Solid is one of the three main states of matter, along with liquid and gas

Solid is one of the three main states of matter, along with liquid and gas.

In a solid state, particles are "packed" closely together and are not free to move about within the substance. Molecular motion for the particles in a solid is confined to very small vibrations of the atoms around their fixed positions. Conclusion is this - solids have a fixed shape that is difficult to change. Also, solids have a definite volume.

There are two main categories of solids - crystalline solids and amorphous solids. Crystalline solids are those in particles exist in a regular and well-defined arrangement. The smallest repeating pattern of crystalline solids is known as the unit cell. The others are called the amorphous solids. Amorphous solids do not have much order in their structures. Common examples of this type of solid are glass and plastics.

There are four types of crystalline solids:

Ionic solids - Made up of positive and negative ions and held together by electrostatic attractions - NaCl.

Molecular solids - Made up of atoms or molecules held together by London dispersion forces, dipole-dipole forces, or - sucrose.

Atomic solids - Made up of atoms connected by covalent bonds. Examples of this type of solid are diamond and graphite, and the fullerenes.

Metallic solids - Made up of metal atoms that are held together by metallic bonds.