
inverter.

Project Work
1. Take a dry cell of 1.5 V. Complete an electric
circuit with the help of some connecting wires
and a bulb. Observe the brightness of the bulb.

Then divide the dry cell into two equal parts
and connect them with the bulb using wires
shown in fig. Again, the bulb glows. Observe
the brightness of the bulb carefully.

What is the difference between the brightness
in two cases?

In the second case the bulb glows brightly.
Why does it happen? Explain.

Exercise

1. Answer these questions.

a) What are the effects of electric current?

b) What do you understand by a heating element? What principle is used in it? Name
two heating devices.

c) What do you understand by the filament wire? What are the two required
characteristics of the filament?

d) Why is nichrome wire used to prepare heating coils?

e) Why is a tungsten wire used as a filament in a glass bulb?

f) Why does a glass bulb contain inert gas like argon?

g) What are the three differences between current produced by dynamo and that
produced by battery?

h) Why are mica sheets used within an electric iron?

i) Why does a solution of sodium chloride conduct electricity but a solution of sugar
does not?

Blooming Science Book 10 109

j) Describe the working of electric bell.

k) How did Oerested discover that magnetism could be produced by electric current?

2. Answer the following questions.

a) What do you mean by electromagnetic induction? What is induced current?

b) State Faraday’s law of electromagnetic induction.

c) What is meant by direct and alternative current? A.C. current n Nepal is of 50Hz.
What does it mean?

d) What is a transformer? Give its principle.

e) What are the ways of increasing strength of electromagnets and emf in generator.

h) Why should earthing be provided to an electric iron?

i) Define 1kwh. What is solar cell? Write its applications.

3. a) A generator converts one form of energy into another. Name two forms of energy.

b) The structure of generator is shown in diagram, answer the questions based on it.

i) Lable 'A', 'B', 'C' and 'D' with one BA
function of each.

ii) On what principle is it based? D
C
iii) What happen when 'B' is rotated faster
in the brightness of bulb and why?

bulb

d) In the figure, N and S are compass needles and current is flowing in the circuit

shown. The deflection in the needle is shown in figure below. Battery

i) Copy the figure and show the direction of the current.

ii) What is the cause of the deflection of the magnetic S N
needle?

e) Complete the diagram of a step down transformer shown in Input

figure.

Core

110 Blooming Science Book 10

f) Study the figure and answer the questions.

i) name the device.

ii) Lable 'X' and 'Y' with one function of each.

iii) When wheel is rotated why does the bulb glow?

iv) What happens in brightness of bulb when speed of X
wheel is increased? Why? Y

g) Figure shows a common electrical appliance.

i) What is the name of this appliance?

ii) Name the parts labeled A and B? A B
Output AC
Input AC

iii) What is the part C? What is it made of?
Why is it laminated?

iv) Give at least one application of the device C
represented here.

h) What do you mean by MCB? Write 5 important roles that should be followed for
household wiring and three hazards of electricity.

i) When electric current is passed through tungsten filament, it glows with bright light
due to heating but it does not happen in other parts. Explain.

4. What is inverter? Write its uses.

5. Write short notes:

i. Adaptor ii. Charger iii. Bicycle dynamo iv. Inverter

6. Differentiate between
a) Filament lamp and fluorescent lamp.
b) A.C. and D.C.
c) Step up transformer and step down transformer.
d) Nichrome and tungsten

7. Give reasons:
a) Filament is made thin and long
b) We should use colour code in house wiring
c) Fluorescent lamp of 40w power is more efficient than 40w of filament lamp.
d) The number of turns in primary coil and secondary coil of transformer is not made
equal.
e) The use of a.c. current would be limited if the transformer was not invented.

Blooming Science Book 10 111

8. Solve the following numerical problems

a. A transformer has 2000 turns on the primary coil. The voltage applied to the primary
coil is 240 V. How many turns should there be in the secondary coil if the output voltage
is 48V?

[400 turns]

b. A transformer steps down the main supply from 240V to 120V to operate a 120V lamp.

i. What is the turn ratio of the transformer windings? nn12 = 2
1

ii. How many turns are there on the primary if the secondary has 100 turns? [ 21, 2000 turns]

c. A transformer operates from 210 volts a.c. supply to give an output of 12 V for an electric
appliance. If the secondary coil has 20 turns, calculate the turns in the primary coils?
[450 turns]

d. A university hostel has 300 lamps installed. The lamps consume 50 watts each

and lighted for 6 hours daily for 9 months. Calculate the total cost of electricity if the

price of electric energy is Rs. 5 per unit. [Rs. 121,500]

e. In a house there are 20 bulbs each of 100 watts, which is used 6 hours daily. There

are two electric irons each of 750 watts which is used one hour daily. Calculate the

total cost charged by the Nepal Electricity Board after 3 months if the price of the

electricity is Rs. 6.50 per unit. [Rs. 7897.5]

f. If a 2 KW electric heater is used for 10 hours for 15 days, and if electricity cost is Rs 5 per

kwh, calculate the total cost. [Rs. 1500]

g. A lamp is marked 240V, 60W. If electrical energy costs Rs. 6 per unit, what will be the cost

of running 6 such lamps for 5 hours a night for a month. [Rs. 324]

h. If two irons with 750 watt each are used 8 hours a day, how much tariff should be paid in

a month if cost of 1 unit of electricity is Rs 7. [Rs. 2520]

i. A transformer is used to play a radio of 12V. If the transformer is connected to 220V Ac

main and the number of turns of primary coil is 2200. Calculate number of turnings in

secondary coil. [120 turns]

j. A transformer has primary turns 3 times less than that of secondary coil. If voltage supply

is 220v, calculate secondary volate. [660v]

112 Blooming Science Book 10

9. Choose the correct alternatives from the following options.

i. Heating element used in electric heater is:

a. Chromium b. Nickel

c. Nichrome d. Tungsten

ii. Full form of LED is:

a. Light emitting Diode b. Light emitting Doll

c. Light energy Diode d. Long emitting Diode

iii. Which gas is filled in filament bulb?

a. Oxygen b. Hudrogen

c. Nitrogen or Argon d. All of the above

iv. Electromagnets is a:

a. Permanent magnet b. Temporary magnet

c. Circular magnet d. Loadstone

v. In which principle is transformer based?

a. Lighting b. Heating

c. Magnetic d. Mutual indication

Blooming Science Book 10 113

Chapter Classification of
Elements
7

Dmitri Mendeleev
1834 AD-1907 AD

Learning Outcomes Estimated Periods: 4

On the completion of this unit, the students will be able to:
 describe periodic law and explain the features, merits and demerits of Mendeleev and

Modern Periodic Table.
 define groups and periods.
 define valance electrons on the basis of atomic structure.
 explain the position of different elements in the periodic table.
 describe reactivity of metals and non-metals in periodic table.

Introduction

In the early stage of development of science, only the few elements were known so it was
not difficult to study the elements individually. In the 19th century, several new elements were
discovered. So chemists felt that elements should be classified. The early attempt to classify
the elements involved dividing them into metals and non-metals. This was based on certain
distinctive physical properties such as hardness, malleability, luster etc. But in this classification,
there was no place for the elements having properties of both metal and non-metals. Later metals
were further classified as alkali metals and alkaline earth metals. Such classification was based
on their particular chemical properties.

With the discovery of a large number of elements, the classification of elements became necessary
for the following reasons:

(a) Classification makes the study of properties of elements easy.

(b) The study of the properties of all the elements individually is difficult.

(c) The study of the properties of a typical element of a particular class enables us to assess
the properties of other elements of that group.

Mendeleev’s Periodic Law
D’mitri Mendeleev a Russian chemist, arranged the elements in the order of increasing atomic
masses. He found that the elements with similar properties occur at regular interval based
on studied the chemical properties of all elements known at that time. He formulated a law
of classification of elements known as Mendeleev’s periodic law. According to Mendeleev’s
periodic law: ‘‘The physical and chemical properties of elements are the periodic function of
their atomic weights.’’
Mendeleev arranged all the elements known at that time into horizontal rows and vertical
columns. The horizontal rows of elements are called periods and vertical columns are called
groups. The elements with similar properties came within the same group.

114 Blooming Science Book 10

The arrangement of the elements in the order of increasing atomic weight into groups and periods
is known as Mendeleev’s periods table

Portion of Mendeleev’s Periodic Table

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

Period H
1 1

Period Li Be B C N O F
2 7 9 11 12 14 19 19

Period Na Mg Al Si P S Ci
3 23 24 27.5 28 31 32 35.5

K Ca * Ti V Cr Mn Fe Co Ni
39 40 44 48 51 52 55 56 58 59
Period Cu Zn * * As Se Br
63 65 68 96 80
4 72 75

Rb Sr * Zr Nb Mo * Ru Rh Pd
85 87 88 90 94 96 100 104 104 106
Period Ag Cd In Sn Sb Te I
5 108 112 113 118 122 125 127


Cs Ba La Hf Ta W Re Os Ir Pt
Period 55 56 57 72 73 74 75 76 77 78
Au Hg Ti Pb Bi Po At
6 79 80 81 82 83 84 85

Only 63 elements were known at that time.

In Mendeleev’s periodic table, there were eight groups and seven periods. Mendeleev allowed
one group for the triads (Fe, Co, Ni; Rh, Os, Lr, Pt). There was no zero group in Mendeleev’s
original periodic table. Mendeleev left some gaps for the elements not known that time. The
missing elements of Mendeleev’s periodic table were discovered later on and their properties
were found to be very close to those predicted by Mendeleev. The elements scandium, gallium
and germanium were not known till 1871 A.D but their existence was perdicted by Mendeleev.
He named these elements as eka - boron, eka aluminum, etc.

