NCERT Textbook: Particulate Nature of Matter | Science Curiosity Class 8 - New NCERT PDF Download

 Page 1


98
Curiosity — Textbook of Science for Grade 8
Particulate Nature 
of Matter 
7
 
 z Why is it possible to pile up stones or sand, but not a liquid like 
water?
 z Why does water take the shape of folded hands but lose that 
shape when released?
 z We cannot see air, so how does it add weight to an inflated 
balloon?
 z Is the air we breathe today the same that 
existed thousands of years ago?
 z Share your questions 
  ?
Probe and ponder
Chapter 7.indd   98 Chapter 7.indd   98 6/28/2025   2:52:43 PM 6/28/2025   2:52:43 PM
Page 2


98
Curiosity — Textbook of Science for Grade 8
Particulate Nature 
of Matter 
7
 
 z Why is it possible to pile up stones or sand, but not a liquid like 
water?
 z Why does water take the shape of folded hands but lose that 
shape when released?
 z We cannot see air, so how does it add weight to an inflated 
balloon?
 z Is the air we breathe today the same that 
existed thousands of years ago?
 z Share your questions 
  ?
Probe and ponder
Chapter 7.indd   98 Chapter 7.indd   98 6/28/2025   2:52:43 PM 6/28/2025   2:52:43 PM
Chapter 7?—?Particulate Nature of Matter
99
You might have collected pebbles and stones from the sand while 
playing on a riverbank or a beach. Where do these pebbles, 
stones, and sand come from? 
In the mountains, rocks gradually break down due to erosion. 
Rivers flowing through these regions carry along the eroded rock 
pieces. As the rivers flow, they continue to break down the rocks 
further into pebbles, stones, sand; and transport large quantities 
of them to the plains.
The bigger rocks are eventually broken down into finer grains 
of sand and clay. Is this grain the smallest unit of a bigger rock 
or can these grains of sand and clay be broken down further? 
Let us find out!
7.1 What Is Matter Composed of?
    Activity 7.1: Let us explore
 z Take a stick of chalk (Fig. 7.1a) and break it into two 
pieces (Fig. 7.1b). 
 z Continue breaking the chalk till it becomes difficult 
to break it further by hand.
 z Grind the small pieces of chalk thus obtained 
(Fig. 7.1c) using mortar and pestle.
 z Observe the fine powder of chalk with a magnifying 
glass (Fig. 7.1d).
 z What do you observe?
 z Each tiny grain you observe is still a speck of chalk.               
Is every speck of this fine 
chalk powder still composed 
of the same substance, 
or has it changed into 
something else on breaking 
or grinding?
Recall Curiosity, Grade 7 chapter ‘Changes Around 
Us: Physical and Chemical’— is grinding chalk a physical 
change or a chemical change? You learnt that the chalk 
does not change into a new substance on grinding. It is a 
physical change in which only the size of each speck of 
chalk has reduced further.
(a)
(b)
(c) 
(d)
Fig. 7.1: (a) A stick of 
chalk; (b) The chalk stick 
broken into two pieces; 
(c) A piece of chalk 
ground into fine powder; 
(d) A close-up view of 
chalk powder under a 
magnifying glass 
Chapter 7.indd   99 Chapter 7.indd   99 6/28/2025   2:52:45 PM 6/28/2025   2:52:45 PM
Page 3


