Q. Describe Structure of Solids?

Ans.

Solids are different from gases and liquids because they have a fixed shape. This definite shape occurs as the individual particles which make up the solid are fixed in position. Most solids are crystalline solids and have a well-defined crystal structure.

Solids can be composed of three types of particles: atoms, molecules, and ions. The three types of solids have very different properties because the attractive forces that hold the crystal together are different.

There are a few solids, such as glass and paraffin, which have definite shape and volume but have no definite internal structure or form. Such solids are called amorphous solids.

The structure of solids can be best described with a crystal structure system. A unit cell (refer to figure below) is the smallest block-like unit from which the larger crystal can be built.

As illustrated below, there are three kinds of unit cells: simple cubic, body-centered cubic, and face-centered cubic. The simple cubic unit cell looks like an empty cube. The body-centered cubic unit cell has a single atom within the cube.

The four kinds of crystalline solids that will be discussed in the next section are:

• Metallic solids
• Covalent network solids
• Molecular solids
• Ionic solids