Activity
To make a magnet by single touch method
Materials required: Paper pin and a bar magnet.
Method:
1. Place paper pin on the table.
2. Rub the magnet along the pin to the other end of the pin.
3. At the other end lift the magnet and again place on the first end.
4. Repeat the same process up to 50 times.
5. Now bring the paper pin near some other paperpins.
Observation : Paper pin attracts other pins towards itself.
Conclusion : Paper pin has now become a magnet. The end of the pin from which
you start to rub becomes the pole with which you rub the pin.
Double touch method
In this method a magnetised by rubbing with two
magnets.
Activity
To make a magnet by double touch method.
Materials required: A material to be magnetised, two bar magnets.
Method:
Place north and south poles of two magnets in the
middle of an iron piece and stroke the piece with
them about 50 times as shown. The magnetic material
is magnetised. The end of the iron piece at which the
magnet is left becomes the opposite pole of the magnet.
Blooming Science & Environment Book 7 101
Electrical Method
An artificial magnet can be made by passing electricity. This method is called as
electrical method.
Activity
To make a magnet by electrical method
Materials required: An iron nail, one meter
insulated wire and dry cell.
Method:
1. Wrap an insulated wire around the nail.
2. Remove the insulator from each end of the wire.
3. Connect the terminals of the wires to the terminals of a cell.
4. Bring some paper pins close to the iron nail
Observation : Iron nail attracts pins
Conclusion : When current flows through the wire around the iron nail,
it gets magnetized.
When one end of the wire is disconnected from the cell the iron nail does not
behave like magnet. Such a magnet made with the help of electricity is called an
electromagnet.
Magnetic Induction
It is a process by which a temporary magnetism is developed in a magnetic substance,
when it is placed near or in contact with magnet.
Activity
To show magnetic induction
Materials required: A bar magnet, iron piece and iron pins.
Method:
1. Keep an iron piece on a table
2. Bring a magnet and touch one end of the iron piece.
3. Put some paper pins at the end of the iron pin.
Magnet Iron piece Nails
Observation and Conclusion: Here iron piece acts like a magnet and attracts the
paper pins. The end of iron piece or in contact with a magnet develops opposite
polarity.
102 Blooming Science & Environment Book 7
Uses of Magnet
Magnets are used for various purposes, some of the common uses of magnet are as
follows:
a) A magnet is used to find the geographical direction by navigators, sailors,
travellers, etc.
b) A magnet is used to lift the heavy loads of magnetic materials.
c) It can be used to separate the magnetic materials from the garbages.
d) It is used in various electrical appliances like radio, television, electric fan, electric
bell, mirophone,loudspeaker, etc.
e) It is used in generators and in hydro-electricity project to generate electricity.
Main Points to Remember
1. A substance that attracts magnetic substances and always comes to rest in the
north and south direction when suspended freely is called magnet.
2. Properties of magnet.
a. Magnet attracts only magnetic substances.
b. Magnet has two poles north and south.
c. A freely suspended bar magnet always points to North and South direction at
rest.
d. Like poles repel and unlike poles attract.
e. Each magnet has its own magnetic field.
f. Magnetic poles always exist in pair.
3. The region upto where magnet can attract magnet and other magnetic substances
is called magnetic field.
4. The substances which are attracted by magnet are called magnetic substances and
the substances which are not attracted by magnet are called non-magnetic sub
stances.
5. The two main methods by which a magnetic substance can be converted into
magnet are stroking method and electrical method.
6. A temporary magnetism is developed in a magnetic substance when it is placed
near or in contact with magnet. This process is called magnetic induction.
7. Demagnetization is the process by which a magnet.
8. The region or space around a bar magnet where its effect can be felt is called
magnetic field.
Blooming Science & Environment Book 7 103
PRO J ECTWORK
1. Take two bars of the same Bar Magnet
dimensions - one of soft iron
Iron Steel
and the other of steel. Place
them side-by-side in contact with Iron Steel
the poles of a magnet as shown
in the figure. Induction
magnetizes both of these bars.
Dip their free ends into iron
filing. What do you find?
You will find more iron filings
adhered to the soft iron bar than
to the steel bar.
Now, remove the permanent magnet. You will find that almost all of the ad
hered iron filings fall from the soft iron bar, while hardly any iron-filings fall
from the steel bar.
Draw the conclusion of this activity.
2. i. Hold one end of a magnet
near the collection of pins.
how many pins does it pick
up?
ii. Put the cardboard next to the
end of a magnet and repeat
the same process as done in
(i). How many pins does the
magnet pick up this time?
iii. Hold a metal sheet next to the
magnet and repeat the same
process as described earlier.
How many pins does it pick
up this time?
You will observe almost no pins in the case (iii). Draw the conclusion of this
activity.
104 Blooming Science & Environment Book 7
Exercises
1. Fill in the blanks.
a. A freely suspended magnet always points to.................................. and ..........
........................ direction at rest.
b. Magnet attracts only..................................substances.
c. Like poles..................................and unlike poles...................................
d. Magnetic poles always exist in...................................
e. A magnet made by using electric current is called...................................
f. Plastic substances and paper are..................................substances.
g. A magnet has its own..................................field.
h. Magnetic poles cannot be...................................
2. Answer the following questions.
a. What is a magnet? Define natural magnet.
b. Write the properties of magnet.
c. Define magnetic field.
d. What is magnetic induction?
e. What is an electromagnet?
f. What are magnetic and non-magnetic substances?
g. What are the methods by which a magnetic substance is converted into
magnet?
h. Describe the electrical method of making magnet.
i. How is magnet made by single touch method? Explain with a diagram.
j. How would you separate brass nails from a mixture of iron and brass nail?
l. Classify the magnetic materials with examples.
Glossary
Suspend : hang
Repel : push away or go away
Property : quality, feature
Magnetize : pull, attract, convert into magnet
Desirable : wanted, needed, required
Clip : gripping or holding device
Directive property : the property of showing direction
Navigators : one who guide or steer a ship, aircraft, etc.
Scatter : sprinkle or to throw about in various places
Keepers : a magnetic piece used to avoid the demagnetization
Coincide : to have same position in space
Blooming Science & Environment Book 7 105
10Chapter Electricity
Learning Outcomes Estimated Periods-3+1
On the completion of this unit, students will be able to:
• define electeicity and sources of electricity
• define conductors and insulators
• describe open and closed circuits
• define static electricity and electrical charges
• describe series and parallel combination of cells
• know uses of electricity.
You have seen different instruments that work on electricity. Electricity can be
converted into different forms of energy with different instruments. Heat and light can
be obtained from the electricity. The use and demand of elctricity goes on increasing
day by day due to modernization and technology. No one can imagine comfortable life
without electricity.
Electricity
The source of energy which can be produced by change in number of charge or by the
flow of charges in bodies is called electricity. There are two types of electricity:
1. Static electricity 2. Curent electricity
Static Electricity
Static electricity is the electricity that does not move. The word ‘static’ means standing
still. Therefore, static electricity pertains to electrical charges that remain on materials.
Static electricity is the electricity developed by transfer of electrons through friction or
rubbing. For example.
1. A balloon rubbed with wool attracts bits of paper.
2. A plastic comb rubbed against dry hair attracts small pieces of paper.
3. When nylon vest or shirt is taken off, a cracking sound is heard. Sometimes, sparks
are often seen.
4. When a mirror is wiped with a dry piece of cloth, it becomes further dusty, The
object showing such properties are said to be electrically charged. The charges so
obtained on rubbing are called static charges.
106 Blooming Science & Environment Book 7
Electrification
An atom of an element contains electrons, protons and neutrons. The electrons have
negative charge and protons have positive charge whereas the neutron has no charge.
Since the number of electrons and protons is equal in an atom, the atom is electrically
neutral.
When an atom gains electrons from other atom it becomes negatively charged due
to the excess of electrons than the protons. Similarly, if an atom loses the electrons
it becomes positively charged due to the excess of protons than electrons. Thus, by
losing or gaining electrons, the atom is charged. The phenomenon of producing charge
in an atom or in a body is called electrification.
Activity
To observe effect of charge produced. pen
Bits of paper
Materials required
1. Plastic pen 2. Piece of paper
If you bring a piece of paper near the plastic pen it does not attract the paper piece.
Now, rub pen with your hair and bring it near the pieces of paper. It is noticed that
the plastic pen attracts the pieces of paper.
A body which gains the properties of attraction by rubbing with another body is
said to be charged or electrified. Here, pen gains the electrons from the hair and
becomes negatively charged so it attracts the positively charged pieces of paper.
Charge
The electrical property of a body is called charge. There are two types of charges:
positive charge and negative charge.
Activity
To observe attraction / repulsion properties of charges.
Material required:
1. Plastic rod 2. Glass rod 3. Stand 4. Silk thread
Method:
Rub a glass rod with silk and suspend with the help of thread. The suspended rod is
electrically isolated from the surrounding so that the charge cannot change. Now, rub
a glass rod with the silk and bring nearby to the suspended rod. The two rods repel
each other that is, each rod experiences a force directed away from other.
