STATES OF MATTER
The Physical Status of Matter
There are mainly three different kinds of the physical states of matter,
namely:
- Solid
- Liquid
- Gas
Plasma a fourth class of matter has also been identified. These states of
matter are also termed as phases.
1) Solid : Solids are characterized by their definite shape and also
their considerable mechanical strength and rigidity. Solids tend to resist the
deformation of their shape due to strong intra molecular forces and absence of
the translatory motion of the structural units (atoms, ions etc). A solid is
relatively non compressible, i.e. temperature and pressure have only a slight
effect on its volume.
Solids are broadly classified as crystalline or amorphous.
Crystalline solids : Here the atoms are arranged in a definite pattern
which is constantly repeated.
Amorphous solids : These have no definite geometrical form.
2) Liquid : A liquid has no definite shape and it takes the shape of
the vessel containing it. Like solids, the volume of a liquid is slightly
altered by variations in temperature and pressure. Liquids have three typical
physical properties, namely:
i) Vapor pressure : A Liquid when kept in a closed container vaporizes
into the free space above it. The process of vaporization will continue till the
equilibrium is reached between liquid and vapor. The pressure at which the
liquid and vapor can co-exist is called the vapor pressure of the liquid at a
given temperature.
ii) Surface tension : The surface of a liquid is always in a state of
tension because a molecule at the surface is attracted towards the bulk by a
force much greater than that drawing it toward the vapor where the attracting
molecules are more widely spread. Due to this, a certain force is required to
penetrate along any line in the surface. This force is called surface tension.
iii) Viscosity : It determines the flow of the liquid. It is the
internal friction between layers of the liquid. Higher the rate of friction,
greater the viscosity of the liquid and its flow will be retarded. Conversely, a
lower rate of friction lessens the viscosity and makes the liquid more fluid.
3) Gases : A gas has no bounding surface at all and will occupy
completely any vessel in which it is filled. It has no definite volume or shape
and can be easily expanded or compressed.
Laws governing behavior of gases will be dealt with in detail in
the next chapter.
Water is the ideal example to show the different states of matter.
Water when cooled to 00C becomes solid. When the temperature of
solid water is raised it becomes liquid. If the liquid is heated to 1000C
it gets converted to steam or vapor (The Gas phase).
Almost all chemical substances can exist in more than one physical state
(phase) depending on external pressure and temperature.
The following table illustrates different states of matter and their physical
properties.
Table 9
| |
Property |
States of matter |
| |
|
Solid |
Liquid |
Gas(Vapor) |
|
i) |
Shape |
definite |
indefinite |
indefinite |
|
ii) |
Volume |
definite |
definite |
indefinite |
|
iii) |
Molecular
Bonding |
very strong |
strong |
Weak |
|
iv) |
Examples |
NaCl
ZnSO4 |
H2O
Petrol |
H2 , CO2
LPG |
| |
|
The Molecular mode of Solids, Liquids, Gases
Plasma : This is the fourth state of matter. It is a type of gas
containing positively and negatively charged particles in approximately equal
numbers and present in the sun and most stars.
|
