# Explain the term solids

A solid can be defined as a substance that exists in the solid-state, which is one of the four fundamental states of matter. All solids have rigid structures that tend to resist any external forces applied to them. Solids also are known to have a fixed, definite shape.

## Types of Solids

### Crystalline Solids

A crystalline solid (also known as a crystal) is a solid in which the constituent atoms or molecules are arranged in a highly ordered microscopic structure. Common examples of crystalline solids include ice, sodium chloride (table salt), potassium chloride, and diamonds.

• Crystalline solids give a regular cut when cut with a sharp-edged knife
• Crystalline solids are rigid, and mild distorting forces do not distort their shape
• Crystalline solids are anisotropic. This implies that physical properties such as refractive index, conductivity, thermal expansion etc., are different in different directions.

### Amorphous solids

An amorphous solid is a substance whose constituent particles do not possess a regular, orderly arrangement, e.g. glass, plastics, rubber, starch, and proteins.

• They do not have sharp melting points.
• Amorphous solid are not very rigid. These can be distorted by bending or compressing forces.
• Amorphous solids are isotropic in nature. This implies that various physical properties are the same in all directions. This is because of the random arrangement of particles.