Blooming Science & Environment Book 7 107
Again, rub a plastic rod with fur and bring it to the suspended glass rod. The two rods
attract each other. Each rod experiences force directed towards the other rod.
From this experiment it is cleared that the charge produced in a glass rod (rubbing
with silk) is in opposite nature to the charge produced in the plastic rod (rubbed with
fur)
1. The charge like that produced in the
glass rod is called positive charge. This
charge is produced when the glass rod is rubbed
with silk; glass rod losses some negatively
charged electrons and becomes positively
charged.
2. The charge like that produced in the plastic rod
is called negative charge. This charge is produced
when a plastic rod gains some electrons from fur.
Effect of Static Electricity
Static electricity has several uses, also called applications, in the real world . One main
use in printers and photocopiers where static electric charges attract ink, or toner, to the
paper. Other uses include paint sprayers air filters and dust removal static electricity
can also caused damage.One of the most common effects of static electricity in nature
is lightning.
Lightning occurs when large amount of electrostatic energy builds up in clouds from
the energy of storms. When electrically charged regions of clouds discharge their
energy, a large flash of electricity can be seen in the sky. It releases heat, light and
sound by the flow of electrons in the sky. +ve
How is lightning formed?
It was studied by Benjamin Franklin in −ve ++++++++++
1752AD for the first time.Clouds are made +++++++++++
up of many tiny vapour droplets. In the ++++++++++++
tops of the clouds, temperature is below
freezing point and water vapour turns into − −− − − − − − − − −
ice. Now, the cloud becomes a thunder − −− − − − − − − − −
cloud. Lots of small bits of ice bump into − −− − − − − − − − −
108 Blooming Science & Environment Book 7
each other as they move around. All these collisions cause a build up of electrical
charge. Lighter, positively charged particles format the top and heavier, negatively
charged particles sink to the bottom of the cloud. The electrons from the negatively
charged clouds are transferred to the clouds with positive charge and this sudden
transfer of electrons produce intensive sparks of electricity.
Most lighting happens inside a cloud, but sometimes it
happens between the clouds the ground. A mass of positive
charge builds up on the ground attracts negative charge in
the bottom of the cloud. The grounds positive charge
concentrates around anything that sticks up- trees,
lightening conductors, even people. When the positive
charge from the ground connects with the negative charge
from the clouds and a spark of lightning strikes.
A lightning rod or lightning conductor commonly called ' Trishul'
is kept on the top of a building to protect from lightening. This
rod is connected to the ground with the help of copper wire which
is called as earthing or grounding. The copper wire transfers the
electricity generated during lightning at the top of house and
discharge into the ground without any damage to the building.
Current Electricity
Electricity is a kind of energy which is produced by the flow of charges (electrons).
It is produced by electric cell and dynamo or generator which can be converted into
different others forms of energy by using various devices. We use electricity for
lighting, heating & operating various electrical appliances and electronics.
The flow of charges per unit time is called electric current. To use electrical energy, it
needs to flow in the fixed path which is called electric circuit.
Electric Circuits
The path of flow of electricity starting from one terminal of a cell and returning to the
other terminal is called an electrical circuit. The conducting path of electricity is made
by connecting a source of electricity to an electrical appliance via conducting wires.
There is usually a switch in the circuit to turn it on and off.
Blooming Science & Environment Book 7 109
Activity Scan for practical experiment
To make an electric circuit:
Materials required: a dry cell, a torch bulb, a bulb holder
and plastic coated connecting wires.
Method:
• Cut two pieces of wire about 25cm long. visit: csp.codes/c07e16
• Remove the plastics covering of the wires at each end.
• Twisting the ends of the wires, connect one end of wire to one terminal of the
bulb-holder. Then connect the other wire to the other bulb-holder terminal.
• Place the bulb in the bulb holder.
• Now take the free ends of the wires and press them tightly against the two
terminals of the dry cell.
Observation
• You can see the bulb glows.
• The electricity flows through the wire and the tiny coiled wire inside the bulb
gets heated and glows.
• The current flows from the positive terminal to the negative terminal of the dry
cell, through the bulb.
• Now, remove the wire from one terminal of the dry cell.
• You will find that the bulb does not glow any more as the electricity does not
flow in this case.
Open and Closed Circuit switch disconnect
volt bulb
If the switch is open, the bulb does not glow, so here the meter
energy is not consumed in it. Such circuits are called open
circuits. open circuit
switch connect
If the switch is on, the bulb glows, and here the electrical cell volt bulb
energy is consumed by the bulb. This type of circuit is called meter
a closed circuit.
closed circuit
Electrical circuits are most essential because we use them with electrical appliances.
Electrical appliances are used to convert electrical energy to other useful forms of
energy; like light in an electric bulb, heat in an electric heater, sound in a radio, etc.
These electrical appliances are called electrical loads.
110 Blooming Science & Environment Book 7
When the switch is “On”, it connects the wires in the switch connect
circuit, so the circuit becomes closed, in which case
load starts working. When the switch is “Off”, the wires cell wire bulb
are not connected and the circuit becomes open, so the
electrical load does not work.
Circuit Diagram and Symbols
When drawing an electric circuit, we use certain symbols. To draw the exact picture of
the instruments is difficult and inconvenient.
The circuit symbols of some of the components are given below:
cell switch wires bulb holder
Elements Symbol
S.No.
1. A cell
2. Two cells
3. Many cells
4. An open switch
5. A closed switch
6. A bulb
7. A connecting wire
8. A voltmeter
9. An ammeter
10. A filament lamp
11. Wire
Combination of Cells
In case a single cell is unable to give a desired current or voltage, the two or more than
two cells are used together. The cells are usually combined in two ways.
They are.
Blooming Science & Environment Book 7 111
1. Series combination and
2. Parallel combination
The grouping of two or more cells together in a circuit is called combination of cells.
Of course, sometimes we may have to use a mixed grouping in which some cells
are connected in series and the rows of such cells are put parallel. What kind of an
arrangement of cells one should use depends on one’s need.
Series Combination
When positive terminal of one cell is connected to the
negative terminal of the next cell and so on, the cells
are said to be connected in series.
Such combination of cells has the following features:
a. The total voltage is equal to the sum of the voltage of the individual cells. If the
voltage of a cell is 1.5 V, then two cells combined in series has 3. 0V. It means the
voltage of the combined cells (battery) is two times more than any one cell.
V = V1 + V2 + V3
b. The current is increased with the increase in the number of cell. The brightness of
the bulb increases with the increase in the number of cell in the series combination.
The bulb glows for a short time. This type of combination is used to get more
voltage and low current.
Parallel Combination
When the positive terminals of all cells are connected
together to form one common terminal and the negative
terminals are similarly connected together to form another
common terminal, then the cells are said to be connected
in parallel.
Such combination of cells has the following features:
a. The total voltage does not increase. The total voltage is equal to the voltage of
a single cell. The voltage of the two cells in combination is equal to that of a
single cell. V = V1 = V2 = V3
b. The total current in the circuit is equal to the sum of the current through single
cells. Current in the circuit remains the same although more cells are added.
I = I1 + I2 + I3
In this type of combination, the bulb glows for a long time. The brightness of the
bulb remains the same with the increase or decrease of the cells.
112 Blooming Science & Environment Book 7
Differences between Series and Parallel Connection of cells
Series connection Parallel connection
The total voltage is equal to the sum of The total voltage is equal to the voltage
the voltage of the individual cell. due to each other.
This connection is used where large This connection is used where low voltage
voltage and low current is required. and high current is required.
The brightness of bulb is more in this The brightness of bulb is less in this
connection. connection.
The bulb does not glow for a longer The bulb glows for a longer time.
time.
Uses of Electricity
Electricity is an unavoidable helper in our life. It is used to operate appliances
like light, radio, heater, television, fan, device of communication and materials of
entertainment etc. Imagine the condition of load shedding. Some of the uses of
electricity are:
1. Light : Electricity is used to produce light, we use filament bulb and fluorescent
lamps in our house.
2. Heat: Electric kettle is used to warm up water. We use electric iron to press clothes
in our daily life. Electric heater is used to cook food and warm up the room.
These appliances contain nichrome wire inside. Nichrome wire has a high
resistance. When electric current flows through the nichrome wire, it becomes
red hot and emits heat and light. This heat is used to warm up water, cook food
and press clothes.
3. Electricity is used to run various electric devices such as TV, radio, computer,
calculator, watch, transistor etc.
4. It is also used to run electric motor, electric bell, electric vehicles etc. Electric
motors are used in pump set, trolley bus, fan etc.
5. Modern light producing appliances and instruments cannot work without
electricity.
Main Points to Remember
1. Electricity is the energy possessed by electric current.
2. The continuous conducting path through which an electric current flows is called
electric circuit.