Merits of Mendeleev’s Periodic Table

1. Systematic study of the elements: The Mendeleev’s classification condenses the study of
63 known elements and he left a provision for many more to the study of only 8 groups
of elements. We can have an idea of the properties of an element and its compounds by
knowing the group it belongs to. The properties of different elements of different groups
also can be compared.

Blooming Science Book 10 115

2. Prediction of new elements: At the time many elements were not discovered and he
left gaps in his table for new elements. Asserted that new elements will be discovered
ultimately to occupy the gaps in the Mendeleev’s periodic table.

3. Correction of certain doubtful atomic weights: Mendeleev found atomic weight of some
elements appeared to be doubtful in the periodic table. He gave right positions by studying
properties of such elements. The atomic weight of elements like beryllium (Be), platinum
(Pt), etc. were corrected.

Demerits of Mendeleev’s Periodic Table:

Mendeleev’s periodic table has the following defects

1. Hydrogen resembles both group I elements and group VII elements. It can loose one
electron as like the elements of I and can gain one electron as the elements of VII to
become stable. Thus the position of Hydrogen was not properly defined.

2. Some dissimilar elements have been placed in the same group. For example, copper,
silver and gold have been placed together in group I along with alkali metals. Similarly,
manganese (Mn) is placed in the group VII of the halogens

3. Three elements have been placed in the same group VIII. For example. Fe, Co and Ni are
placed in group VIII.

4. On the basis of periodic law, isotopes of an element must have separate place in the
periodic table. But there is no place for isotopes.

5. Lanthanides and actinides do not have proper place in this periodic table.

6. When the elements are arranged in the order of increasing atomic weights, the elements
with lower atomic weight should come first and the elements with higher atomic weight
should come later. But certain elements with higher atomic weight have been placed in
front of the element with lower atomic weight. For example, argon with atomic weight of
40 is placed after potassium whose atomic weight is 39.

Modern Periodic Table

Mendeleev’s periodic table was based on atomic weight. In 1913AD Henery Moseley found that
the atomic number is the more fundamental property of an element. The atomic number is taken
as the basis of classification of elements. This led to the formulation of Moseley’s periodic law.
This means that if the elements are arranged in order of their increasing atomic number, then
elements with similar properties are repeated after a regular interval.

Modern periodic law states that, ‘the physical and chemical properties of elements are the
periodic functions of their atomic numbers’.

By choosing atomic number as the basis of classification, the anomalies in the original
Mendeleev’s periodic table got removed, as described below.

116 Blooming Science Book 10

MODERN PERIODIC TABLE

eg. for hydrogen, Atomic number - 1 gas -

Symbol - H liquid -

Atomic weight - 1.008 synthetically made -

s Block p Block
Metals Non-metals

Groups 1 2 13 14 15 16 17 18
Periods IA IIA IIIA IVA VA VIA VIIA O

1 H1 B5 C6 N7 He2
1.008 10.881 12.011 14.007 4.003

Li3 Be4 d Block Al13 Si14 P15 O8 F9 Ne10
9.012 26.982 28.086 30.974 15.999 18.998 20.183
2 6.939 3 456 78 9 10 11 12
IIIB IVB VB VIB VIIB VIII IB IIB Ga31 Ge32 As33
Blooming Science Book 10 117 3 Na11 Mg12 69.72 72.59 74.922 S16 Cl17 Ar18
22.99 24.312 Sc21 In49 Sn50 32.453 35.453 39.948
44.956 114.82 118.69 Sb51
4 K19 Ca20 Ti22 V23 Cr24 Mn25 Fe26 Co27 Ni28 Cu29 Zn30 Ti81 Pb82 121.75 Se34 Br35 Kr36
39.102 40.08 Y39 47.9 50.942 50.942 54.938 55.847 58.933 58.933 63.54 63.54 204.37 207.19 78.96 79.904 83.8
88.95 Bi83
5 Rb37 Sr38 Zr40 Nb41 Mo42 Tc43 Ru44 Rh45 Pd46 Ag47 Cd48 208.98 Te52 I53 Xe54
85.47 87.62 La57 91.22 92.906 95.94 99.0 101.07 102.905 106.40 107.87 112.4 127.6 126.904 131.3
138.91
6 Cs55 Ba56 Hf72 Ta73 W74 Re75 Os76 Ir77 Pt78 Au79 Hg80 Po84 At85 Rn86
Ac89 178.49 180.943 183.85 186.2 190.2 192.2 195.09 196.967 200.59
132.905 137.34 227 210 210.0 222.0
Ku104 Ha105 Unh106 Uns107 Uno108 Une109 Uun110 Uuu111 Uub112
7 Fr87 Ra88 259 260 261 263 264 266 269 272 277
226
223

Lanthanides Ce58 Pr59 Nd60 Pm61 Sm62 Eu63 Gd64 Tb65 Dy66 Ho67 Er68 Tm69 Yb70 Lu71 f Block
Actinides 140.12 140.907 144.24 147 150.35 151.96 157.25 158.924 162.5 163.94 167.24 170.61 173.04 174.97

Th90 Pa91 U92 Np93 Pu94 Am95 Cm96 Bk97 Cf98 Es99 Fm100 Md101 No102 Lr103
232.036 231 238.03 237 242 243 247 249 251 254 253 256 259 260

Inversion in Mendeleev’s Table

The anomaly of having higher atomic mass elements before the elements with lower atomic
mass is removed. For example, the atomic number of Ar is 18 and that of K is 19. Although
the atomic mass of Ar is higher than that of K.

Position of Isotopes

Isotopes are those elements which have same atomic number but differing in atomic
weights. Although isotopes of an element have different atomic masses, they have same
atomic number. Hence, the isotopes should be given the same place in the table.

Features of the Long Form of Periodic Table (modern period table)

The general features of the long form of periodic table are:

a. The elements are arranged in order of their increasing atomic number.

b. It has seven horizontal rows called periods. Some periods are short while others are long.

The first period has only two elements, Hydrogen and Helium and is called very short period.
The second and third periods have eight elements in each and are called as short period. The
fourth and fifth have 18 elements in each and called as long period. The sixth period has 32
elements and called as very long period. The seventh period is still incomplete.

Periods in the long form of periodic table

Period Total First element of the Last element of Size
period the period
First 2 Helium (2) Very short
Second 8 Hydrogen (1) Neon (10) Short
Third 8 Lithium (5) Short
Fourth 18 Sodium (11) Argon (18) Long
Fifth 18 Potassium (19) Krypton (30) Long
Sixth 32 Rubidium (37) Xenon (54)
Seventh 23 Caesium (55) Radon (86) Very Long
Francium (87) Ennum (109) Incomplete

c. It has 18 vertical columns called groups. So, there are 18 groups only. The vertical columns
are numbered as IA, IIA, IIIA, IVA, VA, VIA, VIIA, IB, IIB, IIIB, IVB, VB, VIB, VIIB in
addition to VIII group and the zero group.

d. The elements have been clearly separated as normal, transition and noble. Metals and non-
metals are also separated.

e. The subgroups A and B are clearly separated and treated as separated group A and group B
because elements belonging to group A differ in properties from elements belong to group B.

118 Blooming Science Book 10

Position of different types of elements in modern periodic table

a. Elements belonging to sub-group A are normal representative elements. Their outermost
shell is incomplete and other inner shells are completely filled with electrons. Elements of
sub-group IA are called alkali metals because their hydroxide are highly soluble in water.
Lithium, sodium, potassium are alkali metals.

b. Element of sub-group IIA are called alkaline earth metals. Beryllium, magnesium and
calcium are alkaline earth metals. These metals dissolve less in water to form alkali.

c. Elements of group VIIA are called halogens because they form salt with IA elements
example Nacl. Fluorine, chlorine and bromine are halogens.

d. Elements of group O are called noble or inert gases as their valence shell is completely
filled and does not take part in chemical reaction. This group is placed in extreme right of
the periodic table.

e. Elements with atomic number 57 to 71 are called lanthanides. Elements with atomic
number 89 to 103 are called actinides. These are the radioactive elements.

Lanthanides and actinides are two series of inner-transition elements, each having 14
elements. They are also known as f-block elements because the series of elements in
which 4f-orbital (sub-shell) are progressively filled. These two series of f-block elements
are placed at the bottom of two separate rows. All the elements of each series of f-block
have similar properties, whereas the actinides include the radioactive elements.

f. Position of metals, non-metals and metalloids: Elements are classified as metals, non-
metals and metalloids on the basis of their properties.

In the table, a complete separation of metals and non-metals is done. The elements left of
the staircase line are mostly metals while those on the right of it are non-metals some of
the elements that lie right next to the staircase line posses properties intermediate between
those of metals and non-metals are called metalloids. These are boron (B), silicon (S),
arsenic (As);antimony (Sb) germanium (Ge) etc.

Merits of Modern Periodic Table

The long form periodic table has the following merits:

1. Modern periodic table is based on the atomic number of elements which is the most
fundamental property of the atom.

2. It explains clearly, why elements in a group shows similar properties. It also explains why
elements of a group differ in properties from the elements of other groups.

In the modern periodic table, elements are arranged in accordance with their electronic
configurations. The elements having similar electronic configuration (same valence
electrons) are placed in same group. Hence, elements in a group show similar properties.
Elements with different electronic configuration are grouped separately, hence they show
different properties.

3. It gives satisfactory explanation about the chemical periodicity in the properties of
elements. The periodicity in properties arises due to periodicity in electronic configuration
of elements.

Blooming Science Book 10 119

4. It removes all the anomalies, e.g. the position of isotopes, wrong order of atomic masses
of some elements, etc. of Mendeleev’s periodic table.

