The three states of matter : solid, liquid and gas are the result of competitive molecular interaction and thermal energy.
For any substance to be in a particular state of matter is a matter of strength of intermolecular forces which when strongest bring the molecules closest (as much as possible) and substance adopts definite volume and shape at room temperature.
The same substance at three different temperatures:
(i) Temperature below its melting point (m.p.).
(ii) Temperature above its m.p. but below b.p.
(iii) Above its b.p.
In solid state, the atoms are arranged in an orderly manner and are at fixed positions. There is only one form of molecular motion in solids, namely, vibration motion, by virtue of which the particles move about their fixed positions and cannot easily leave the solid surface.
Solids can be classified in two major categories on the basis of pattern of arrangement of constituent particles.
(a) Crystalline Solid; (b) Amorphous Solid
(a) Crystalline Solid: Solids in which constituent particles are arranged in a well and long range ordered pattern. e.g. Salt, Diamond, Iodine, etc.
(b) Amorphous Solid: Solids in which pattern is short range ordered or disordered. e.g. Plastic, Glass, Rubber etc. Amorphous solid are also known as super cooled liquid.
Difference between Crystalline and Amorphous Solid
|Property ||Crystalline Solid ||Amorphous Solid |
|1. Crystal |
|These have definite crystal |
shapes because of ordered
|Do not have definite |
geometrical shape because
of irregular arrangement
|2. Symmetry ||These can have |
(a) plane of symmetry
(b) center of symmetry
(c) axis of symmetry.
|Do not have any symmetry. |
|3. Anisotropic or |
|In these, some properties are |
direction dependent e.g.
refractive index i.e., these are
|Properties are not direction |
dependent i.e.these are ,
|4. Melting Point ||Sharp M.P. ||These have range of melting |
|5. Physical State ||Hard and rigid ||Soft |
|6. Crystal System ||These have seven types of |
definite crystal systems.
|These do not have regular |
Crystalline solids are classified on the basis of interparticle forces.
|Types of Solid ||Constituent particle ||Nature of Forces || Examples |
|Positive and Negative |
|Electrostatic forces ||Ionic compounds |
|2. Covalent ||Covalently bonded |
|Covalent forces in |
3D cross network
|3. Metallic ||Metal ions (kernels) |
surrounded by mobile
|Metallic bonds ||Metals and some alloys |
|4. Molecular ||Molecules ||van der Waal forces ||12, solid C02, Ice, Sulphur |
Note: In this chapter, when we will be talking about solids, it must be understand to be crystalline only.