3. An electric circuit consists of a source, conducting wires, switch load, etc.
4. There are two types of circuits they are open circuit and closed circuit.
5. An electric circuit in which current flows is called closed circuit, no current flows
is called open circuit.
Blooming Science & Environment Book 7 113
6. A standard method of drawing an electrical circuit is called circuit diagram.
7. Electricity is used
To produce light.
To produce heat.
To produce sound.
To run various electric devices like TV, radio, computer, transistor etc.
To run electric motor, electric vehicles, electric bell etc.
8. The current generated from charged particles is static electricity
9. The most significant example of static electricity in nature is lightning.
9. There are two types of combination of cells. They are series and parallel
combination.
PRO J ECTWORK
1. Open a tap so that the water comes out as a thread. Rub your comb on dry hair
andbringclosetothewatercomingfromthetap.Whathappenstoit?Oserveand
write comments.
2. Take three dry cells a bulb and some conducting wires. Connect the cells in
series and parallel turn by turn. Observe the brightness of the bulb in each
case. Draw your conclusion write down it and discuss the reason your
class.
Exercises
1. Fill in the blanks.
a. Bulb glows in..................................circuit.
b. A drawing of an electrical circuit with standard symbols is called........................
c. The substance which allows the flow of electric current is..............................
d. The device which converts electrical energy into.............................energy is
the bulb.
e. ..................................is required to run the electrical devices.
f. Two or more cells combine to form a...................................
2. Make a tick () against true and a cross (×) against false statements.
a. Plastic and paper are conductors.
b. An electric bulb converts light energy into electrical energy.
c. Aluminium and copper are the examples of conductors.
d. Electric current flows in a closed circuit.
e. Insulators are not important in electricity.
114 Blooming Science & Environment Book 7
3. Differentiate between.
a. Closed circuit and open circuit
b. Conductors and non -conductors.
c. Electric device and source of electricity.
4. Write in short.
a. Static electricity b. Conductor c. Insulator
5. Answer the following questions.
a. Name any two devices that convert electrical energy into light energy.
b. Why are the conducting wires at homes covered with plastic?
c. What is an electric circuit? Classify it.
d. Write the symbol of i) bulb ii) a battery iii) connecting wire iv) resistance
e. Why is electricity considered as our good friend?
f. List various uses of electricity in our daily life.
g. Draw an electrical circuit with an electrical cell, bulb and an off switch.
h. Draw an electrical circuit containing a cell, wire, a switch and an electric bulb
using symbols.
i. Draw a labelled diagram of dry cell.
j. What is static electricity?
k. Define series connection of cells with diagram.
l. What is lightning? How does it occur?
p. What is the use of lightning rod in a building? How does it work?
Glossary
Electric charge : the properties of some subatomic particles like protons
and electrons which causes them to exert a force on
each other.
Positive charge : Charge produced by protons.
Negative charge : Charge produced by electrons.
Cell : a device which causes the flow of charge in a circuit or
unit of life.
Local action : defect which occurs at zinc plate of simple cell due to
impurities in it.
Polarization : defect which occurs at copper plate due to formation
of hydrogen layer on it.
Blooming Science & Environment Book 7 115
11Chapter Matter
Learning Outcomes
On the completion of this unit, students will be able to: Estimated Periods: 9+2
• define matter and describe some general properties of matter.
• tell the name and symbol of some elements (Atomic number 1-20).
• define compound and make molecular formula of few compounds.
• introduce atom, molecule and molecular formula.
• define and differentiate physical and chemical change.
Introduction
We have numerous substances in our surrounding. All of them are made up of matters.
Some of these substances made by only one kind of molecules and remaining are made
up of more than one kind of molecules. Any substance around us having mass and
volume is called matter. All matters are made by molecules
Molecule is the smallest particle of substance which has the properties of a substance.
The substance which is made up of one kind of molecules are pure substance. Water
without any substances dissolved in it is a pure substance. Copper and silver are pure
metals. It is difficult to find pure substances in the nature. The smallest particle of a
pure substance is atom. It cannot be broken further into other smaller particles.
Properties of Matter
There is matter all around us. The matter may be a pure substance or an impure
substance. A substance which is made up of only one kind of molecules is called
pure substance. For example, all elements and compounds are pure substances. The
pure substances always have definite composition and properties. A substance which
is made up of two or more kinds of molecules is called impure substance. It is also
known as mixture. The mixture has no definite composition and properties.
Matter Properties of Matter
Matter occupies spaces and it has volume.
Pure substance Impure substance It has weight.
(misture) It has density.
It has its own mass.
Element Compund It changes its state on heating or cooling
116 Blooming Science & Environment Book 7
Element
An element is a pure substance that cannot be further broken down into simpler
substance even by chemical change. There are 118 elements discovered so far.
Among them 92 are found in nature while the scientists have synthesized remaining
in laboratory. The chemists are able to synthesize many different elements in the
laboratory so the number of element in the future may increase. Every element is made
up of distinct type of atoms, hence elements have different properties.
Compound
Two or more elements may chemically combine together to give new product with
different property from those of elements. Here, combination always takes place in
fixed ratio by weight. The substance thus formed is a compound. A new substance
formed by the chemical combination of two or more elements in fixed proportion by
weight is called compound.
Activity
To observe formation of compound.
Materials required
1. Test-tube 2. Burner 3. Tongs 4. Sulphur iron mixture
Method
Mix one part by weight of sulphur and two parts by weight of iron dust in a test
tube. If you bring a magnet near the mixture, the iron dust gets attracted to the
magnet leaving sulphur in the
tube. Now, remove the magnet
(alone) away and heat the test
tube strongly. Let the heated
mass be cooled and transfer the
mass in a watch glass.
Examine the mass carefully, you
can see neither the separate particle of iron and sulphur nor the mass be attracted
by a magnet. It shows that the new substance has been formed with different
property. i.e., FeS (Iron sulphide) which is a compound.
Atom
We see different types of matter around us. What actually causes difference in their
property?
The difference is because of their composition. Each matter is composed of different
building blocks called atoms. Thus, atoms are responsible for the distinctiveness of
matter from each other.
Blooming Science & Environment Book 7 117
Atom is the smallest particle of a matter, which cannot be further broken down into
simpler particle but are responsible for all the chemical changes in matter. Atoms may
or may not exist independently.
An atom is made up of three different types of particle called sub-atomic particles.
They are: Proton, Neutron and Electron.
Proton and neutron are present in the centre of an atom
called nucleus, while electrons are found outside the nucleus
revolving around it.
Proton pt =11
no =12
Proton is a stable sub-atomic particle that has a unit-positive
charge. Its mass is 1.67x10-27 kg, which is 1,837 times the Fig: Sodium atom
mass of an electron. The protons are located at the nucleus
of an atom.
Neutron
It is one of the constituent particles of every atomic nucleus except ordinary hydrogen.
It has no electrical charge and its mass is approximately equal to that of proton. They
are concentrated at the nucleus with protons.
Electron
Electron is the lightest stable sub-atomic particle. It carries a negative charge, which
is considered as the basic charge of electricity. An electron is nearly mass less. It has
a rest mass of 9.1 x 10-31 kg, which is only 0.0005 times the mass of a proton. The
electrons are orbiting around the nucleus in fixed path called orbit or shells.
Atomic Number (Z)
The number of protons present in the nucleus of the atom is called atomic number. In
a neutral atom, the number of protons is equal to the number of electrons. So, atomic
number may also be defined as the number of electrons present in an atom.
Atomic number = No. of protons = No. of electrons.
Each element has its own unique atomic number.
Atomic Mass Number (A)
The atomic mass number of an element is defined as the sum of the number of
protons and neutrons present in an atom. It is also known as atomic weight or atomic
mass number. Since the mass of an electron is extremely small, it is neglected while
calculating atomic mass.
Atomic mass = Number of neutrons + Number of protons.
A = n0 + p+
Molecule
The smallest particle of a compound or an element, that has free existence is called
molecule. Molecules may be polyatomic i.e. they may contain more than one atom,
118 Blooming Science & Environment Book 7
either similar or dissimilar. For example: hydrogen molecule contains two atoms of
hydrogen while water molecule contains two atoms of hydrogen and one oxygen atom.
Molecules are the result of chemical reaction between different substances and have
different property with respect to the reactants. e.g. Carbon dioxide.
Carbon + Oxygen Carbon dioxide
(Solid) (Gas) (Gas)
When carbon is burnt in air, carbon dioxide is produced. Here carbon is a compact
solid, while oxygen is gas that supports burning whereas carbon dioxide is a gas
different from oxygen and helps to extinguish fire rather than to support burning.
Symbol
Each element is given a specific name. These elements react with each other and form
compounds. It is difficult to represent an element in its compound with its long name.
So, the scientists have adopted a system of using short form for the full names of
elements. For example, H represents hydrogen, O represents Oxygen, Ca represents
Calcium and so on.