98
Curiosity — Textbook of Science for Grade 8
Particulate Nature 
of Matter 
7
 
 z Why is it possible to pile up stones or sand, but not a liquid like 
water?
 z Why does water take the shape of folded hands but lose that 
shape when released?
 z We cannot see air, so how does it add weight to an inflated 
balloon?
 z Is the air we breathe today the same that 
existed thousands of years ago?
 z Share your questions 
  ?
Probe and ponder
Chapter 7.indd   98 Chapter 7.indd   98 6/28/2025   2:52:43 PM 6/28/2025   2:52:43 PM
Chapter 7?—?Particulate Nature of Matter
99
You might have collected pebbles and stones from the sand while 
playing on a riverbank or a beach. Where do these pebbles, 
stones, and sand come from? 
In the mountains, rocks gradually break down due to erosion. 
Rivers flowing through these regions carry along the eroded rock 
pieces. As the rivers flow, they continue to break down the rocks 
further into pebbles, stones, sand; and transport large quantities 
of them to the plains.
The bigger rocks are eventually broken down into finer grains 
of sand and clay. Is this grain the smallest unit of a bigger rock 
or can these grains of sand and clay be broken down further? 
Let us find out!
7.1 What Is Matter Composed of?
    Activity 7.1: Let us explore
 z Take a stick of chalk (Fig. 7.1a) and break it into two 
pieces (Fig. 7.1b). 
 z Continue breaking the chalk till it becomes difficult 
to break it further by hand.
 z Grind the small pieces of chalk thus obtained 
(Fig. 7.1c) using mortar and pestle.
 z Observe the fine powder of chalk with a magnifying 
glass (Fig. 7.1d).
 z What do you observe?
 z Each tiny grain you observe is still a speck of chalk.               
Is every speck of this fine 
chalk powder still composed 
of the same substance, 
or has it changed into 
something else on breaking 
or grinding?
Recall Curiosity, Grade 7 chapter ‘Changes Around 
Us: Physical and Chemical’— is grinding chalk a physical 
change or a chemical change? You learnt that the chalk 
does not change into a new substance on grinding. It is a 
physical change in which only the size of each speck of 
chalk has reduced further.
(a)
(b)
(c) 
(d)
Fig. 7.1: (a) A stick of 
chalk; (b) The chalk stick 
broken into two pieces; 
(c) A piece of chalk 
ground into fine powder; 
(d) A close-up view of 
chalk powder under a 
magnifying glass 
Chapter 7.indd   99 Chapter 7.indd   99 6/28/2025   2:52:45 PM 6/28/2025   2:52:45 PM
100
Curiosity — Textbook of Science for Grade 8
These specks of chalk powder can be broken further into 
smaller particles by further grinding. Let us imagine that this 
process of grinding continues. Eventually, we would reach a stage 
where the chalk particles cannot be broken down any further. 
The tiny units obtained at this stage 
are the basic building blocks that the 
chalk was made up of. 
This means that one whole piece of 
chalk was made up of a large number 
of smaller units. These units are called 
constituent particles of chalk. A constituent particle is the basic 
unit that makes up a larger piece of a substance or material. Just 
like chalk, the grains of sand and clay are not the smallest units 
of bigger rocks. These are also made up of a large number of 
their constituent particles.
Let us explore further!
Recall the dissolution of sugar into water to form a solution. 
What happens to sugar when it is dissolved in water?
Activity 7.2: Let us perform
 z Fill a glass tumbler with 
drinking water. 
 z Put two teaspoons of sugar 
into it.
 z Do not stir the water. Taste a 
small spoonful of water from 
the top layer of the glass.
Does the water taste sweet? 
 z Now, stir the water until the sugar dissolves completely 
(Fig. 7.2). 
 z Again taste a spoonful of water from the top layer.
What difference in taste do you notice? Does it taste sweet? 
Since the top layer of water tastes sweet after dissolving 
sugar, it must be present in the solution. Do you observe any 
sugar particles in the solution? 
Sugar particles can no longer be observed but their 
presence can be sensed by taste. When sugar dissolves in 
water, it breaks up into its constituent particles which cannot 
be broken down further. Each tiny grain of sugar is made up 
of millions and millions of such constituent particles.
Are the units of chalk 
obtained in this manner 
considered the smallest 
units of chalk?
Fig. 7.2: Dissolving 
sugar in water
Safety first
Perform the activity under the 
supervision of a teacher or an adult. 
Never eat or drink anything unless 
asked to.
Chapter 7.indd   100 Chapter 7.indd   100 6/28/2025   2:52:49 PM 6/28/2025   2:52:49 PM
Page 4