5. It explains some what about the position of hydrogen. As hydrogen has least atomic
number, it is placed in group IA.

6. Lanthanides and actinides were placed at bottom of periodic table as elements in these
series have similar chemical properties.

Defects

Though many of the defects of Mendeleev’s periodic table have been removed in the modern
periodic table has the following defects.

1. Position of hydrogen is still controversial. Hydrogen is an electropositive s-block
element. It is placed in group IA of the modern periodic table. But it also has some
relation with the VIIA group elements.

2. Position of Helium: On the basis of the electronic configuration, helium should have
placed in group IIA along with the alkaline earth metals. But this element has been placed
in group zero with the noble gases.

Characteristics of Groups

A vertical column in the periodic table is called a group. All elements in a group show similar
chemical properties. There is however, a gradual variation in the physical properties of the
elements in a group.

The group of the element is identified by its valence electron in representative elements, eg.
valence electron of oxygen is 6, so it is in group VI A. Group = No. of valence electron. Elements
in a group show the following characteristics.

1. Valency

All elements in a group generally have the same valency. The valency of all the elements is
determined by the number of valence electrons. Following table shows the valencies of the
elements belonging to different groups.

Group No. I II III IV V VI VII 0

Element Li Be B C N O F Ne

No. of valence 1 2 3 4 5 6 7 8
electron

Valency 12343210

In general, Valency of metal =Number of valence electrons.

[Valency of non-metal = 8-Valence electrons]

This rule does not apply to transition elements. Hydrogen is a non-metal but its valency is equal
to its group number i.e.l. Noble gases are also non-metals but the valency is zero.

120 Blooming Science Book 10

2. Atomic Size or Atomic Radius H

On moving downwards in a group, the size of the atom increases.

On moving down the group, in each new element a new shell of electrons is
added to the atom. This increases the size of the atom of each new element
down the group.

Table: Atomic radius increasing down in group. Li

IA VIIA 11P

Li [2,1] F [2,7] 12N

Na [2,8,1] Cl [2,8,7]

K [2,8,8,1] Br [2,8,18,7]

Na

3. Chemical Reactivity

All the elements of a group have similar electrogyrations i.e. same valence electrons. Hence
their chemical properties are similar. However, chemical reactivity shows a regular gradation in
moving down a group.

a. Reactivity in metals

The chemical reactivity of metals increases on moving down a group. For example, lithium
is the least reactive while francium is the most reactive among the elements of group IA. It is
because on moving down a group, atomic size increases. The valence electrons thus, are far away
from the nucleus. The force between the nucleus and the valence electrons becomes weaker and
weaker. Due to this, the atom can lose its valence electrons easily to form positive ions. Hence,
on moving down in a group, the tendency to lose electrons increases, that is, electro positivity
increases. For example, the electropositive character of sodium is more than that of lithium and so
on. So reactivity increases down in the groups in metals.

b. Reactivity in non-metals

The chemical reactivity of non-metals decreases on moving down a group. For example, fluorine
is chemically the most reactive and iodine is the least reactive in group VIIA.

On moving downward in a group the atomic size increases. As the atomic size increases, the force
with which the nucleus is able to attract the electrons decreases. As a result, elements having
bigger atomic number have less tendency to gain electron. i.e. electro negativity decreases in
moving down a group. For example, in elements of group VIIA, fluorine has the highest electro
negativity ie. it can gain electron easily then iodine. So, fluorine is more reactive than iodine.

Periods

A horizontal row of elements in the periodic table is called a period. There are seven periods in
modern periodic table. Each period starts with group IA and ends up with group 0. Each period
starts with an element in which a new shell starts getting filled with an electron, and ends up with
a noble gas which has all the inner and outer shells completely filled. Elements in the period
show the following characteristics.

Blooming Science Book 10 121

1. Valence Electrons

In moving left from to the right in a period, the number of valence electrons increases from 1 to
8. In the first period, the number increases is from 1 to 2 only.

Change in Number of Valence Electrons in a period

Third period 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
Electronic
configurations 1 2 3 4 5 6 7 8

No. of Valence
electrons

Valency

In short periods valency with respect of hydrogen increases from 1 to 4 and then decreases from
4 to 1 on moving from left to right.

Table - Change in Valency
Third period
Valencies Na Mg Al Si P S Cl Ar
2 10
12343

Thus elements in the same period have different valencies.

2. Atomic size

Atomic size of element decreases from left to right in a period. In a period the atomic number
increases from left to right. This means that, the number of protons and electrons increases.
The added electron enter the same shell. The increased positive charge in the nucleus attracts
the electrons towards the nucleus with greater attractive force. As a result, the electronic shell
shrinks and therefore the atomic size decreases.

Group IA IIA IIIA IVA

3rd Period

[2, 8, 1] [2, 8, 2] [2, 8, 3] [2, 8, 4]
Na Mg Al Si

3. Chemical reactivity

The reactivity of elements decreases from left to right in period (from group IA to IIIA) as these
are electropositive elements and their reactivity is the tendency of losing electrons. It is more
difficult to check out more electrons from the outermost orbit. Similarly reactivity increases
from groups IVA to VIIA when going left to right the period as these are electronegative elements
and their reactivity is the tendency of gaining electrons. It is more easier to to gain less number
od electrons for the outermost.

122 Blooming Science Book 10

Sub Shell and Electronic Configuration

The electrons present in the outermost orbit of the atoms are called valence electrons. Inert gases
are very stable and hardly enter into any chemical reactions. In each (except helium which has
two electrons), the outermost orbit contains eight electrons (octet). The chemical stability is due
to the presence of these eight electrons in the outermost orbit. The space around the nucleus
where the probability of finding electron is maximum is called sub shell or orbitals.

The study of long form of periodic table shows that the physical and chemical properties are
governed by the number and arrangement of orbital electrons, which is again based in the atomic
number. If the elements with similar electronic configurations in their orbitals are arranged in
the same group, the elements within a group will show similarities in physical and chemical
properties. Based on this concept, the long form of the periodic table can be devided into blocks
of elements depending upon the orbital electronic configurations. This sequence of filling of
electrons leads to another form of groupings. The elements are referred to s-block, p-block,
d-block and f-block elements according to respective electrons filled in the s, p, d, f. orbitals in
the atom of the elements. The pattern of electrons in orbital’s is showing in the table below.

Electronic Configuration of Some Elements

Symbol Atomic K LM N O P Q
No. 1s 6s 6p 6d 6f 7s
2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f

H11

He 2 2

Li 3 2 1
2
Be 4 2 21
22
B52 23
24
C62 25
26
N72 26 1
26 2
O82 26 21
26 22
F 92 26 23
26 24
Ne 10 2

Na 11 2

Mg 12 2

Al 13 2

Si 14 2

P 15 2

S 16 2

Blooming Science Book 10 123

Cl 17 2 2 6 2 5

Ar 18 2 2 6 2 6

K 19 2 26 26 1

Ca 20 2 2 6 2 6 2

Fe 26 2 2 6 2 6 6 2

Ni 28 2 2 6 2 6 8 2

Cu 29 2 2 6 2 6 10 1

Ag 47 2 2 6 2 6 10 2 6 10 1

Sn 50 2 2 6 2 6 10 2 6 10 22

Ba 56 2 2 6 2 6 10 2 6 10 26 2

Pb 82 2 2 6 2 6 10 2 6 10 14 2 6 10 2 2

U 92 2 2 6 2 6 10 2 6 10 14 2 6 10 3 2 6 1 2

s-block elements

Elements of the group I A and II A constitute s-block elements. Group I A has one electron in their
outermost orbit in ns1 where n stands for the principal quantum number and s for orbital. It is the
pattern of filling of electrons in the orbitals. Group II A elements (Be to Ra) have two electrons in
the s-orbital of the outermost orbit. The general electronic configuration of the outermost orbit is
ns2.

p-block elements

Elements of the groups IIIA, IVA, VA, VIA, VIIA and 0 constitute p-block elements. The general
electronic configuration of the outermost orbits of these elements ns2,np1 to ns2,np6.

In these groups, their s-orbital’s are complete, all have their outermost p-orbital being progressively
filled up with one electron at a time. Because their properties are dependent on the presence of
p-electrons, they are called as p-block elements.

d-block elements

Elements of the group IB, IIB, IIIB, IVB, VB, VIB, VIIB, VIII, belonging to the fourth, fifth,
sixth and incomplete sixth periods are known as d-block elements. They have two outermost
orbital incomplete. Their properties are midway between those of s-block and p-block, they are
called transition elements.

f-block elements

Elements of this block have three outermost orbital’s incomplete. There are series of f-block
elements (a) Lanthanides from La (At No. 57) to Lu (At No. 71) and Actinides from Ac (At No. 89)
to Lr (At No. 103).

Here the filling of electrons takes place in the f- orbital’s of the atoms of each element, and hence
are known as f-block elements. These two series of elements are similar in chemical behavior and
are not accommodated in the conventional periodic table.

124 Blooming Science Book 10

Electronic configuration in terms of sub-shells: Aufbau principle explain the sequence of
filing of various orbitals by electron which is shown below. Each orbit or shell has orbital or
sub-orbital s, p, d and f and orbital’s can gave only 2, 6,10 and 14 electrons respectively.

1s

2s 2p

3s 3p 3d

4s 4p 4d 4f

5s 5p 5d 5f

6s 6p 6d

7s 7p

⇒ 1s 2s 2p 3s 3p 4s 3d 4p


6p 5d 4f 6s 5p 4d 5s



7s 5f 6d 7p

So, the sequence of filling electrons in orbitals is; 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s,
4t, 5d, 6p, 7s, 5f, 6d, 7p.