A symbol is defined as the short representation of an element by using one or more
alphabets. A symbol is a short and abbreviated form for the full name of an element
from their English, Latin and Greek names. Symbol of an element is mainly obtained
from the first letter of its name. It is often possible to use two or more letters as the
symbol of an element if two or more element have their names started with a common
letter. The first letter of the symbol of an element should be a capital letter whereas the
second letter is small.
Symbol of elements having atomic number 1-20 are given in the following
table.
S. No. Atomic No. Elements Symbol
1. 1 Hydrogen H
3. 2 Helium He
3. 3 Lithium Li
4. 4 Beryllium Be
5. 5 Boron B
6. 6 Carbon C
7. 7 Nitrogen N
8. 8 Oxygen O
9. 9 Fluorine F
10 10 Neon Ne
11. 11 Sodium (Natrium) Na
12. 12 Magnesium Mg
13. 13 Aluminium Al
Blooming Science & Environment Book 7 119
14. 14 Silicon Si
15. 15 Phosphorus P
16. 16 Sulphur S
17. 17 Chlorine Cl
18. 18 Argon Ar
19. 19 Potassium (Kalium) K
20. 20 Calcium Ca
The symbol of some elements are derived from their Latin names. The Latin names
and symbols of some elements are:
Element Latin Name Symbol
Copper Cuprum Cu
Lead Plumbum Pb
Iron Ferrum Fe
Sodium Natrium Na
Potassium Kalium K
Silver Argentum Ag
Mercury Hydrargyrum Hg
Gold Aurum Au
Tin Stannum Sn
Symbol is very important in chemistry. It is easier to know the element with the help
of its symbol. It takes less time and labour for writing the symbol of an element than to
write the whole name. The use of symbol is very significant for arranging the elements
in periodic table.
Symbol of some other common elements are included in the following table:
S.No. Name of element Symbol
1. Zinc Zn
2. Bromine Br
3. Iodine I
4. Chromium Cr
5. Uranium U
6. Barium Ba
7. Krypton Kr
8. Cobalt Co
9. Nickel Ni
10. Arsenic As
120 Blooming Science & Environment Book 7
Valency
The combining capacity of an element is called valency. The combining capacity
of hydrogen, oxygen and chlorine is taken as standard for valency. The valency of
hydrogen is taken as 1 and the valency of any other element is the number of hydrogen
atoms with which one atom of that element combines. Similarly the valency of chlorine
is also taken as one.
Let us study the following formulae to know the valency of an element:
S.No. Name of compound Formula Valency
Valency of O = 2
1. Water H2O Valency of N = 3
2. Ammonia NH3 Valency of C = 4
3. Methane CH4
Valency of oxygen, i.e., 2 is also taken as standard valency, if an element combines
with oxygen. The valency is twice the number of oxygen atom with which an atom of
that element combines. For example in the compound copper oxide (CuO) the valency
of the copper is 2.
The valency of elements having atomic number 1-20 is given in the following
table:
S. No. Elements Symbol Valency
1. Hydrogen H 1
2. Helium He 0
3. Lithium Li 1
4. Beryllium Be 2
5. Boron B 3
6. Carbon C 4
7. Nitrogen N 3
8. Oxygen O 2
9. Fluorine F 1
10. Neon Ne 0
11. Sodium Na 1
12. Magnesium Mg 2
13. Aluminium Al 3
14. Phosphorus P 4
15. Silicon Si 3
Blooming Science & Environment Book 7 121
16. Sulphur S 2
1
17. Chlorin Cl 0
1
18. Argon Ar 2
19. Potassium K
20. Calcium Ca
Radical
Molecule of compound is made up of two parts, each part can be an atom or a group
of atoms which has positive or negative charge. An atom or group of atoms which
behaves as a single unit in a chemical reaction is called a radical.
The radical cannot exist independently. They are found in combined state with other
atoms of elements or other radicals.
S.N. Name of radical Symbol Valency
1. Oxide O− − 2
2. Chloride Cl− 1
3. Hydroxide OH- 1
4. Sulphate SO4− − 2
5. Carbonate CO3− − 2
6. Chlorate ClO3− 1
7. Nitrate NO3− 1
8. Phosphate PO3− − − 3
9. Ammonium NH4+− 1
10. Sulphite SO3− − 2
Molecular Formula
The symbolic representation of a molecule of a substance is called molecular formula.
It represents a molecule of an element or a compound. For example, molecular formula
of hydrogen is H2 and that of water is H2O.
The molecular formula also tells the number of atoms of an element in a
molecule.
How to write the molecular formula?
In order to be able to write molecular formula you must know the symbols and valencies
of the elements and radicals. For example, let us write the molecular formula of water
by criss-cross method.
122 Blooming Science & Environment Book 7
Step I. Write down the symbols of the elements apart from each other. Then assign
their valency on their top
1 2
H O
Step II. Exchange the valencies of the atoms.
1 2
H2 O1
Step III. Write down the formula with exchanged valency.
H2O (1 is not written)
Step IV. In case the valency of an atom or radical is the multiple of other, their HCF
is removed from the molecular formula. For example, in carbon dioxide.
4 2
C O
= C2O4 = CO2
(HCF of 2 and 4 is 2 and it is removed from the molecule by taking
common).
Step V. The radicals are written in brackets while writing molecular formula. For
example, in calcium carbonate
2 2
Ca2 CO2
= Ca2(CO3)2
= CaCO3
Molecular formula of some compounds is listed in the following table:
S.N. Name of compound Molecular formula
1. Water
2. Common salt H2O
3. Carbon dioxide NaCl
4. Ammonia
5. Methane CO2
6. Hydrochloric acid NH3
7. Sulphuric acid CH4
8. Nitric acid HCl
9. Marble (Calcium Carbonate)
H2SO4
HNO3
CaCO3
Blooming Science & Environment Book 7 123
Chemical and Physical Change
When camphor is heated it changes into gas. If the molecules in gas phase are examined
by developed scientific techniques then the molecules are found to be similar to that of
solid camphor. This shows that there is not any change in molecules but simple change
in state has taken place.
straight rod bent rod
The change that occurs in the matter without losing the identity of the molecules is
called the physical change which does not produce new substances.
A change that brings about change in molecule and produces Scan for practical experiment
entirely new substances is called chemical changes.
Activity
To observe chemical charge visit: csp.codes/c07e17
Materials required
1. Test-tube 2. Burner 3. Tong 4. Sugar
Method
Take five grams of sugar in a clean and dry test tube. Heat
the test tube strongly and observe what happens there. After
some time, the white sugar changes into the black mass,
this is carbon. Taste the black mass do you feel the change
in taste. Certainly the black mass is not sweet now. Here,
the sugar undergoes the chemical change by producing the substance having
completely different properties. In fact the sugar molecules lose the identity and
become the carbon molecules.
124 Blooming Science & Environment Book 7
Differences between Chemical change and Physical change
Chemical Change Physical Change
Molecular change does not occur.
It involves the change in molecules. New substances are not produced.
It produces new substances with new It is a temporary change.
properties. Small amount of energy change occurs
during the reaction.
It is a permanent change. Melting of ice, making the hammer
from iron etc. are the examples.
Large energy change occurs during the
reaction.
Burning of wood, cooking rice, etc. are
the examples.
Differences between Element and Compound
Element Compound
An element is a pure substance
composed of only one type of atoms, A compound is composed of atoms
e.g. oxygen, hydrogen, carbon, etc. of two or more elements, e.g. water,
carbon dioxide, copper sulphate,
The number of elements is only 110. sodium chloride, etc.
An element cannot be broken into The number of compound is very large
simpler form by physical and chemical in comparison to elements.
methods.
A compound can be broken into simpler
substances by chemical methods like
electrolysis to produce elements.
Main Points to Remember
1. Any thing that occupies space and has mass is called matter.
2. A pure substance is that which is made up of only one kind of molecules.
3. An impure substance is that which is made up of two or more kinds of molecules.
4. A mixture is a substance composed of two or more elements or compounds in
any proportion by weight in such a way that each of which retains its properties.
5. An element is a substance which cannot be split up into two or more simpler
substances.
6. Symbol is the abbreviation of the name of elements.
7. A systematic arrangement of elements into groups on the basis of their similar
properties is called periodic table.
8. A physical change is a temporary change in which no new substances are formed.
Blooming Science & Environment Book 7 125
9. A physical change is a reversible change.
10. The smallest particles of matter which can exist independently is called a
molecule.
11. The smallest particle of an element which can take part in chemical reaction is
called an atom.
12. There are three sub-atomic particles in an atom. They are proton, neutron and
electron.
13. Electrons are negatively charged particles which are always revolving around
the nucleus of an atom in their orbit. They are denoted by (e-)
14. Protons are positively charged particles. They are situated at the nucleus. They
are denoted by (p+).
15. Neutrons are chargeless particles. They are located at the nucleus. They are
denoted by (n0).
16. Atomic number of an element is the number of protons or the number of electrons
present in an atom of the element.
