Page 88 - Innovator's Science-8

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.
These specks of chalk powder can be broken further into smaller particles
Science by further grinding. Let us imagine that this process of grinding continues.
Bytes
Eventually, we would reach a stage where the chalk particles cannot be
Testimony
A single spoon of sugar broken down any further. The tiny units obtained at this stage are the
contains billions of ny basic building blocks that the chalk was made up of. This means that one
par cles that are too whole piece of chalk was made up of a large number of smaller units.
small to be seen with our
eyes. If chalk is ground These units are called constituent particles of chalk. A constituent particle
again and again, a stage is the basic unit that makes up a larger piece of a substance or material.
comes when it cannot be
broken further - these Just like chalk, the grains of sand and clay are not the smallest units of
smallest units are the bigger rocks. These are also made up of a large number of their
basic building blocks of constituent particles.
ma er. When sugar
dissolves in water, it does Recall the dissolution of sugar into water to form a solution. What happens
not vanish; it simply to sugar when it is dissolved in water?
spreads so finely that it
becomes invisible, yet its When sugar dissolves in water, the tiny sugar particles break off from the
sweetness proves that it solid sugar crystals and mix into the water. The water molecules surround
is s ll present in the
solu on. There are small each sugar particle and pull it away from the other sugar particles, helping
empty spaces between it to spread out and disappear into the water. The sugar does not vanish—it
the par cles of ma er,
and these spaces allow just breaks up so small that it cannot be seen, but it is still there,
other par cles to move in sweetening the water and forming a solution. This shows that there are
between. The strength of small spaces between the water particles where the sugar fits in and mixes
the forces of a rac on
between the par cles completely.
decides whether a
substance exists as a It supports the idea that matter is composed of a large number of
solid, liquid, or gas. extremely small particles. These particles are so small that they cannot be
seen even through an ordinary microscope. The tiny sugar particles
separate and occupy the available spaces between the water particles.

These spaces between the particles are known as interparticle spaces .

WHAT DECIDES DIFFERENT STATES OF MATTER?

The particles that make up matter are held together by attractive forces
called interparticle forces . These forces act between the particles and pull
them towards each other. The strength of these forces depends on the kind
of substance and how far apart the particles are. If the distance between

the particles increases even a little, the attractive forces become much
weaker very quickly. These forces are important because they decide
whether a substance is a solid, liquid, or gas. In solids, the forces are strong

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Science-8