But for class 10 students are required to know up to the followings

[1s 2s 2p 3s 4s 3d 4p]

Two exceptional cases

Chromium (Cr) = 24 ⇒ 1s2 2s2 2p6 3s2 3p6 3d4 4s2 (Real configuration)

= 1s2 2s2 2p6 3s2 3p6 3d5 4s1 (stable configuration)

Copper (Cu) = 29 = 1s2 2s2 2p6 3s2 3p6 3d9 4s2 (Real configuration)

= 1s2 2s2 2p6 3s2 3p6 3d10 4s1 (stable configuration)

Activity -1

To show the electronic configuration of first 20 elements.

Write down the orbital configuration of elements from Atomic number 1 to 20 in your
project work copy. Classify them into metals, non metals and metalloids s-block and
p- block elements, etc.

Blooming Science Book 10 125

Let's Learn

1. The element of groups IB or VII B and VIII are called transition elements. They lie in
between sub-group IIA and IIIA. They are also called d-block elements because elements fill
the valence shells of atom having d-sub shells one by one as the atomic number increases.

2. Elements of group IA (Li, Na, K, Rb, Ce, Fr) are known as reactive metals because they
all have single valence elements due to which they can easily loose single electron to other
electron to become stable.

3 Elements of group VII A (F, Cl, Br, I) electrons known as reactive non-metals because
they all have seven valence electrons due to which they can easily gain single electrons
from other to become stable.

4. Lanthanides and actinides are f-block elements and they are also called inner-transition
elements because they fall in between III ‘B’ and IV ‘B’ group of periodic table.

5. Reactivity increases from left to right in the period from group IVA to VIIA. It is because
the atomic size decreases while moving left to right in period which increases the tendency
of gaining electron by non-metal in right side than in left side. So, reactivity increase left
to right in period.

6. Reactivity decreases left to right in period from group IA to IIIA it is because the atomic
size decreases while moving left to right in period which decreases the tendency of loosing
electron by metals in this group, i.e. metals in the right side have less chance of loosing
electron than that in left side.

Points to Remember

1. The total number of elements discovered are 109 of which 92 are natural and 17 are artificial.
2. Only 63 elements were known during Mendeleev’s time. He arranged the elements into rows

and columns based in the increasing atomic weights, which are called the groups and periods.
3. Mendeleev’s periodic law stated that “the physical and chemical properties of the elements

are periodic function of their atomic weights’’.
4. Modern periodic law stated that “the physical and chemical properties of elements are the

periodic functions of their atomic number.” This law was formulated by Moseley.
5. On proceeding from left to right of the table, atomic number successively increases.
6. The periodicity is due to recurrence of similar types of electronic configurations in the

outermost shell.
7. The members of group IA are called alkali metals. These metals have one electron in the

outermost shell.
8. Inert gases are kept in zero group. They have no valency.
9. Non-metals occupy the right hand corner of periodic table and metalloids between

elements of group I and VII.
10. The tendency to lose electron increases from top to bottom in a group.
11. The tendency to gain electron increases with decreases in size.
12. Fluorine is the most reactive non-metal.
13. The shells K, L, M, N…. around the nucleus have orbital’s or sub-shells.
14. There are four types of orbital’s called s, p, d and f. s orbital can fill 2 electrons, 6 electrons

in p, 10 electrons in d and 14 electrons in f.

126 Blooming Science Book 10

15. The elements are said to be in s-block if valence electrons fill the s-orbital and in p- block
in case electrons go on filling the p orbital’s and so on for d and f blocks.

16. Actinides and Lanthanides are called inner transition elements also.

Project Work
Make your own periodic table by using a chart paper and coloured pens. Use different
coloured pen for metals, non-metals, metalloids, transition metals, lanthanides and actinides.
Show the period table to your teacher and paste it in your classroom or study room.

Exercise

1. What is Mendeleev’s periodic law? Write the merits of Mendeleev’s periodic table.
2. What were the defects in Mendeleev’s periodic table?
3. Why did Mendeleev leave many gaps in his periodic table?
4. How many elements were known at the time of Mendeleev? Name one element which was

not known at the time of Mendeleev, but when discovered later found to have the same
properties as predicted by Mendeleev.
5. State modern periodic law.
7. What is a modern periodic table? Mention the special features of Modern periodic table.
8. Write three differences between the Mendeleev’s periodic table and the modern periodic
table.
9. Why are lanthanides and actinides placed separately in the Modern periodic table?
11. Why is hydrogen placed both in first and seventh group in the periodic table? Give one
reason for each.
12. What are inert elements? In which group are they placed and why? Define sub shells.
13. What are transition elements? Where are they placed in the periodic table? What determine
their valencies?
14. How do the metallic characters change in a period from left to right in the modern periodic
table?
15. Write the group and period of nitrogen and oxygen. Why is oxygen more reactive than
nitrogen? Explain.
16. The atomic sizes increase on moving downwards in a group. What affects the size of an
atoms in the reactivity of elements?
17. What are alkali metals? Where are they placed in the periodic table?
18. State one reason for placing chlorine and bromine in the same group in the periodic table.

Blooming Science Book 10 127

19. Write the sub shell electronic configuration of potassium, lithium, fluorine and chlorine.
From these electronic configurations explain why potassium is more reactive than lithium
and fluorine is more reactive than chlorine?

20. Distinguish between:

i. Groups and periods

ii. s-block and p-block elements

iii. Lanthanides and actinides

iv. Halogens and alkali metals

v. Transition and representative elements

21. Study the given parts of modern periodic table and answer the questions.

i. Write the common name of given groups with a reason.

ii. Write their groups with a reason.

iii. Which one is more reactive element in ‘X’ and ‘Y’ respectively? Explain.

22. Study the sub shell configuration of elements and answer the questions.

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

B = 1s2 2s2 2p4

C = 1s1

i. Write the periods and groups of ‘A’ and ‘B’.

ii. What is the valency of A and B?

iii. Write the name and molecular formula of compound formed by A and B.

iv. Which one is less reactive between A and C? Why?

23. Choose the correct alternatives from the following options.

i. Group IA elements in modern periodic table are called:

a. Halogens b. Alkali metal

c. Alkaline earth metal d. All of the above

ii. The number of maximum electrons in ‘P’ orbital are:

a. 2 b. 4

c. 6 d. 8

iii. In metals, if we go down in group, reactivity :

a. Increases b. Remains same

c. decreases d. None of the above

iv. Moving left to right in the period the atomic size:

a. Remains same b. Increases

c. Decreases d. None of the above

v. Transition elements belong to in which block of modern periodic table?

a. f b. p

c. d d. s

128 Blooming Science Book 10

Chapter Chemical Reaction

8

Learning Outcomes Antoine Lavoisier
1743 AD-1794 AD

Estimated Periods: 5+2

On completion of this unit, the students will be able to:
 describe about different types of chemical reactions.
 write chemical reactions in the form of chemical equations.
 eplain factors of chemical reaction.
 differentiate endothermic and exothermic reaction.

Introduction

The transformation of a substance from one form to another form permanently is called chemical
reaction. This permanent change may be due to combination, decomposition, displacement
or rearrangement of molecules of a substance. The chemical reaction can be represented by
chemical equation. There are two types of chemical equations called word equation and symbolic
equation.

The properties of matters depend on the organization of their molecules. Although the same atoms
are present in a chemical reaction before and after the reaction, different types of molecules are
formed as a result of the reaction.

Chemical reaction is represented in the form of an equation. The elements or compounds in
which the chemical reaction occurs are called reactants and left written on the left hand side of
an arrow (→) and the elements or compounds that are formed as a result of reaction are called
products and written on the right hand side of the arrow. The direction of arrow indicates the
reactants and the products.

Reactants Products

The condition of the reaction in which it occurs is sometimes or when necessary written in short
above the arrow.

For example: Water Electricity Oxygen + Hydrogen
Mercuric Oxide Heat Mercury + Oxygen
Potassium Chlorate Heat Potassium Chloride + Oxygen

The equation represented by the name of the chemical substances in words instead of molecular
formula is called word equation. The equation of chemical reaction expressed in short form by
a chemical formula is called symbolic equation or formula equation. The examples given above
are word equations and equation given below are formula equations.

Blooming Science Book 10 129

H2O ∆ H2 + O2
HgO ∆ Hg + O2
KClO3 ∆ KCl + O2

Balanced Chemical Equation

The chemical reactions are represented by the chemical equations using chemical formula or
molecular formula instead of words. The equation written by balancing the number of atoms of
elements on both sides of the reactants and products is called balanced chemical equation.

Method of writing balanced chemical equation

It is necessary to remember the following points while writing balanced chemical equations:

1. First of all the chemical reactions should be represented correctly in the form of word
equation. For example:

Hydrogen + Oxygen Heat Water

(Reactants) ( Product)

2. Every element or compound that takes part in and is produced from the chemical reaction

should be represented in the form of molecular formula.

H2 + O2 Heat H2O

3. Then, the number of atoms on either side should be made equal without disturbing the
molecular formula.

2H2 + O2 Heat 2H2O

(The digit used for multiplying the molecule indicates its number. For example 2H2O means two
molecules of H2O)

While balancing the equation, the number should be added so that there is equal number of atoms on
either side of the arrow. This method of balancing the chemical equation is called hit and trial method.

Some other balanced chemical equations

(a) Potassium chloride and oxygen are formed on heating potassium chlorate.
(i) Word Equation: Potassium Chlorate Heat Potassium Chloride + Oxygen
(ii) Formula Equation: KClO3 Heat KCl + O2

(iii) The following balanced equation is formed by balancing the equation using digit to
represent the number of molecules without disturbing the molecular formula.