17. Atomic mass is defined as the sum total of the number of protons and neutrons
in an atom.
18. The distribution of electrons in different orbits or shells is known as electronic
configuration.
19. A radical may be defined as a charged atom which acts as a single unit during
chemical reaction.
20. The combining capacity of elements or radicals with the other element is called
their valency.
21. Molecular formula is defined as the symbolic representation of the molecules.
PRO J ECTWORK
1. Make a chart of elements with numbers between 1 to 20 atomic
number.
2. Make some models of atoms using clay, iron rod and small balls. You can
colour them to represent proton, electron and neutron.
126 Blooming Science & Environment Book 7
Exercises
1. Fill in the blanks.
a. Atom is made up of.......................... and...................................
b. There are..................................elements in the nature.
c. Number of protons in a nucleus is called its...................................
d. Mixture formation is a..................................change.
e. Compounds are formed by..................................change.
2. State true or false and correct the false statements.
a. Element can be further broken down to new substances.
b. Molecules don’t have free existence.
c. Number of electrons is equal to number of neutron in a nucleus.
d. Number of neutron in an atom is called its atomic number.
e. Short representation of an element is called symbol.
3. Match the following item.
Column A Column B
Iron Au
Lead Be
Mercury Ag
Sodium Pb
Silicon Si
Gold Na
Phosphorous Hg
Beryllium P
4. Give the symbol of the following elements:
a. Carbon b. Neon c. Calcium d. Magnesium
h. Gold
e. Fluorine f. Hydrogen g. Oxygen
5. Define the following terms:
a. Atom b. Element c. Matter
d. Compound e. Molecule f. Symbol
g. Molecular Formula
Blooming Science & Environment Book 7 127
6. Answer the following questions.
a. What is matter? Write properties of matter.
b. Define pure and impure substances with examples.
c. What is periodic table?
d. What is symbol? Write down name and symbols of any ten elements.
e. What is meant by electron and proton?
f. Define atomic number and atomic mass .
g. What is valency? Give examples.
h. What is physical and chemical change? Explain with examples
i. What is molecular formula?
j. Define radicals with examples.
k. Distinguish between physical and chemical change.
l. What is an element? Define an atom and write sub-atomic particles.
7. Write down the difference between.
a. Atom and molecule
b. Element and Compound
c. Physical change and Chemical change
d. Symbol and Molecular formula
e. Atomic number and Atomic mass number
8. Write down the molecular formula of following compounds by criss-cross
method.
a. Water b. Methane c. Lead oxide
d. Calcium chloride e. Sodium chloride f. Potassium chlorate
g. Magnesium carbonate h. Calcium sulphate i. Sodium hydroxide
j. Sulphuric acid k. Nitric acid l. Phosphoric acid
m. Copper sulphate n. Zinc oxide o. Magnesium nitrite
p. Sodium oxide q. Aluminum chloride r. Aluminum hydroxide
s. Magnesium hydroxide t. Calcium bicarbonate u. Sulphur dioxide
128 Blooming Science & Environment Book 7
9. Name the following compounds.
a. CO2 b. MgCO3 c. ZnSO4
d. Ca(OH)2 e. (NH4)2SO4 f. NaOH
g. NaCl h. CuSO4 i. HNO3
j. (NH4)3PO4
Glossary
Gas : substance having neither definite volume nor shape.
Matter : a thing occupies space and has mass.
Element : pure form of matter made up of one type of small components.
Compound : pure substance made up of two or more elements by chemical
combination.
Molecule : tiny components present in matter that can exists independently
Atom : smallest possible unit of an element
Combustible : capable of catching fire
Compressible : that can be squeezed into a small space
Odour : smell
Transparent : something through which light passes
Blooming Science & Environment Book 7 129
12Chapter Mixture and Solution
Learning Outcomes
On the completion of this unit, students will be able to: Estimated Periods: 10+3
• define homogeneous and heterogenous mixture
• describe & deminstrate methods of seperation of mixture (evaporation,
sublimation, centrifuging and crystallization)
• describe uses of mixture
• define saturated, unsaturated and super saturated solution
• describe various uses of solution in daily life. Scan for practical experiment
A. Mixture
Mixtures are common to everyday life. We have seen rice and
sand grains mixed. Similarly, sugar solution, salt solution, tea,
coffee, etc. are examples of mixture. Thus, a mixture is formed
by the combination of two or more substances. The ratio of
the components in the mixture is never fixed. Hence, there are visit: csp.codes/c07e18
large numbers of mixtures available. When two or more than
two substances are brought together, they do not react and lie together keeping their
properties. The resulting mass formed in this way is called a mixture. In a mixture,
elements or compounds are found in combination.
There are two types of mixtures. They are:
(a) Homogeneous mixture (b) Heterogeneous mixture
Homogeneous Mixture:
In case of homogeneous mixture, the molecules of the component are intermingled
uniformly. The molecules of the component cannot be seen through the naked eye.
Such a mixture where the molecules of the mixtures are uniformly distributed is called
homogeneous mixture.
Activity
Take two glasses. Fill half of both the glasses with water. Add a little salt in one
glass and a little sugar in the other. You can see undissolved salt and sugar in the
glasses. With the help of a glass rod, stir both the glasses. Now, solution of salt
and sugar are formed in the two glasses. The salt particles and sugar particles
cannot be seen in the glass. Such a mixture (salt solution and sugar solution) is
called homogeneous mixture. Glass rod Glass rod
Salt Sugar
130 Blooming Science & Environment Book 7
Heterogeneous Mixture :
In this kind of mixture, the components can be seen through the naked eye and are not
moxed uniformly. The particle sizes of the components are different. Rice grains and
rice coats are mixed. Similarly, we can get sand particles in rice grains. These are a few
examples of heterogeneous mixture. The mixture particles can be separated by simple
mechanical or chemical means
Activity
Take three glasses. Mark the glasses ‘A’, ‘B’, and ‘C’. Put some peas (large) and
small pea grains in glass ‘A’. Put some iron filings (iron dust) and wood dust in
glass ‘B’ and put sand and water in glass ‘C’. Stir the mixtures with the help of a
glass rod. The particles of the mixture can be seen through the naked eye. Such
a mixture is called heterogeneous mixture. Here, the particle sizes of mixture are
different.
large pea iron dust water
small pea wood dust sand
A B C
Methods of Separation of Mixture
The method of separation of the components of a mixture is called separation of
mixture. The ingredients of the mixtures can be separated by using different laboratory
processes. The processes used for separating insoluble substances from a liquid
(Heterogeneous mixture) and soluble substances from a liquid (homogeneous mixture)
are different. Depending on the nature of the mixture, its volatility, melting point,
solubility, etc, different methods are adopted.
1. Centrifuging
It is a process of separating very fine suspended solid particles or semi solid from a
mixture by rotating the mixture kept in a centrifuging machine at high speed. This
method is used to separate the components of those mixtures that contain fine suspended
particles in a very little amount.
Nowadays, to separate the components of Test tube
mixture, a special instrument called centrifuging
machine or centrifuge is used. The mixture Mixture Centrifuge
is poured into test tubes of the centrifuge and
allowed to rotate at very high speed either by hand
or by electricity for a while. After sometime, the
machine is allowed to stop and then tubes are
taken out from it. Now, it is noticed that heavier
Blooming Science & Environment Book 7 131
particles are settled at the bottom of the test tubes. Finally the components of the
mixture are separated from the decantation process. This centrifuging method is used
to separate cream from milk in dairies, to separate platelets from blood in hospitals, to
separate molasses from crude sugar in sugar industries, etc.
Centrifuge is an instrument in which solid or liquid particles of different densities are
separated by rotating them in a horizontal circle around the central axis by producing
centrifugal force.
Activity
To separate chalk from the mixture by centrifuging process.
Materials required : Some chalk powder, a beaker, a
bottle, string, water
Method :
1. Take some chalk powder in a beaker and mix it with
water
2. Pour the mixture into a plastic bottle that has a tight
fitting lid.
3. Tie one end of the string around the neck of the
bottle.
4. Rotate the bottle with high speed by using the string. After sometime what will
you observe?
Observation: You will notice that the chalk has settled at the bottom while
the clear water on the top of the bottle. The clear water on top can be carefully
separated by decantation process.
2. Evaporation
This process is adopted to separate the dissolved solid particles from the solution. We
can take an example of salt solution. Here, in salt solution, salt can be separated by
using the evaporation method. The salt solution is placed in a evaporating dish. This is
placed on the top of a beaker that contains water. The water is heated slowly. The water
of evaporating dish begins to vaporize. At the end, the solid particles of salt remain left
in the evaporating dish.
Scan for practical experiment salt solution evaporating dish
burner paper wad
visit: csp.codes/c07e19 boiling water
burner
132 Blooming Science & Environment Book 7
3. Sublimation
Generally, solid melts on giving heat. But, there are also some solid substances that do
not change into liquid on heating. Instead, they change directly into gaseous state. On
condensing, the gas also directly changes into solid. Such a substance which can be
changed into gaseous state directly and condense into solid directly is called sublimate.