98
Curiosity — Textbook of Science for Grade 8
Particulate Nature 
of Matter 
7
 
 z Why is it possible to pile up stones or sand, but not a liquid like 
water?
 z Why does water take the shape of folded hands but lose that 
shape when released?
 z We cannot see air, so how does it add weight to an inflated 
balloon?
 z Is the air we breathe today the same that 
existed thousands of years ago?
 z Share your questions 
  ?
Probe and ponder
Chapter 7.indd   98 Chapter 7.indd   98 6/28/2025   2:52:43 PM 6/28/2025   2:52:43 PM
Chapter 7?—?Particulate Nature of Matter
99
You might have collected pebbles and stones from the sand while 
playing on a riverbank or a beach. Where do these pebbles, 
stones, and sand come from? 
In the mountains, rocks gradually break down due to erosion. 
Rivers flowing through these regions carry along the eroded rock 
pieces. As the rivers flow, they continue to break down the rocks 
further into pebbles, stones, sand; and transport large quantities 
of them to the plains.
The bigger rocks are eventually broken down into finer grains 
of sand and clay. Is this grain the smallest unit of a bigger rock 
or can these grains of sand and clay be broken down further? 
Let us find out!
7.1 What Is Matter Composed of?
    Activity 7.1: Let us explore
 z Take a stick of chalk (Fig. 7.1a) and break it into two 
pieces (Fig. 7.1b). 
 z Continue breaking the chalk till it becomes difficult 
to break it further by hand.
 z Grind the small pieces of chalk thus obtained 
(Fig. 7.1c) using mortar and pestle.
 z Observe the fine powder of chalk with a magnifying 
glass (Fig. 7.1d).
 z What do you observe?
 z Each tiny grain you observe is still a speck of chalk.               
Is every speck of this fine 
chalk powder still composed 
of the same substance, 
or has it changed into 
something else on breaking 
or grinding?
Recall Curiosity, Grade 7 chapter ‘Changes Around 
Us: Physical and Chemical’— is grinding chalk a physical 
change or a chemical change? You learnt that the chalk 
does not change into a new substance on grinding. It is a 
physical change in which only the size of each speck of 
chalk has reduced further.
(a)
(b)
(c) 
(d)
Fig. 7.1: (a) A stick of 
chalk; (b) The chalk stick 
broken into two pieces; 
(c) A piece of chalk 
ground into fine powder; 
(d) A close-up view of 
chalk powder under a 
magnifying glass 
Chapter 7.indd   99 Chapter 7.indd   99 6/28/2025   2:52:45 PM 6/28/2025   2:52:45 PM
100
Curiosity — Textbook of Science for Grade 8
These specks of chalk powder can be broken further into 
smaller particles by further grinding. Let us imagine that this 
process of grinding continues. Eventually, we would reach a stage 
where the chalk particles cannot be broken down any further. 
The tiny units obtained at this stage 
are the basic building blocks that the 
chalk was made up of. 
This means that one whole piece of 
chalk was made up of a large number 
of smaller units. These units are called 
constituent particles of chalk. A constituent particle is the basic 
unit that makes up a larger piece of a substance or material. Just 
like chalk, the grains of sand and clay are not the smallest units 
of bigger rocks. These are also made up of a large number of 
their constituent particles.
Let us explore further!
Recall the dissolution of sugar into water to form a solution. 
What happens to sugar when it is dissolved in water?
Activity 7.2: Let us perform
 z Fill a glass tumbler with 
drinking water. 
 z Put two teaspoons of sugar 
into it.
 z Do not stir the water. Taste a 
small spoonful of water from 
the top layer of the glass.
Does the water taste sweet? 
 z Now, stir the water until the sugar dissolves completely 
(Fig. 7.2). 
 z Again taste a spoonful of water from the top layer.
What difference in taste do you notice? Does it taste sweet? 
Since the top layer of water tastes sweet after dissolving 
sugar, it must be present in the solution. Do you observe any 
sugar particles in the solution? 
Sugar particles can no longer be observed but their 
presence can be sensed by taste. When sugar dissolves in 
water, it breaks up into its constituent particles which cannot 
be broken down further. Each tiny grain of sugar is made up 
of millions and millions of such constituent particles.
Are the units of chalk 
obtained in this manner 
considered the smallest 
units of chalk?
Fig. 7.2: Dissolving 
sugar in water
Safety first
Perform the activity under the 
supervision of a teacher or an adult. 
Never eat or drink anything unless 
asked to.
Chapter 7.indd   100 Chapter 7.indd   100 6/28/2025   2:52:49 PM 6/28/2025   2:52:49 PM
Chapter 7?—?Particulate Nature of Matter
101
Activities 7.1 and 7.2 support the idea that matter is composed 
of a large number of extremely small particles. These particles 
are so small that they cannot be seen even through an ordinary 
microscope.
But, where did 
the sugar go?
The tiny sugar particles separate and occupy the available 
spaces between the water particles. These spaces between the 
particles are known as interparticle spaces. 
Chalk and sugar can both 
be broken down into their 
constituent particles. But how 
are the constituent particles 
held together to form the solid 
pieces we see?
7.2 What Decides Different States of Matter?
The constituent particles of matter are held together through 
forces which are attractive in nature. These forces are called 
interparticle attractions. The strength of these attractions 
depends on the nature of the substance and the interparticle 
distance. Even a slight increase in the distance decreases the 
interparticle forces drastically. The strength of these forces 
ultimately decides the physical state of the substances.
Do you know that since ancient times, people have been thinking 
about how far things could be broken down and what is matter 
made up of?
 Acharya Kanad, an ancient Indian philosopher, first spoke 
about the idea of a Parmanu (atom). He believed that matter is 
made up of tiny, indivisible eternal particles called Parmanu. 
This idea was written in his work called Vaisheshika Sutras. 
Our scientific heritage
Chapter 7.indd   101 Chapter 7.indd   101 6/28/2025   2:52:56 PM 6/28/2025   2:52:56 PM
Page 5