2KClO3 Heat 2KCl + 3O2

(b) Ammonia is formed by the combination of hydrogen and nitrogen at high temperature and
under pressure in the presence of a catalyst.

Word Equation: Nitrogen + Hydrogen Heat/Pressure Ammonia
Catalyst/Promoter

130 Blooming Science Book 10

Heat/Pressure
Formula Equation : N2 + H2 Catalyst/Promoter NH3

Balanced Equation: N2 + 3H2 Heat/Pressure 2NH3
Catalyst/Promoter

Symbols used to indicate the state

Symbols indicating solid, liquid, gas or aqueous solution are used in chemical reaction when
necessary. For example: Solid is indicated by (s), liquid by (l), gas by (g) and aqueous solution
by (aq). Likewise ∆ indicates heat, ↑ indicates gas and ↓ indicates precipitate.

These symbols are written beside elements or compounds. For example, the above reactions are

indicated as follows:

1. 2KClO3 (s) ∆ 2KCl(s) + 3O2↑ Scan for practical experiment

2. N2(g) + 3H2(g) Heat/Pressure 2NH3↑
Catalyst/Promoter

3. 2HgO (s) ∆ 2Hg (l) + O2↑ visit: csp.codes/c10e09
2NaOH (aq) + H2↑
4. 2Na (s) + 2H2O (l)
Types of Chemical Reaction

Chemical reactions are of different types. A few important types are given below:

1. Combination reaction.

2. Decomposition reaction.

3. Displacement reaction

(a) Single displacement reaction

(b) Double displacement reaction

4. Acid - base reaction

1. Combination Reaction

The chemical reaction in which two or more than two elements or compounds combine to
form a new compound is called combination reaction. This reaction is also called as addition
reaction. This type of reaction occurs due to heat, light, electricity, catalyst, pressure or direct
combining.

2Na(s) + Cl2 (g) 2NaCl (s)
Fe (s) + S (s) ∆ Fe S (s)

N2 (g) + H2 (g) 500oC/200 atm 2NH3 (g) + Heat energy

Fe / Mo

2 Decomposition Reaction

The chemical reaction in which molecules of a substance decompose into two or more than
two elements or compounds is called decomposition or dissociation reaction. This reaction is
also called as dissociation reaction This type of reaction occurs due to heat, light, electricity,
catalyst etc.

Blooming Science Book 10 131

For example: 2PbO2 (s) ∆ 2PbO (s) + O2 (g)
(a) By heat

240oC
2KClO3 (s) MnO2 2KCl (s) + 3O2(g)

(b) By electrolysis

2NaCl (s) 2Na (s) + Cl2 (g)

2H2O (l) 2H2 (g) + O2 (g)

Electrolysis of NaCl occurs at high temperature.

(c) By light

2AgBr (s) Light 2Ag (s) + Br2 (l)

6Co2 + 6H2O Light C6H12O6 + 6O2

(d) By catalyst MnO2 2H2O (l) + O2 (g)
2H2O2 (aq)

3. Displacement Reaction

The chemical reaction in which an element or a radical of a compound is displaced by another
element is called displacement reaction. This reaction is also called ae replacement reaction.
The displacement reaction is of two types.

(a) Single displacement reaction

In this reaction, only one element or a radical is displaced.

Zn (s) + H2SO4 (aq) ZnSO4 (aq) + H2 (g)

Zn (s) + CuSO4 (aq) ZnSO4 (aq) + Cu (s)

2KI (s) + Cl2 (g) 2KCl (aq) + I2 (g)

(b) Double displacement reaction

The chemical reaction in which an element or a radical of one compound is
mutually displaced by an element or a radical of another compound is called double
displacement reaction.

For example:

CaCl2 (aq) + 2AgNO3 (aq) Ca (NO3)2 (aq) + 2AgCl (s)
HgCl2 (aq) + 2KI (aq) 2KCl (aq) + HgI2 (s)

132 Blooming Science Book 10

(4) Acid-Base Reaction

The chemical reaction in which an acid reacts with a base to produce salt and water is
called acid base reaction.

For example:

HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)

H2SO4 (aq) + CaO (s) CaSO4 (aq) + H2O (l)

Such reaction is also known as neutralization reaction because the by-products are salt

and water which are chemically neutral.

Activity -1
To observe the chemical reaction between iron and copper sulphate solution.(Displacement
reaction)
Material required:
beaker, iron nail, copper sulphate solution.
Method:
i) Take some amount of copper sulphate solution in a beaker.
ii) Put an iron nail in copper sulphate solution for some time.
iii) Take out the pin from solution and observe.

Beaker

Copper sulphate solution

Iron nail coated by
copper

Observation:
1. What do you observe around the surface of nail?
2. What has happened? Write the chemical equation to show the reaction.
Result:
Copper is coated over the iron nail.
Conclusion:
Iron displaces copper from copper sulphate as iron is more electropositive than copper.

Fe + CuSO4 FeSO4 + Cu

Blooming Science Book 10 133

Factors affecting chemical reaction

There are different factors that affect the chemical reaction. Some of the important factors are
given below:

(a) By heat, electricity or light energy

Heat energy provides more dynamic energy to the reactant molecules. This increases
the capacity to reach by colliding with another molecule. The electrical energy helps the
ion move to oppositely charged electrodes, light energy makes the reactant molecules
more reactive and helps carry out the reaction faster. When calcium carbonate (CaCO3) is
heated, it is decomposed into calcium oxide (CaO) and carbon dioxide (CO2). Electricity
decomposes water into Hydrogen and Oxygen. Light decomposes silver bromide (AgBr)
into silver (Ag) and bromine (Br). Examples:

CaCO3 ▲ CaO+CO2
2H2O electricity 2H2O+O2
H2+Cl2 light 2HCl

(b) By simple contact

Some substances react when they come in contact with eachother. For example: when
iodine (I2) and phosphorous (P) come in contact, they react explosively. Similarly salt is
formed as soon as sodium is brought in contact with chlorine.

2Na + Cl2 2NaCl

(c) By dissolving

There is no reaction between solid sodium chloride (NaCl) and silver nitrate (AgNO3) but
when solutions of both of them are mixed, AgCl is precipitated.

NaCl (aq) + AgNO3 (aq) NaNO3 (aq) + AgCl

(d) By pressure

Fire cracker is exploded by pressure. Similarly, when pressure is applied on a mixture of
potassium chloride and sulphur, it explodes.

2KCl + S Pressure K2S + Cl2 (explosive reaction)

(e) By catalyst

Potassium Chlorate (KClO3) gives out oxygen at low temperature when manganese
dioxide (MnO2) is used as a catalyst.
2KClO3 360oC 2KCl + 3O2

2KClO3 240oC 2KCl + 3O2
MnO2

(f) Surface area

Larger the area of reactant, faster the reaction. It is because the probability of collision of
molecules increases which increases the rate of reaction.

134 Blooming Science Book 10

Catalyst

A catalyst is a substance which affects the rate of chemical reaction. In the above example MnO2
is a catalyst. The catalyst changes the rate of reaction but it remains unchanged. There are two
types of catalyst: negative and positive. The negative catalyst decreases the rate of a reaction. For

example, the use of glycerine decreases the rate of decomposition of hydrogen peroxide.

2H2O2 Glycerine 2H2O + O2. Phosphoric acid (H3PO4) is another example of negative catalyst.
2H2O2 MnO2 2H2O + O2. The positive catalyst increases the rate of a reaction. In the above
example, MnO2 is a positive catalyst.

Endothermic Reaction and Exothermic Reaction

The reactions in which heat is absorbed from the surrounding are called endothermic reactions.
The compounds formed by absorption of heat are called endothermic compounds. Some examples
of the endothermic reactions are as follows:

CaCO3 + heat CaO + CO2

2KClO3 + heat 2KCl + 3O2↑

N2 + O2 + heat 2NO

Nitric oxide

The reactions in which the heat energy is released to the surrounding are called exothermic

reactions. The compounds formed by exothermic reactions are called exothermic compounds.

Some examples of the exothermic compounds are carbon dioxide, water, slaked lime, zinc

chloride, etc.

C+ O2 CO2 + heat Scan for practical experiment

2H2 + O2 2H2O + heat

CaO + H2O Ca (OH)2 + large amount of heat

Slaked lime

Zn + 2HCl ZnCl2 + H2 + heat

Rate of Chemical Reaction visit: csp.codes/c10e10

Chemical reactions take place in varying rate. Some chemical reactions are so rapid that they
occur as soon as the reactants are mixed with each other. For example, when sodium reacts with
water, it gives hydrogen and sodium hydroxide. On the other hand, there are certain chemical
reactions which take place at an extremely slow rate. For example, rusting of iron occurs very
slowly, that one could be misled into thinking that no reaction is taking place at all.

The knowledge about the rate of a chemical reaction is essential from industrial point of views.
From industrial point of view it might be necessary to accelerate most of the reactions and some
others to slow down for careful control of some violently explosive reactions.

The rate of chemical reaction is defined as the change in concentration of any one of the reactants
or products per unit time to complete the reaction. The rate of chemical reaction depends upon
concentration, temperature, catalyst and the nature of the reactants. The rate of reactions can be
increased by increasing the concentration of reacting substances, by using catalyst, by increasing
temperature, by increasing the surface area of contact of the reactants, nature of reactants and

Blooming Science Book 10 135

products, by exposing to radiation, etc. Some of the above-mentioned factors that affect the rate
of any chemical reaction are as follows:

I. Temperature

In general, the increase in the temperature increases the rate of almost all chemical
reactions while decrease in temperature decreases the reaction rate. The increase in
temperature increases the kinetic energy of the molecules. It causes the breaking of bonds
in the reactant molecules and reaction takes place at a high speed. Generally, there is
double-fold increase in the reaction rate for each 10oC increase in temperature.