Camphor (naphthalene) ball, iodine, etc are examples of this type.
Activity funel
cotton(wet)
Take a mixture of sand and camphor. mixture of
The mixture is placed on an evaporating camphor and evaporating
stand. Now, put the dish on the dish
evaporating dish. Cover the evaporating sand
dish with a funnel whose stem is closed burner
with wet cotton. Now, supply gently
heat to the mixture. After sometime you Sublimation
will notice camphor being collected on
the upper surface of the funnel.
4. Crystallization
Take salt on a paper and observe it with simple hand lens. You can see all salt particles
in the same geometrical shape. This is because the crystals of salt are same. Similarly,
you can observe the particles in other substances. These are different because the
crystal of different substances have different shapes.
Thus, a crystal is a solid substance which has a regular and fixed geometrical shape
with plane faces and sharp edges.
Scan for practical experiment
crystal of salt crystal of alum crystal of copper sulphate
visit: csp.codes/c07e20
Not all the substances have the regular shape. They are found in different shapes like
glass. The particles of glass are not found in the same shape.
Thus, the solid substance which exist in the form of crystal are called crystalline solid.
Crystallization is the process of separating a pure substance in the form of crystal from
its hot saturated solution by cooling.
Blooming Science & Environment Book 7 133
Activity
To prepare the crystals of copper sulphate
Materials required: A porcelain basin, a burner or spirit lamp, a glass rod, a
tripod stand, a wire gauze, copper sulphate and water.
Method: 1. Take some amount of water in a porcelain basin and add
some copper sulphate in it.
2. tir it with the help of a glass rod to dissolve copper
sulphate.
3. Add more copper sulphate by stirring until no more of it
can be dissolved in the solution.
Place the porcelain with saturated solution over wire gauze on the tripod stand as
shown in the figure below.
Heat the solution for some time and add some more copper sulphate and stir it.
When the solution becomes thick and crystals start forming on its wall stop
heating.
Cool the porcelain basin either in air or cold water bath.
glass rod
porcelain basin
saturated solution of copper sulphate
wire gauge
tripod stand
burner
Sataurated solution Crystalization
Observation: Crystals of copper sulphate are observed after sometime. Put these
wet crystals of copper sulphate on a filter paper with the help of a glass rod. Filter
paper absorbs water present in the crystals. Now dry geometrical shaped grains of
copper sulphate crystals are formed. Observe the crystals of copper sulphate under
the microscope and write down how these crystals look.
Conclusion: Crystals of copper sulphate are formed when its saturated solution
prepared at high temperature is cooled.
134 Blooming Science & Environment Book 7
Uses of Mixture
The mixtures are used in different areas of daily life. We prepare many mixtures in
the preparation of food and beverages. In constructing houses, roads and bridges
also, different mixture are used in different ways. Some of the application and uses of
mixtures are given below.
a. Cement, sand, concrete and water is mixed for lintering (dhalan) of houses and
roofs.
b. The mixture of sand, cement and water is used in plastering walls and joining
bricks.
c. Grains of tea, water and milk is mixed to make tea.
d. Plants take different nutrients in the form of mixtures from the soil.
e. In the food and beverages, nutrients are mixed. We get energy from these nutrients
mixed in the food and beverages.
Main Points to Remember
1. A mixture is a mass formed by mixing two or more substances in any proportion
by weight so that each of which retains its own properties.
2. A homogeneous mixture is defined as a mass in which the particles of
components of the mixture are equally distributed.
3. A heterogeneous mixture is defined as a mixture in which the particles of
components are not equally distributed throughout the mixture.
4. The process by which the components of a mixture are separated from each other
is called separation of mixture.
5. All the methods of separation of mixture are based on the principle that different
materials have different properties.
6. Sedimentation and decantation, filtration, centrifuging, distillation and
sublimation, etc. are some common methods to separate the components of a
mixture.
7. The process by which impurities are separated from a mixture by rotating the
mixture in a rotating disc is called centrifuging.
8. The process of separating the insoluble solid from a liquid by passing the mixture
through filter paper is known as filtration.
9. The process of converting a solid directly into its vapour on heating is called
sublimation.
10. Sublimation is used to separate volatile components from mixture.
11. Crystal has a regular and a fixed geometrical shape.
12. Crystallization is the process of separating the solid from the solution in the form
of the crystal.
Blooming Science & Environment Book 7 135
PRO J ECTWORK
Take about 5 gm of alum and dissolve it into water. Then take the solution in a
beaker and place on a table without disturbance. How does the amount of the water
decrease in the beaker. Observe it daily and note in your copy.
Exercises
1. Fill in the blanks.
a. The mixture of salt and ...................can be separated by sublimation process.
b. Common salt is obtained from sea water by applying ........................ process.
c. The conversion of ice into water is occurred by .................................
d. Centrifuging is the process of separating................................mixture.
2. Define the following methods of separation of mixture with example.
a. Sedimentation b. Crystallization
3. Name the methods of separation which are used to separate the following
mixture.
a. Salt solution b. sand and water mixture
c. mixture of iodine and sand d. butter from milk
4. Answer the following questions in brief.
a. What is a mixture? Classify it.
b. What do you mean by the components of a mixture?
c. What is a homogeneous mixture? Give any two examples.
d. What is sediment? Define decantation.
e. Name any two mixtures which can be separated from sedimentation process.
f. What is sublimation? Name any two mixtures which can be separated from
sublimation process.
g. Write the uses of mixtures.
h. Define centrifuging.
i. What is crystallization?
j. List the methods of seperation of heterogeneous mixture.
136 Blooming Science & Environment Book 7
5. Write the differences between.
Homogeneous and heterogeneous mixture.
6. Naphthalene balls are used in a box having clothes to protect clothes from
insects.After a few days, the size of the balls gradually decreases and ultimately
they disappear. How does it occur? Explain it with reasons.
7. Explain with the help of neat and labeled diagram.
a. The process by which salt and sand are separated from the water and sand
mixture.
b. The process by which salt and water are separated from the salt solution.
c. The process by which salt and camphor are separated from the salt camphor
mixture.
8. Write any one example of each for centrifuging and filtration process which is
used in your house.
9. Rewrite the following statements with necessary corrections.
a. When a solid matter becomes vapour after heated, this is an example of
evaporation.
b. When wet clothes are dried in the sun, it is an example of sublimation.
c. Iron dust particles and iodine mixture can be separated by distillation
method.
d. When the vapour of boiled milk is cooled, it becomes milk.
Glossary
Residue : a small amount of something that remains at the end of a
process
Sediments : the solid materials that settle at the bottom of a liquid
Miscible : (of liquids) that can be mixed together
Mixture : combining of two or more substances
Evaporation : the process of changing liquid to gas by heating
Distillation : process of changing a liquid to vapour and cooling the vapour
to get back the liquid.
Homogeneous : having same composition throughout
Heterogeneous : having different composition of different parts
Blooming Science & Environment Book 7 137
B. Solution
Introduction
We use different types of mixtures in our daily life. In some mixtures we can see
the components of mixture while in some mixtures we cannot see the components of
that mixtures. A mixture can be homogeneous or heterogeneous. A mixture in which
we cannot see the constituents is called a homogeneous mixture. A mixture in which
components can be seen is called a heterogeneous mixture. A mixture of sand and
rice, maize and peas, etc are the examples of heterogeneous mixtures. A solution is a
homogeneous mixture of solute and solvent.
Solution:
Solution is a homogeneous mixture of two or more substances in which one
substance is dissolved in the other. A solution is formed when a solute and solvent are
mixed.
Solution = solute + solvent
Sugar solution = sugar + water
The substance that is dissolved in another substance sugar dissolved
is called a solute. The substance that dissolves in water
solute in it is called a solvent. In sugar solution,
sugar is a solute and water is a solvent. Similarly,
in salt solution, salt is solute and water is solvent.
In general, the amount of solute is less than the
amount of solvent in a solution.
Unsaturated Saturated and Super Saturated Solution
Unsaturated Solution
Take some water in a beaker at room temperature. Put a spoonful of common salt into
the beaker and stir it with a glass rod. The salt will dissolve. Add one more spoonful
of salt which will dissolve again at that temperature. Therefore, the solution that can
dissolve an excess of solute at a given temperature is called an unsaturated solution.
Fig A shows the presence of unsaturated solution in a beaker.
Saturated Solution
Take a beaker containing some water at a particular temperature. Add some salt in it
and stir it with a glass rod. The salt will dissolve. Repeat the process of adding more
and more salt in the given amount of water. Finally at a point, no more salt dissolves
in that solution at a particular temperature. This means that a given volume of water
can dissolve the limited amount of solute at a particular temperature. Therefore, the
solution which cannot dissolve excess of solute at a particular temperature is called a
saturated solution. Fig B shows the presence of saturated solution in a beaker.