98
Curiosity — Textbook of Science for Grade 8
Particulate Nature 
of Matter 
7
 
 z Why is it possible to pile up stones or sand, but not a liquid like 
water?
 z Why does water take the shape of folded hands but lose that 
shape when released?
 z We cannot see air, so how does it add weight to an inflated 
balloon?
 z Is the air we breathe today the same that 
existed thousands of years ago?
 z Share your questions 
  ?
Probe and ponder
Chapter 7.indd   98 Chapter 7.indd   98 6/28/2025   2:52:43 PM 6/28/2025   2:52:43 PM
Chapter 7?—?Particulate Nature of Matter
99
You might have collected pebbles and stones from the sand while 
playing on a riverbank or a beach. Where do these pebbles, 
stones, and sand come from? 
In the mountains, rocks gradually break down due to erosion. 
Rivers flowing through these regions carry along the eroded rock 
pieces. As the rivers flow, they continue to break down the rocks 
further into pebbles, stones, sand; and transport large quantities 
of them to the plains.
The bigger rocks are eventually broken down into finer grains 
of sand and clay. Is this grain the smallest unit of a bigger rock 
or can these grains of sand and clay be broken down further? 
Let us find out!
7.1 What Is Matter Composed of?
    Activity 7.1: Let us explore
 z Take a stick of chalk (Fig. 7.1a) and break it into two 
pieces (Fig. 7.1b). 
 z Continue breaking the chalk till it becomes difficult 
to break it further by hand.
 z Grind the small pieces of chalk thus obtained 
(Fig. 7.1c) using mortar and pestle.
 z Observe the fine powder of chalk with a magnifying 
glass (Fig. 7.1d).
 z What do you observe?
 z Each tiny grain you observe is still a speck of chalk.               
Is every speck of this fine 
chalk powder still composed 
of the same substance, 
or has it changed into 
something else on breaking 
or grinding?
Recall Curiosity, Grade 7 chapter ‘Changes Around 
Us: Physical and Chemical’— is grinding chalk a physical 
change or a chemical change? You learnt that the chalk 
does not change into a new substance on grinding. It is a 
physical change in which only the size of each speck of 
chalk has reduced further.
(a)
(b)
(c) 
(d)
Fig. 7.1: (a) A stick of 
chalk; (b) The chalk stick 
broken into two pieces; 
(c) A piece of chalk 
ground into fine powder; 
(d) A close-up view of 
chalk powder under a 
magnifying glass 
Chapter 7.indd   99 Chapter 7.indd   99 6/28/2025   2:52:45 PM 6/28/2025   2:52:45 PM
100
Curiosity — Textbook of Science for Grade 8
These specks of chalk powder can be broken further into 
smaller particles by further grinding. Let us imagine that this 
process of grinding continues. Eventually, we would reach a stage 
where the chalk particles cannot be broken down any further. 
The tiny units obtained at this stage 
are the basic building blocks that the 
chalk was made up of. 
This means that one whole piece of 
chalk was made up of a large number 
of smaller units. These units are called 
constituent particles of chalk. A constituent particle is the basic 
unit that makes up a larger piece of a substance or material. Just 
like chalk, the grains of sand and clay are not the smallest units 
of bigger rocks. These are also made up of a large number of 
their constituent particles.
Let us explore further!
Recall the dissolution of sugar into water to form a solution. 
What happens to sugar when it is dissolved in water?
Activity 7.2: Let us perform
 z Fill a glass tumbler with 
drinking water. 
 z Put two teaspoons of sugar 
into it.
 z Do not stir the water. Taste a 
small spoonful of water from 
the top layer of the glass.
Does the water taste sweet? 
 z Now, stir the water until the sugar dissolves completely 
(Fig. 7.2). 
 z Again taste a spoonful of water from the top layer.
What difference in taste do you notice? Does it taste sweet? 
Since the top layer of water tastes sweet after dissolving 
sugar, it must be present in the solution. Do you observe any 
sugar particles in the solution? 