II. Concentration of reactant

The rate of reaction increases with an increase in the concentration of reactants. This
means that the rate of reaction is directly proportional to the concentration of the reactants.
For example, when dilute HCl is poured into a piece of calcium carbonate (CaCO3) there
is effervescence with the evolution of CO2. The effervescence is brisk when concentrated
HCl is added. So, it increases the rate of chemical reaction between CaCO3 and HCl. This
is because CaCO3 and HCl increases by decreasing their distance between the molecules.

III. Surface area

Larger the surface area, greater the rate of reaction. It is because the rate of collision of
molecules of reactants increases which increases the rage of reaction.

IV. The rate of reaction also depends upon the nature of atom.

For example, the elements like Li, Na, K, etc. belong to the group IA in the periodic table.
They are highly active metals because they have one electron in their valence shell. They
can give its valence electron easily to other during chemical reaction.

The group VIII or zero group elements like Ne, Ar, Kr etc. in the periodic table are inactive
or inert because they contain eight valence electrons in their valence shell.

Activity -2

To show the rate of chemical reaction:

1. Prepare a solution of 4 gm of sodium thio-sulphate (Na2S2O3) with 100 ml of water in a
beaker.

2. Prepare a solution of 20 ml of concentrated hydrochloric acid (HCl) with 100 ml of
water in another beaker.

3. Pour 30 ml of sodium thio-sulphate solution in a conical flask and add 20 ml of water
to it so the total volume of solution is exactly 50ml.

4. Place the conical flask over black ‘X’ sign made on the sheet of white paper.

5. Now, add 5ml of hydrochloric acid to the solution of the flask. Shake the solution
gently.

6. Notice that the reaction between Na2S2O3 and HCl begins and precipitation of sulphur
takes place.

7. Look through the flask and note the time taken that the black sign of ‘X’ disappears.
This disappearance of ‘X’ sign takes place due to the formation of sulphur’s
precipitation.

136 Blooming Science Book 10

8. In the same way, note the time taken at the time the sign black ‘X’ disappears in the
reaction between the following:

(a) 10 ml solution of Na2S2O3 + 40 ml of water and 5 ml HCl

(b) 20 ml solution of Na2S2O3 + 30 ml of water and 5 ml HCl

(c) 40 ml solution of Na2S2O3 + 10 ml of water and 5 ml HCl

(d) 50 ml solution of Na2S2O3 + 5 ml HCl

Observation: Note down the time taken to disapper the cross mark.

S.N. Volume of Na2S2O3 Volume Volume Total Time taken that made ‘X ’
solution of water of HCl volume sign invisible

1. 10 ml 40 ml 5 ml 55 ml

2. 20 ml 30 ml 5 ml 55 ml

3. 40 ml 10 ml 5 ml 55 ml

4. 50 ml - 5 ml 55 ml

Conclusion:

Draw your conclusion and write down in your copy.

Let's Learn

1. MnO2 is called a positive catalyst because it increases the rate of chemical reactions. It is
used in decomposition of hydrogen peroxide without heating to prepare oxygen gas.

2. Acid-base reaction is called neutralization reaction because the by-products of the reaction
are salt and water which are chemically inactive after the reaction.

3. Carbon dioxide is formed from exothermic reaction because there is release of heat energy
from the reaction when carbon is combined with oxygen to form carbon dioxide.

Points to Remember

1. A chemical change is a permanent change in which a new substance with different
properties is formed.

2. Chemical equation is the symbolic representation of a chemical reaction in terms of
symbols and formulae.

3. Chemical equation is defined as a symbolic representation of actual chemical reaction.
It represents a chemical reaction in terms of the symbol, formulae and the ratio of the
number of various reactants and products involved.

4. During the reaction the heat energy is released to the surrounding they are called exothermic
reactions.

5. During the reactions heat is absorbed from the surrounding and they are called endothermic
reactions.

Blooming Science Book 10 137

6. The main conditions required for chemical reaction are: simple contact, contact of solution,
pressure, heat, light, electricity and catalyst.

7. Chemical reaction is a process of converting one or more substances into other new substances.

8. Main four types of reactions:

a. Combination reaction b. Decomposition reaction

c. Displacement reaction and d. Acid-base reaction

9. Rate of chemical reaction is the change in the amount of the reactant or product per unit time.

10. The nature of reactants, concentration, temperature and catalyst etc. are the factors of
chemical reaction.

Project Work
Keep some steel wool or an iron nail outside your house in an open place. observe it for about
4/5 days once in a day. What change do you observe in steel wool or iron ?
What is the reddish brown layer around the wool or a nail ? Write down your observation and
draw the conclusion of this activity.

Activity for practice
Perform the following chemical reactions by yourself and also write down the balanced equations
representing them.
a. Electrolysis of water.
b. Burning of magnesium ribbon in air.
c. Placing a piece of zinc or iron in copper sulphate solution

d. Reaction between limestone and hydrochloric acid.

Exercise

1. What is a chemical reaction?

2. What do you mean by exothermic reaction? Give one example of it.

3. What are the conditions required for the chemical reaction? Explain any two with an example.

4. What is the name of reaction in which two substances exchange ions?

5. Explain the following types of chemical reactions with an example.

a. addition reaction b. single displacement reaction.

c. decomposition reaction d. double displacement reaction

6. What is acid-base reaction? Explain it with an example.

7. How do combination and decomposition reaction differ from each other?

138 Blooming Science Book 10

8. Give an example of electrolytic decomposition reaction.

9. What are the factors which influence the rate of chemical reaction?

10. Write in brief about the effect of temperature on the rate of reaction.

11. Explain the role of concentration in the rate of chemical reaction.

12. Define catalyst. Write its effect on the rate of reaction. Give two examples of negative catalyst.

13. Change the following word equations into balanced equations.

a. Hydrogen + Oxygen Water

b. Hydrogen + Chlorine Hydrogen chloride

c. Lead oxide + Carbon Carbon monoxide + Lead

d. Hydrogen + Nitrogen Ammonia

e. Potassium chlorate Potassium chloride + Oxygen

f. Aluminium + Chlorine Aluminium chloride

g. Zinc + Hydrochloric acid Zinc chloride + Hydrogen

h. Magnesium + Sulphuric acid Magnesium Sulphate + Hydrogen

i. Copper + Sulphuric acid Copper Sulphate + Water + Sulphur dioxide

j. Sodium Carbonate + Hydrochloric acid Sodium Chloride + Water +

Carbon dioxide.

k. Ammonium Chloride + Sodium nitrite Sodium chloride + Water + Nitrogen

l. Aluminium + Sulphuric acid Aluminium Sulphate + Hydrogen

m. Lime Water + Carbon dioxide Calcium carbonate + Water

n. Ammonia + Hydrogen chloride Ammonium chloride

o. Sodium carbonate + Silica Sodium silicate + Carbon dioxide

p. Sodium carbonate + Water Sodium hydroxide + Carbonic acid

q. Ammonia + Sulphuric acid Ammonium Sulphate

r. Iron + Oxygen Iron oxide

s. Aluminium + Oxygen Aluminium oxide

t. Phosphorus + Oxygen Phosphorus pentoxide

u. Ammonium chloride + Calcium hydroxide Calcium chloride + Water

15. Correct the following equations: MgNO3 + H2O
a. Mg (OH)2 + HNO3

Blooming Science Book 10 139

b. Zn + AgNO3 ZnNO3 + Ag

c. Na + H2O 2NaOH + H

d. Fe2O3 + 3HCl FeCl3 + H2O

e. Al + HCl AlCl3 + H

16. What happens when (write with balanced chemical equation):

a. Magnesium burns in air?

b. Nitrogen reacts with hydrogen in high temperature and pressure?

c. Sodium oxide is mixed with sulphuric acid?

d. Copper is treated with hydrochloric acid?

e. Pieces of potassium is placed in water?

17. Give reasons:

a. Surface area increases the rate of reaction.

b. Heat increases the rate of reaction.

23. Choose the correct alternatives from the following options.

i. The molecules combine to form a compound, what type of reaction is it?

a. Addition b. Displacement

c. Neutralization d. Decomposition

ii. NaCl and AgNO3 react with each other in ……..form.

a. Powder b. Solution

c. Molten form d. Both ‘b’ and ‘c’

iii. Glycerine is a ………catalyst

a. simple b. positive

c. reactive d. negative

iv. How is rate of chemical reaction affected by surface area of reactants?

a. Indirectly b. Directly

c. Remains same d. None of the above

v. H2 + Cl2 → 2HCl reaction occurs in presence of:

a. Darkness b. Electricity
c. Light d. Heat

140 Blooming Science Book 10

Chapter Humphey Davy

9 Acid, Base and Salt 1778AD-1825AD

Learning Outcomes Estimated Periods: 6+2

On the completion of this unit, the students will be able to:
 define acid, base and salt with examples.
 explain the general characteristics of acid, base and salt.
 differentiate between base and alkali.
 write some neutralization reactions and balance them.
 describe the uses of acid, base and salt in daily life.

We have been using various substances in our daily life. Some of these substances are different
in nature whereas some are same in their nature. We use such substances in our food, agriculture,
industries and medicines. These substances are divided into three types on the basis of their nature.
they are, acid, base and salt. For example; the acids are obtained from fruits and vegetables like
lemon(citric acid), vineger (acetic acid), chari amilo (ascorbic acid) etc, Similarly many bases
like caustic soda (sodium hydroxide) is used in preparing soap, lime (calcium oxide) is used in
agriculture etc. Common salt (sodium shloride) is our kitchen salt and copper sulphate, a salt is
used as fungicide and electrolyte.

