Page 89 - Innovator's Science-8

and hold the particles tightly together, while in liquids, the forces are
Science weaker and let particles slide past one another. In gases, the forces are very
Bytes

weak, so particles move freely and stay far apart.
Testimony
Acharya Kanad, an
ancient Indian SOLID STATE
philosopher, was the first How are constituent particles held together in solids?
to talk about the idea of a
Parmanu, which means
atom. He believed that
everything in the world is
made up of ny,
indivisible par cles called Iron nail Rock salt Stone Wooden block Key Piece of aluminium
Parmanu that cannot be Some solid objects
broken down further. He
thought these par cles When collecting solid objects like a piece of iron, an iron nail, rock salt,
were eternal and invisible stone, wood, a key, and aluminum, you will see that all have a fixed shape
to the naked eye. Kanad and size. These are solids, and the reason for their definite shape and
also explained that
Parmanu could combine volume is that their particles are tightly packed together with very strong
with each other in forces holding them in place. These forces, called interparticle attractions,
different ways to form keep the particles fixed so they cannot move freely but only vibrate slightly
everything around us. His
ideas were wri en in a in their positions. When you try hammering these solids, it's these strong
work called Vaisheshika forces that give them strength and shape. When solids are heated, their
Sutras, where he founded
the Vaisheshika School of particles vibrate more
philosophy to teach and more until the
about atoms and the
nature of the universe. vibrations become so
This concept of Parmanu strong that particles
by Acharya Kanad is start to move away
considered one of the a. Solid b. Particles with c. Liquid
earliest ideas about from their fixed increases vibrations
atoms in the world, even positions, weakening Magnified schematic pictures of melting of a solid
before modern atomic
theory was developed. the forces. This causes the solid to melt and turn into a liquid, and the
Let us explore how these temperature at which this happens is called the melting point of that solid.
a rac ons vary in So, the way particles are held together and how much they can move
different states.
determines whether a substance is solid or liquid.

The minimum temperature at which a solid melts to become a liquid at the
atmospheric pressure is called its melting point . Generally, in a liquid state,
particles are somewhat farther away from each other as compared to those

in the solid state (ice is an exception—its particles are farther apart than
those in water). Some solids have weak interparticle forces of attraction, so
their melting points are low. While others have strong attractive forces and

have high melting points. Some examples of solids and their melting points
are shown on the next page.

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