Sugar particles can no longer be observed but their 
presence can be sensed by taste. When sugar dissolves in 
water, it breaks up into its constituent particles which cannot 
be broken down further. Each tiny grain of sugar is made up 
of millions and millions of such constituent particles.
Are the units of chalk 
obtained in this manner 
considered the smallest 
units of chalk?
Fig. 7.2: Dissolving 
sugar in water
Safety first
Perform the activity under the 
supervision of a teacher or an adult. 
Never eat or drink anything unless 
asked to.
Chapter 7.indd   100 Chapter 7.indd   100 6/28/2025   2:52:49 PM 6/28/2025   2:52:49 PM
Chapter 7?—?Particulate Nature of Matter
101
Activities 7.1 and 7.2 support the idea that matter is composed 
of a large number of extremely small particles. These particles 
are so small that they cannot be seen even through an ordinary 
microscope.
But, where did 
the sugar go?
The tiny sugar particles separate and occupy the available 
spaces between the water particles. These spaces between the 
particles are known as interparticle spaces. 
Chalk and sugar can both 
be broken down into their 
constituent particles. But how 
are the constituent particles 
held together to form the solid 
pieces we see?
7.2 What Decides Different States of Matter?
The constituent particles of matter are held together through 
forces which are attractive in nature. These forces are called 
interparticle attractions. The strength of these attractions 
depends on the nature of the substance and the interparticle 
distance. Even a slight increase in the distance decreases the 
interparticle forces drastically. The strength of these forces 
ultimately decides the physical state of the substances.
Do you know that since ancient times, people have been thinking 
about how far things could be broken down and what is matter 
made up of?
 Acharya Kanad, an ancient Indian philosopher, first spoke 
about the idea of a Parmanu (atom). He believed that matter is 
made up of tiny, indivisible eternal particles called Parmanu. 
This idea was written in his work called Vaisheshika Sutras. 
Our scientific heritage
Chapter 7.indd   101 Chapter 7.indd   101 6/28/2025   2:52:56 PM 6/28/2025   2:52:56 PM
102
Curiosity — Textbook of Science for Grade 8
Let us explore how these attractions vary in different states.
7.2.1 Solid state
How are constituent particles held together in solids?
Activity 7.3 : Let us find out
 z Collect a few solid objects, such as a piece 
of iron or an iron nail, a piece of rock salt, 
a stone, a piece of wood, a key, and a piece 
of aluminium (Fig. 7.3). 
 z Observe their shapes and sizes.
 z Try hammering them.
 z In which of the above six objects do 
you think particles are strongly held  
together?
You must have noticed that all these 
objects are solids. They have a definite shape 
and volume. This is due to the fact that in solids, the particles 
are tightly packed and the interparticle attractions are very 
strong. These strong forces of attraction hold the particles in 
fixed positions, preventing them from moving freely (Fig. 7.4a). 
The particles can only move to and fro about their 
positions (vibrate or oscillate) but cannot move 
past each other.
When solids are heated, their particles vibrate 
more vigorously (Fig. 7.4b). A stage is reached 
when these vibrations become so vigorous that the 
particles start leaving their position. The interparticle forces of 
attraction get weakened and the solid gets converted into the 
liquid state (Fig. 7.4c). The temperature at which this happens is 
the melting point of the solid. 
Fig. 7.4: Magnified schematic pictures of melting of a solid
(b) Particles with 
increased vibrations
(a) Solid (c) Liquid
Stone
Piece of aluminium
Rock salt
Key
Iron nail
Wooden block
Fig. 7.3: Some solid objects
In the solid state, 
is there any way 
to move these 
particles apart? 
Chapter 7.indd   102 Chapter 7.indd   102 6/28/2025   2:53:00 PM 6/28/2025   2:53:00 PM