138 Blooming Science & Environment Book 7
glass rod glass rod glass rod
salt crystal salt crystal salt crystal
beaker C
AB
Differences between Unsaturated and Saturated Solutions
Unsaturated Solution Saturated Solution
It is a solution that can dissolve excess It is a solution that cannot dissolve any
of the solute at a particular temperature. more solute at a particular temperature.
On heating, it becomes more unsaturated. On heating, it becomes unsaturated.
It is less dense than the saturated It is denser than the unsaturated
solution. solution.
Supersaturated Solution
Take a beaker, half of which is filled with a saturated solution and heat it. On heating,
the solution no longer remains saturated because the solution becomes unsaturated and
dissolves more solute when you heat. On cooling, such solution withdraws the excess
of solute. Such solution is called supersaturated solution. Fig C is an example of super
saturated solution.
Therefore, a solution in which excess solute is dissolved than required amount to make
a saturated solution at a given temperature is called supersaturated solution.
Activity
To test whether the solution is unsaturated, saturated and super saturated solution.
Materials required : beakers, a glass rod, salt crystals, salt solution of different
concentrations.
Method :
glass rod glass rod salt crystal
salt crystal salt crystal
beaker BC
A Blooming Science & Environment Book 7 139
1. Take beakers A, B and C and fill with equal amount of salt solution of different
concentrations.
2. Put calculated amount of salt in each beaker.
3. Stir the solution of each beakers with a glass rod. What will you see in each
beaker containing the salt solution.
Observation
In the beaker A, the crystals of salt are completely dissolved. In beaker B, there is
no change in the amount of the crystal of salt when put. In the beaker C, there is
increase in the size of the crystal of salt in the solution.
Conclusion
This activity confirms that the solution of the beaker A is unsaturated solution. The
solution of the beaker B is saturated solution and the solution of the beaker C is
the supersaturated solution
Differences between Unsaturated, Saturated and Supersaturated Solution
S. Unsaturated Solutio S. Saturated Solution S. Super Saturated
N. N. N. Solution
1. It can dissolve more 1. It cannot dissolve 1. It cannot dissolve any
solute. more solute more solute.
at a particular
temperature.
2. Temperature does not 2. Temperature affects 2. By increasingly the
affect it. it. temperature more
solute may dissolve.
On cooling or decrease
in temperature, they
appear as crystals.
3. It has more solvent 3. It has more solute 3. It has maximum
and less solute. dissolved than in amount of solute.
unsaturated solution.
Concentrated and Dilute Solutions
For a given solution, the amount of the solute dissolved in a unit amount of the solvent
is called the concentration of the solution.
Concentrated Solution: The solution that has relatively large amount of solute for a
given solvent is called the concentrated solution.
Dilute Solution: The solution that has relatively less amount of the solute for a given
solvent is called the dilute solution.
140 Blooming Science & Environment Book 7
The terms dilute and concentrated are relative. The same solution may be dilute
relative to one solution but concentrated relative to another solution.
Activity
Copper
sulphate
solution
A BC
Take three beakers A, B and C filled with equal amount (say 500 ml) of water.
Put one teaspoonful of coper sulphate in the beaker A, two teaspoonful of coper
sulphate in the beaker B, and three teaspoonful of coper sulphate in the beaker
C. Stir them with a glass rod. The solution in the beaker B is more concentrated
than the solution in the beakerA. But it is less concentrated than the solution in
the beaker C. The solution in the beaker B is concentrated in comparison to the
solution in the beaker A but it is dilute in comparison to the solution in the beaker
C. So the concentration of solution is a relative term.
Importance of Solution
The following are the importance of solution:
1. Oxygen is found dissolved in water and in air that is used by living organisms for
respiration.
2. Plants take the different minerals and salts from the soil in the form of solution.
3. The digested food particles reach the different parts of the body in the form of
solution.
4. Most of the reactions are taking place easily in the form of solution.
5. Most of the medicines and paints are found in the form of solution.
6. Solution is essential in many industries.
Main Points to Remember
1. Solution is a homogeneous mixture of two or more than two substances either
solid and liquid or liquid and liquid or liquid and gas.
2. A substance which has a capacity of dissolving another substance is known as
solvent.
3. A substance which get dissolved into another substance is called solute.
4. A solution in which more quantity of solute can be dissolved without increasing
the temperature is unsaturated solution.
Blooming Science & Environment Book 7 141
5. A solution in which no more of solute can be dissolved by increasing the
temperature is saturated solution.
6. A solution which tends to throw out excess solute when the temperature is
lowered is called super saturated solution.
7. Saturated solution is mostly affected by change in temperature.
8. Solution is very important for the growth of living things.
PRO J ECTWORK
1. From a solution of sodium chloride (salt) & prepare its crystals.
2. Prepare a solution of copper sulphate and separate crystals from it.
3. Prepare dilute and concentrated solution of sugar. Taste them and write their
properties.
Exercises
1. Fill in the blanks.
a. ................................ is the mixture of solute and solvent.
b. A solid that gets dissolved itself in the solvent is called ................................
c. ................................ make the solute dissolve in it.
d. ................................ is a solution with less solute.
e. Solution is important for ................................ of plant.
2. State whether the following statements are true or false.
a. A mixture of rice and wheat grains is homogeneous mixture.
b. Unsaturated solution can dissolve more solute at a given temperature.
c. In concentrated solution, solute is more.
d. We need food in the form of solution.
e. Supersaturated solution contain undissolved solute substance in the solution.
3. Answer the following questions.
a. What is saturated solution?
b. What is dilute solution? Define concentrated solution.
142 Blooming Science & Environment Book 7
c. What is supersaturated solution?
d. Why are solution important?
e. What is meant by solution?
f. What are the components of the solution?
g. If you are given a solution, how would you know whether the given solution
is saturated, unsaturated or supersaturated? Explain.
h. What is meant by unsaturated solution?
i. Describe how do you prepare a saturated solution of copper sulphate and get
crystal from it.
j. What effect will be there in saturated solution with change in temperature?
4. Name six solutions with their constituent solvent and solute in the following
table. One is done for you.
S. No. Solution Solvent Solute
1. Salt solution Water Salt
2.
3.
4.
5.
6.
Glossary
Crystal : homogenous solid substance having geometrical shape.
Crystallization : the process of obtaining crystal
Chromatography : the process of separating of different colours
Centrifuge : a machine used for centrifuging process.
Saturated solution : when no more solute dissolve in a solution at a certain
temperature
Constituent : component, part of solution
Blooming Science & Environment Book 7 143
13Chapter Metals and Non-metals
Learning Outcomes
On the completion of this unit, students will be able to: Estimated Periods: 4+1
• explain the properties of metals and non-metals and to distinguish them.
• explain the properties of alloys.describe alloys
• describe the general properties and uses of some substances like sulphur,
iodine, brass and bronze.
Introduction
At present 118 elements are known. On the basis of certain important properties,
these elements are divided into two classes: metals and non-metals. A large number of
elements (about 80%) are metals.
Copper was the first metal to be used by human beings. They have been using different
kinds of metals for different purposes. Metals are so vital to us that it is unthinkable
to live without them. They are essential for the construction of houses, transportation,
communication, electricity, household articles, scientific instruments, weapons,
automobile parts, coins, etc.
Metals like gold and silver are rust free. They are used in making valuable ornaments.
Most of the metals do not exist in the native form, with the exception of few like gold
and platinum.
Metals
Since ancient time, humans are using metals. Metals are used in making cooking
utensils for the kitchen and in making different electrical appliances also. Metals
are generally hard, shiny and good conductors of heat and electricity. Mostly they
are found in solid state. Iron, copper, gold, silver, aluminium etc are the examples of
metals. Important general properties of metals are given below:
a) Generally metals are found in solid state.
b) Metals are hard in nature.
c) Metals are good conductor of heat and electricity.
d) Metals possess metallic lustre i.e. they are shiny in nature.
e) Metals can be beaten into thin sheet, the property is called malleability. They can
also be changed in the form of wire, which is called as ductility. So, the metals are
usually malleable and ductile in nature.
f) Metals produce sonorous sound on hammering.
g) Generally the metals have high melting and boiling points.
144 Blooming Science & Environment Book 7
Non-Metals
Among 118 elements existing in nature about 20% are non-metals. Non- metals are soft
in nature and found in all three states. These are bad conductor of heat and electricity.
The non-metals possess some general properties which are listed below:
a) Metals are found in all three states like solid, liquid and gas.
b) They are soft in nature.
c) They are non-malleable and non-ductile.
d) They do not produce sonorous sound and do not possess lusterous property.
e) They are bad conductors of heat and electricity.
f) Non-metals are brittle in nature which can be broken down easily into pieces.
Carbons, oxygen, nitrogen, sulphur, etc are some examples of non- metals.
Differences between Metals and Non-metals
Properties Metals Non-metals
State All the metals except mercury, Non-metals are found in all three
are solid at the ordinary states.
temperature.
