6.2 Physical State and Melting Points

6.2 Physical State and Melting Points

6.2.1 Solids at STP

At Standard Temperature and Pressure (STP), salts are usually solids. This is due to the strong electrostatic forces of attraction between the oppositely charged ions, which form a tightly bound lattice structure. These forces require significant energy to overcome, resulting in high melting points.

6.2.2 Lattice Structure of Ionic Compounds

Under normal conditions, ionic compounds are usually solids with a well- defined lattice structure. This property is due to the nature of the ionic bonds that hold the ions together. Ionic bonds are formed by electrostatic attraction between positively charged ions (cations) and negatively charged ions (anions). These ions are arranged in a repeating three- dimensional pattern called a crystal lattice. This arrangement maximizes the electrostatic attractions and minimizes the repulsions between ions, leading to a stable structure.

6.2.3 Electrical Conductivity

Molten and aqueous solutions of salts are good conductors of electricity because of the presence of free- moving ions.

When salts are in their solid state, their ions are held together in a rigid lattice structure by strong ionic bonds. In this state, the ions are not free to move, so solid salts do not conduct electricity. Upon melting, the rigid lattice breaks down due to the high temperature. The ions become free to move in the molten state. These free- moving positive (cations) and negative (anions) ions can carry electrical charge, allowing the molten salt to conduct electricity.