General Characteristics of Solid State

In Class XI you learnt that matter exists in three physical states — solid, liquid and gas. Which of these is the most stable for a given substance, at a particular temperature and pressure, is decided by the tug-of-war between two opposing factors:

• Intermolecular forces, which pull the constituent particles (atoms, ions or molecules) together and try to hold them close.
• Thermal energy, which keeps the particles moving and tends to drive them apart.

When the temperature is low enough, the thermal energy is small and the intermolecular forces dominate. The particles are drawn so close that they cling to one another and settle into fixed positions. They are not completely frozen — they can still oscillate about their mean positions — but they can no longer wander freely. This is the solid state.

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Characteristic properties of solids

• They have a definite mass, volume and shape.
• The intermolecular distances are short.
• The intermolecular forces are strong.
• The constituent particles occupy fixed positions and can only oscillate about their mean positions.
• They are incompressible and rigid.