Acid

The word acid is derived from the Latin word ‘acidus’ which means sour in taste. All the
substances that are sour in taste like citric acid, tartaric acid, lactic acid etc are the examples of
acids. But acids used in laboratories like hydrochloric acid, sulphuric acid, etc can not be tasted.

An acid is defined as a substance which produces hydrogen ions (H+) when dissolved in water.
For example, hydrochloric acid, nitric acid, sulphuric acid, acetic acid, etc.

HCl H+ + Cl- Scan for practical experiment

HNO3 H+ + NO3-

H2SO4 2H+ + SO4--

CH3COOH CH3COO- +H+

(Acetic acid)

Types of Acids visit: csp.codes/c10e11

On the basis of concentration of hydrogen ions produced during ionization, acids are of two
types; they are; strong acids and weak acids.

Acids like HCl, H2SO4 and HNO3 have high degree of ionization and produce more hydrogen

Blooming Science Book 10 141

ions after complete dissociation in aqueous solution and can conduct electricity very easily. So
these acids are strong acids. They are also called mineral acids or inorganic acids because they
are obtained from non-living sources. These acids are widely used in laboratory. They have low
pH value.

Acids like CH3COOH, HCOOH, H2CO3 etc have low degree of ionization and produce less
hydrogen ions after dissociation in aqueous solution. So these acids are called weak acids. They
have high pH value.

On the basis of their origin, acids are of two types. They are organic acids and inorganic acids.

Acids that are obtained from living organism (plants and animals) are called organic acids.
Usually organic acids undergo partial ionigation and are weak in nature. For example, Acetic
acid (CH3COOH), Formic acid, Oxalic acid, Tartaric acid, etc.

Acids that are prepared in laboratories or obtained from the minerals are called as inorganic
acids. Usually inorganic acids undergo complete ionization in aqueous solution and are strong
in nature. For example, sulphuric acid (H2SO), Nitric acid (HNO3), Hydrochloric acid (HCl),etc.
Some of the Substances showing acidic properties are given in the following table:

Common substances Name of acid Formula
Lemon juice Citric acid C6H6O7
Coca-cola Carbonic acid H3CO3
Gastric juice Hydrochloric acid
Vinegar Acetic acid HCl
Oil of Vitriol Sulphuric acid
Aqua Fortis Nitric acid C2H4O2 / CH3COOH
H2SO4
HNO3

Characteristics of Acid

1. Generally acids are sour in taste.

2. Strong acids are corrosive in nature. So, we must be careful while handling strong acids.
Strong acids can damage our clothes and can cause severe burn of skin.

3. Aqueous solution of acids conduct electricity.

4. Acids change blue litmus paper into red, phenolphthalein to colourless and methyl
orange to red.

5. Action on metals
Dilute acids react with certain metals such as zinc, magnesium etc. to produce hydrogen gas and
the corresponding salts.

Mg + H2SO4 → MgSO4 + H2
Zn + H2SO4 → ZnSO4 + H2

142 Blooming Science Book 10

6. Action on base

Acids react with bases to form salt and water only i.e. acids neutralize bases. For example,
hydrochloric acid reacts with sodium hydroxide to produce sodium chloride and water.

HCl + NaOH → NaCl + H2O

H2SO4 + CaO → CaSO4 + H2O

7. Action on carbonates and bicarbonates

Acids react with metal carbonates and bi-carbonates to produce carbon dioxide, salt and water.

2HCl + Na2CO3 → 2NaCl + H2O + CO2
2HCl + CaCO3 → CaCl2 + H2O + CO2
NaHCO3 + HNO3 → NaNO3 + H2O + CO2 ↑
Uses of acids

1. Mineral acids are used in large number of industries. Of these, sulphuric acid is the most
important. Sulphuric acid is used in industrial process such as the extraction of metals, in
the production of fertilizers, cleaning agents and as an electrolyte in car batteries. Thus,
Sulphuric acid is called king of chemicals.

2. Nitric acid is used in the preparation of dyes, drugs, explosive, plastics and fertilizers.

3. Hydrochloric acid is used for making glue and bleaching in textile industries.

4. Citric acid is the source of vitamin C.

5. Carbonic acid is used in soft drinks where as tartaric acid is used for baking powder.

6. Boric acid is used for washing wounds and eyes.

7. Acetic acid (vinegar), tartaric acid, citric acid etc are used for licing taste to food.

Bases

Bases are oxides and hydroxides of metal (electropositive radical, e.g. NH4+) which neutralize
acids to form salt and water and gives hydroxide ions when dissolve in water. CuO, Na2O, CaO,
NaOH, KOH, Ca(OH)2 are bases. The OH- ions may be present in the original compound as in
KOH, NaOH, or they may be produced when compounds such as Na2O, CaO react with water.

Na2O + H2O 2NaOH 2Na+ + 2OH-

Bases which dissolve in water are called alkalies i.e. an alkali is a soluble base.

Mercury oxide, copper oxide and ferric oxide are insoluble in water

Obviously, all alkalies are bases but all bases are not alkalies. Hydroxides of sodium, potassium
and calcium and similar metals are soluble in water and they all are therefore, alkalies.

When an alkali dissolves in water, it dissociates to give a high concentration of hydroxyl ions as negative
ions. NaOH, KOH, Ca(OH)2 are strong bases as they ionize completely in the aqueous solution to give
more hydroxyl ions. NH4OH is a weak base as it ionizes partially in the aqueous solution to give
few hydroxyl ions. The four common alkalies are sodium hydroxide, potassium hydroxide, calcium
hydroxide and ammonium hydroxide. These dissociate in an aqueous solution as follows:

Blooming Science Book 10 143

NaOH Na+ OH-
KOH K+ + OH-
Ca (OH)2
NH4OH Ca++ + 2OH-
NH4+ + OH-

Some Alkalies and their Formulae

Chemical names Common substances Formula

Caustic soda Sodium hydroxide NaOH

Caustic potash Potassium hydroxide KOH

Slaked lime Calcium hydroxide Ca (OH)2
Milk of magnesia Magnesium hydroxide Mg (OH)2
Weak and Strong Bases

If almost all the molecules of alkalis dissociate into hydroxyl ions (OH-) in aqueous solution, they
are said to be strong alkalis. They produce high concentration of hydroxyl (OH-)ions in aqueous
solution. Sodium hydroxide, calcium hydroxide, etc. are some examples of strong alkalis.

If only a few molecules of alkalis dissociate into hydroxyl ions (OH-) in the solution, they are
said to be weak alkalis. They produce low concentration of hydroxyl ions (OH-) in the solution.
Ferric hydroxide, ammonium hydroxide, etc. are some examples of weak alkalis. Zinc hydroxide
[Zn(OH)2] and copper hydroxide are other examples of weak bases.

Properties of Bases

1. Generally bases are bitter in taste and their solutions are slippery or soapy to touch.

2. The soluble bases turn red litmus into blue, methyl orange into yellow and phenolphthalein
into pink colour.

3. Action on acids
Base neutralizes an acid to form a salt and water only.
CuO + H2SO4 → CuSO4 + H2O
NaOH + HCl → NaCl + H2O

4. Action of alkalies with ammonium Salts
Alkalies react with ammonium salts on heating and liberate ammonia gas
NaOH + NH4Cl→ NaCl + H2O + NH3
Ca(OH)2 + 2NH4C1 → CaCl2 + 2H2O + 2NH3

5. Action of alkalies with some soluble salts when an alkali reacts with some soluble salts like
copper sulphate, iron chloride etc. It forms insoluable hydroxide.
For eg. CuSO4 + 2NaOH → Na2SO4+Cu(OH)2

Uses of Bases

1. Sodium hydroxide is used in the manufacture of soaps, rayon, paper, dyes and mercerizing
(i.e. giving cotton a silky appearance).

144 Blooming Science Book 10

2. Calcium hydroxide is used in the preparation of mortar, plasters and bleaching powder.
3. Magensium hydroxide and aluminium hydroxide is used to correct acidity in the stomach.
4. Caustic potash is used in preparation of soft soap.
5. Ammonium hydroxide is used for making chemical fertilizer.
6. Bases are also used as cleaners and washing powders (household cleaners contain bases).

Salt

A salt is a compound formed by the partial or complete replacement of the hydrogen atom(s) of
an acid by a metal or an electropositive radical (NH4+).

Acid + Base → Salt + Water

H2SO4 + NaOH → NaHSO4 + H2O (Partial replacement)

H2SO4 + 2NaOH → Na2SO4 + 2H2O (Complete replacement)

For example: Sodium chloride and Potassium Chloride are salts. These salts when dissolved in
water ionize as follows:-

NaCl Na+ + Cl-

KCl K+ + Cl-

They do not show the properties of acid or base.

It is clear that salt ionizes to give a positive ion other than the hydrogen ion and a negative ion
other than hydroxyl ion. All salts are made of two parts. One part comes from an acid and is thus
called acidic radical while other part comes from a base or an alkali and is therefore called basic
radical. The basic radicals are positive ions and acidic radicals are negative ions.

NaOH + HCl → NaCl + H2O

Na+ OH- + H+ Cl- → NaCl + H2O (l)
Na+ in NaCl is the basic radical and Cl- is the acidic radical. Because Na+ and Cl- are derived from
base and acid respectively.

