Page 57 - ICSE Chemistry 6

STATES OF MATTER

We have learnt that all substances are made of ma er. Let's now understand what does ma er consist
of. Ma er is made up of very ny par cles called atoms. An atom usually does not exist independently.
An atom is the smallest possible unit of ma er that exhibits all its proper es. The atoms combine to form
molecules. A molecule is the smallest par cle of ma er. It has an independent existence and also exhibits
all the proper es of ma er.

Example: Elements like oxygen, gold, etc. are made of the same types of atoms.
O + O O O

O + O O
2
Compound like H O are made up of two diff erent atoms.
2
O
H + O + H
H H
H + O + H H O
2

Composition and Properties of Matter

All substances are made up of molecules. The way these molecules are held together determines their
state of ma er. Ma er exists in three states—solid, liquid and gas. These three states are diff erent because
the molecules present in them are arranged in diff erent ways. The molecular arrangement in diff erent
states of ma er is such that there is always some space (distance) between the molecules which is known
as the interpar cular or intermolecular space (distance). Also, the molecules are very small and cannot be
seen even under the microscope. These molecules a ract each other with a force called intermolecular
force of a rac on. The force of a rac on between par cles of the same kind of molecules is known as
cohesive force.

The intermolecular force of a rac on and the intermolecular space (distance) are responsible for
determining the state of ma er. The intermolecular force of a rac on decreases as the intermolecular
space between the molecules increases.

Thinking Fountain
Thirst for Knowledge In case of solids the molecules are ghtly packed. As
the space between the molecules is very less, the
Plasma is considered as the fourth state of a rac on between the molecules increases. Hence,
ma er. It is an ionised gas which consists of intermolecular force between the molecules of a solid
both nega vely charged par cles and posi vely increases as the intermolecular space decreases.
charged par cles. The ma er in the sun exists in
What do you think will be the rela onship between
the form of plasma. Like other gases plasma also
intermolecular space and intermolecular force in case
does not have a fi xed shape and volume. of gases?

At ordinary temperature and pressure, ma er exists in three states based on the arrangement of par cles
or molecules.

• Solid • Liquid • Gas

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