Page 17 - ICSE Chemistry 8

Liquids

The molecules in liquids are less closely packed to each other as
compared to solids and more closely packed in comparison to gases.
The intermolecular space in liquids is more than solids. Therefore, the
intermolecular force of a rac on between the molecules is less than
that in solids but more as compared to gases. The molecules in liquids
are compara vely free to move; they move from one posi on to the
other within the liquid. That is the reason that liquids have the ability to
fl ow. The kine c energy is s ll not suffi cient to overcome the a rac ve
forces. However, the addi on of a small amount of energy can make the Fig. 1.2: Liquids consisting of less
par cles move away from each other. Due to this reason, liquids tend to tightly packed molecules
evaporate when le exposed to air.

Gases

The molecules in gases are far from each other and the intermolecular
space is the largest in comparison to liquids and solids. Therefore the
intermolecular force of a rac on is negligible in gases. The par cles in
gases are not arranged in a fi xed order and keep moving randomly in
the available space. The kine c energy of the par cles is suffi cient to
overcome the interpar cle force of a rac on thus enabling the par cles Fig. 1.3: Gases consisting of
to move away from each other. loosely held molecules

Take a Break!

Fill in the blanks.
1. ___________ have fi xed shape and volume.

2. The atoms/molecules are in constant mo on and hence possess _____________.
3. The state of ma er is decided on the basis of _____________________ and __________________
between the par cles of ma er.
4. ___________________ explains the behaviour of ma er in diff erent states.

5. The interpar cle force of a rac on is ____________ in gases.

STATES OF MATTER

The change of state of ma er depends on the intermolecular space between their molecules and
intermolecular force present between the par cles of solids, liquids
and gases. It also depends on the collision between the molecules of
Thinking Fountain
the three states of ma er.
Why do solids have defi nite
Let’s study the proper es of states of ma er. size and shape but liquids and
gases don’t?

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