Lustre Metals possess metallic lustre Non-metals, except iodine and
when freshly cut. graphite, do not possess any
metallic lustre.
Hardness They, except sodium are They, except diamond, are
generally hard because the generally soft in nature. Diamond
molecules are closely packed in is known as the hardest substance.
them.
Breakability Metals are hardly broken into They are easily broken.
pieces.
Melting and The melting and boiling point The melting and boiling point are
boiling point are generally high. generally low.
Clink sound Metals, when struck with a Non-metals do not emit any
Malleability hammer, emit a peculiar sound metallic sound.
which is called metallic clink
sound.
Metals can be beaten into a thin Non-metals are non-malleable.
plate. Such property is called
malleability. So metals are
malleable.
Blooming Science & Environment Book 7 145
Ductility Wire can be made from metals. Non-metals are non-ductile.
Such property of metals is
called ductility. So metals are Non-metals, except graphite
ductile. generally do not conduct heat and
electricity.
Conductivity Metals are generally good Non-metals generally do not form
alloys.
conductors of heat and
electricity.
Alloy Metals have the power of
formation dissolving other metals to form
homogeneous mixture. This
mixture is called alloy.
Metalloids
There are certain elements which have some properties that are typical of metals as well
as some properties that are typical of non-metals. Such elements are called metalloids.
Metalloids possess the following characteristics.
1. They are poor conductor of heat and electricity.
2. They possess metallic luster.
3. They are neither malleable nor ductile.
4. They form alloys.
For example, antimony (Sb) has a metallic appearance but it is brittle like non-
metals. Metalloids form the dividing line between metals and non-metals. Boron (B),
silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb) and Tellurium (Te) are
metalloids.
Alloys
Alloys can be made by mixing two or more than two metal (s) and non-metal (s) or
metals in liquid state. After cooling the mixture, the solid mass is formed. The solid
mass is called alloy. Thus, an alloy is defined as a homogeneous mixture of two or
more metals and non-metals. Brass, steel and stainless steel, etc. are the examples of
alloys. The composition, properties and uses of some common alloys are given in the
following table:
Name of alloy Composition Use Properties
can be easily moulded,
Brass copper & zinc cartridge cases, resists corrosion
musical instruments,
Bronze copper & tin machine parts hard, can be easily asted
statues, coins, edals
146 Blooming Science & Environment Book 7
Steel iron & carbon utensil resists corrosion
Stainless steel iron & carbon cutlery and machine resists corrosion
nickel, parts
chromium
Properties of alloys
1. Alloys are generally harder than their components.
2. Alloys increase the strength of metals, e.g., the strength of iron can be increased
by alloying it with nickel.
3. They are good conductor of heat and electricity.
4. They are malleable and ductile.
5. Generally they are brittle in nature.
Some Useful Non-metals and Alloys
Sulphur
Symbol : S
Atomic number : 16
Atomic mass or weight = 32
Melting point = 115.21oC
Boiling point = 444.6oC
Elemental sulphur is a bright yellow crystalline solid at room temperature. Chemically,
sulphur can react as either an oxidant or reducing agent. It oxidises most metals and
several non-metals including carbon.
In nature sulphur can be found as the pure element and as sulphide and sulphate
minerals. In Bible sulphur is referenced as brimstone meaning burning stone. In 1777,
Antoine Lavoisier convinced the scientific community that sulphur was a basic element
rather than a compound.
Uses:
1. Sulphur can be used to increase the resilience and toughness of rubber.
2. As an insecticide: Sulphur forms lime sulphur spray on heating with lime
which is used as an insecticide.
3. It is used to manufacture sulphuric acid.
4. It is used to make sulpha-drugs which are used to treat skin diseases.
5. For the manufacture of black gunpowder, sulphur is used. It is high quality
gunpowder.
6. Sulphides of phosphorous and antimony are used in the production of safety
matches.
Blooming Science & Environment Book 7 147
Iodine
Iodine was discovered by Bernard Courtosis in 1811. Iodine is the chemical element
with symbol I and atomic number 53. The name is from the Greek word ‘iodes’meaning
violet or purple, due to the colour of elemental iodine vapour.
Symbol : I
Atomic number : 53
Atomic mass : 127
Melting point : 113.7oC
Boiling point : 184.3oC
Iodine and its compounds are primarily used in nutrition and industrially in the
production of acetic acid and certain polymers. Iodine is mainly found in earth as the
highly water soluble iodine I−, which concentrates in oceans and brine pools.
Iodine is required by higher animals, which use it to synthesize thyroid hormones.
Because of this function, radioisotopes of iodine are concentrated in thyroid gland
along with non-radioactive iodine.
Uses of Iodine:
Iodine is used:
(i) In medicines, e.g. for the preparations of tincture of iodine (solution of iodine
in alcohol and water containing potassium iodide), and iodex (iodine dissolved in
petroleum jelly).
(ii) For preventing goiter. For this purpose 0.023% NaI and KI are added to the
table salt to make up for the deficiency of iodine. Such a salt is called iodized
salt.
(iii) For the manufacture of organic compounds, like dyes, drugs, iodoform (CHI3)
etc. and in photography.
(iv) Iodine solution is also used as an oxidizing agent for qualitative and volumetric
analsis.
(v) It is also commonly used in brachytheraphy implanted capsules, which kill
tumors by local short range gamma radiations.
Brass
Brass is an alloy of copper and zinc. The proportions of zinc and copper can be varied
to create a range of brasses with varying properties. It is used for decoration because
of its gold like appearance and for applications where low friction is required such
as locks, gears, bearings, doorknobs, ammunitions and valves, for plumbing and
electrical applications and extensively in musical instruments such as horns and bells
for its acoustic properties.
148 Blooming Science & Environment Book 7
It is also used in zippers. Because it is softer than most other metals
in general use. Brass is often used in situation where it is important
that sparks not be struck as in fittings and tools around explosive
gases.
Brass has muted yellow colour which is somewhat similar to gold. It is relatively
resistant to tarnishing, and is often used as decoration and for coins. In antiquity,
polished brass was often used as a mirror.
Properties
The malleability and acoustic properties of brass have made it the metal of choice for
brass musical instruments such as the trombone, tuba, trumpet etc.
Brass has higher malleability than bronze or zinc. The relatively low melting point of
brass (900 to 940oC) and its flow characteristics make it a relatively easy material to
cast.
By varying the proportions of copper and zinc properties of brass can be changed,
allowing hard and soft brasses.
Uses
1. Brass is used to make some household utensils like water vessel etc.
2. It is used for making locks, gears, bearings doorknobs etc.
3. It is used in brass musical instruments such as horns and bells.
4. It is used in plumbling as fiftings.
Bronze
Bronze is metal alloy consisting primarily of
copper, usually with tin as the main additive. It is
hard and brittle and it was particularly significant
in antiquity. So much so that the Bronze Age was
named after the metal. However, since "bronze" is a somewhat imprecise term and
historical pieces have variable compositions in particular with an unclear boundary
with brass.
Properties
Bronze is considerably less brittle than iron. Typically bronze oxidizes superficially;
once a copper oxide layer is formed, the underlying metal is protected from further
corrosion. However, if copper chlorides are formed a corrosion mode called “bronze
disease” will eventually completely destroy it. Copper based alloys have lower melting
points than steel or iron and are more readily produced from their constituent metals.
They are generally about 10% heavier than steel. Bronze resists corrosion and metal
Blooming Science & Environment Book 7 149
fatigue more than steel and is also a better conductor of heat and electricity than most
steels.
The melting point of bronze varies depending on the actual ratio of the alloy components
and is about 950oC. Bronze is non-magnetic.
Uses
1) It was suitable for boat and ship fitting before the invention of stainless steel. It
is still used in ship propellers and submerged bearings.
2) It is used in guitar and piano strings.
3) Bronze struck against hard surface will not generate sparks so it is used to
make hammers, mallets, wrenches and other durable tools to be used in explosive
atmospheres.
4) Bronze is used to make bronze wool for wood working applications where steel
wool would discolour.
5) In Hindu artisans bronze is oak used to create intricate statues.
6) It is used in bells, cymbals etc.
8) Bronze is used to make medals being awarded to second-runner up in sporting
competitions.
Main Points to Remember
1. There are 118 elements known. They are classified into metals and non-metals.
2. Metals are hard, malleable, dutile and shiny.
3. Non-metals are soft except diamond and are bad conductor of heat and electricity
execpt graphite.
4. Substances which have properties of both metals and non-metals like antimony,
silicon, germination etc are called metalloids.
5. Sulphur is a non-metal with atomic number 16 and it is used in bio-chemical
process.
6. Iodine is an element with atomic number 53 and atomic weight 126.9.
7. A substance which is formed from two or more metals is an alloy. Brass is an
alloy of copper and zinc and bronze is an alloy of tin and copper.
150 Blooming Science & Environment Book 7
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