Name and formulae of some salts produced by displacing H+ of acid by Na+

Acid Salt produced on displacing H+ of the acid

HCl Sodium Chloride (NaCl)

HNO3 Sodium nitrate (NaNO3)
H2SO4 Sodium sulphate (Na2SO4)
H2CO3 Sodium carbonate (Na2CO3)

Preparation of Salt

The general methods of the preparation of salts are:

1. Direct Combination of elements (metal and non-metal)

Salts such as iron (III) chloride, iron sulphide, copper (II) chloride etc are prepared by the
direct combination of elements, For eg.

Fe + S → FeS

Blooming Science Book 10 145

2Na + Cl2 → 2NaCl
2Mg + Cl2 → MgCl2
2. Action of acids on metal

Salts can be prepared by the action of dilute acid on metal such as zinc, iron and magnesium,
e.g.

Zn + H2SO4 → ZnSO4 + H2
Mg + 2HCl → MgCl2 + H2

3. By reaction of acid on metallic oxides

Metal oxides on reaction with acids form salts. For eg.

CuO + H2SO4 → CuSO4 + H2O

ZnO + H2SO4 → ZnSO4 + H2O

4. By the neutralization of acid and base
Salt can be prepared from the neutralization of acids and bases. For eg.
NaOH + HCl → NaCl + H2O
2NaOH + H2SO4 → Na2SO4 + 2H2O

5. By the action of an acid on metallic carbonates/bicarbonates
Metalic carbonates on reaction with acids form salts. For eg.

CaCO3 + 2HCl → CaCl2 + H2O + CO2
ZnCO3 + 2HCl → ZnCl2 + H2O + CO2
Mg(HCO3)2 + H2SO4 → MgSO4 + 2H2O+2CO2

6. Displacement of a weaker metal by a stronger metal according to their positions in the
electrochemical series, e.g.

Zn + CuSO4 → ZnSO4 + Cu
Fe + CuSO4 → FeSO4 + Cu
7. By decomposition of more complex salts. For eg.

2KClO3 → 2KCl + 3O2

Properties of Salt
1. They are electrovalent compounds. They conduct electricity in aqueous solution.
2. They have high boiling point and melting point.
3. Generally they are neutral but some are acidic or basic.
4. They are either soluble (NaCl) or insoluble (CuCO3) in water.
5. Some salts are white (Nacl) while some are coloured eg. CuSO4 (blue), FeSO4 (green).

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Salts can be acidic, neutral or basic. These salts are formed under the following conditions:

Neutral salt: Salts formed by the reaction between strong acid and strong base or weak acid and
weak base are neutral salts. e.g.

a) Strong acid & strong base:

e.g. H2SO4 + KOH → K2SO4 + H2O
b) Weak acid & weak base:

e.g. CH3COOH + NH4OH → CH3COONH4 + H2O
Acidic salt: The salt formed by the reaction of strong acid with weak base.

e.g. HNO3 + NH4OH → NH4NO3 + H2O
2HCl + Zn(OH)2 → ZnCl2 + 2H2O
Acidic salts are also formed by partial displacement of hydrogen from an acid.

e.g. H2SO4 + NaOH → NaHSO4 + H2O
Basic Salt: The salt formed by the reaction of strong base with weak acid is basic salt.

e.g. NaOH + CH3COOOH → CH3COONa + H2O

KOH + H2CO3 → K2CO3 + H2O

Some Useful Soluble Salt

Chemical Name Common Name Formula
Sodium chloride Common Salt
Sodium carbonate Washing Soda NaCl
Sodium sulphate Glauber’s Salt
Magnesium sulphate Epsom Salt Na2CO3. 10H2O
Na2SO4. 10H2O
Uses of Salt MgSO4. 7H2O

1. Sodium chloride is essential to our diet. It is used as a preservative. It is also used in the
manufacture of hydrochloric acid, sodium hydroxide and washing soda.

2. Sodium bicarbonate is used as baking powder. It is used in the treatment of acidity of
stomach.

3. Copper sulphate is used for electroplating. It is also used as a fungicide.

4. Ammonium chloride is used as a electrolyte in dry cell.

5. Sodium carbonate is used in soap factories to manufacture soap and to soften hard water.

6. Ammonium sulphate and potassium sulphate are used as chemical fertilizers.

7. Silver nitrate is used as laboratory agents.

8. Ferrous sulphate (FeSO4.7H2O) or green vitrol is used in medicine to iron deficiency in
anaemia.

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9. Zinc suphate (ZnSO4.7H2O) is used for eye treatment.
10. Gypsum salt (CaSO4.2H2O) is used in prepration of cement.

Neutralization Reaction
Neutralization reaction is a reaction reaction between an acid and alkali to form salt and water.
The acid neutralizes the effect of the base and vice-versa and hence the individual properties of
the acid and the base do not exist in products formed by neutralization reaction.

HCl + NaOH → NaCl + H2O
H2SO4 + 2KOH → K2SO4 + 2H2O

Use of Neutralization Reaction
Acids and alkalies neutralize each other in our everyday life. Some uses of the neutralization
reactions are given below.

a) To control the acidity of soil
Acidity of soil affects in the yielding of crops. Soil usually has pH between 4 and 11. Most
plants grow in near neutral soil. Certain plants such as Rhododendron and Azalea grow
well in acidic soil. Plants such as cherry, juniper, birch etc grow well in alkaline soil.
Sometimes soil is either too acidic or too basic and it is necessary to change the pH of the
soil. Soil can be made less acidic by adding lime powder (calcium oxide).

b) In digestive system
Antacids like milk of magnesia [Mg(OH)2], and aluminium hydroxide are used to control
hyper acidity, which neutraliz the conc. HCl in our stomach.

c) In treatment of nettle sting and insect bites
Bee and ant stings are acidic as they release formic acid in the skin which is controlled by
using bases like sodium bicarbonate, baking soda or soap. While wasp sting is basic which
is controlled by using mild acids like acetic acid or vineger.

Let's Learn

1. All alkalis are bases but all bases are not alkalis. This is because some bases are soluble in water
and other are insoluble in water. Water soluble bases like NaOH, KOH etc are called alkalis. But
FeO, HgO etc are insoluble bases. So, all alkalis are bases but all bases are not alkalis.

2. Sodium Hydroxide is called strong alkali because it can easily dissolve in water to form
hydroxyl ions (OH-). It produces high concentration of hydroxyl ions (OH-).

3. Acetic acid is called weak acid because of low degree of ionisation and produces less
hydrogen ion (H+) when dissolves in water.

4. Sodium bisulphate (NaHSO4) is an acidic salt because it is produced by the partial
displacement of hydrogen from sulphuric acid molecule by sodium. It is acidic is nature.

5. Acids are sour while bases are bitter in taste. It is because acid produces hydrogen ion
which stimulates our sour taste bud in our tongue while bases produces hydroxide ion

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which stimulates our bitter taste bud in our tongue.
6. Acids are proton donor. It is because acid produces hydrogen ion in aqueous solution.
7. CaSO4.2H2O (Gypsom) is a hydrated salt as it contains molecules of water.

Points to Remember

1. Acids are the compounds that give hydrogen ions (H+) in aqueous solution.
2. Acids which dissociated almost completely in aqueous solution and give a high

concentration of hydrogen ions are strong acids.
3. Acids turn blue litmus red. Similarly acids change methyl orange into red.
4. Acids react with dilute acids to release hydrogen gas.
5. Acids react with bases to form salt and water.
6. Metal oxides are bases. Water soluble bases are alkali which give hydroxyl ions (OH-) in

solution.
7. Alkalic react with ammonium salts on heating and release ammonia gas.
8. Alkalic turn red litmus blue. Similarly alkalis change methyl organce yellow and

phenolphathalein to pink.
9. In neutralization reaction, acid reacts with base to give salt and water.
10. A metal displaces hydrogen of the acid completely or partly and forms salt.
11. Salt could be neutral or acidic or alkaline.

Project Work
To find PH value of soil
1. Take about 10 gm of soil in a beaker of which the pH value is to be measured.
2. Add about 20ml distilled water to it and stir it well.
3. Filter and mixture to separate residue (soil) and clear solution (filtrate).
4. Use pH paper or pH meter or universal indicator solution to measure pH of the clear
solution.
5. From this, you will get the pH value of the sample soil. Note the obtained result with
the help of pH scale.

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Exercise

1. Define acid with examples. Write its properties and some uses.
2. What is an alkali? Name one strong alkali. Write its properties and some uses.
3. What is salt? Write the uses and properties of salt.

4. Write the equations to represent the reactions of sodium hydroxide
(i) with zinc metal
(ii) with hydrochloric acid.

5. What happens when
a) Sulphuric acid reacts with copper ?
b) Zinc reacts with dilute hydrochloric acid ?
c) Sodium oxide and hydrochloric acid react ?
d) Hydrochloric acid reacts with potassium hydroxide ?
e) Sulphuric acid reacts with sodium hydroxide ?

6. Complete and balance the following chemical equations:
a) Al + HCl → ………….. + H2
b) CaCO3 + 2HCl → ……. + H2O + ……….
c) HCl + NaOH → ……………… + H2O

7. An element burns in oxygen to form its oxide which is soluble in water. This aqueous solution
gives blue colour with red litmus. What conclusion do you draw from the given observation?

8. Explain the type of salt with examples.
9. HCl is an acid and H2O is not an acid? Explain with the example.
10. You are given three samples of colourless solutions. How will you find out which one is acid,

an alkali and a salt?
11. A compound gives hydrogen ion and chloride ion in solution state, name the compound.

What happens when this compound reacts with sodium hydroxide? Show with balanced
equation. Also name the products formed and type of the chemical reaction.

12. Write differences between:
a. Organic and inorganic acid
b. Strong and weak acid

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