Ionic Structures

Introduction to Ionic Bonds

An ionic bond is formed when electrons are completely transferred from one atom to another.
The atom losing electrons becomes a positively charged ion (or cation) and the atom gaining these electrons becomes a negatively charged ion (or anion).
Ionic compounds consist mainly of metals and non-metals. The metal atoms lose electrons to form cations and the non-metal atoms gain these electrons to form anions.

Formation of Ionic Compounds

For example, consider sodium (Na) and chlorine (Cl). Sodium loses one electron to attain a stable electron configuration, becoming Na+. Chlorine gains this electron to become Cl-. The resulting compound (sodium chloride, NaCl) is held together by the attraction between these oppositely charged ions.

Structure of Ionic Compounds

Ionic compounds such as sodium chloride form a giant ionic lattice structure. This involves a repeating pattern of ions, extending in all three spatial dimensions.
The structure is held together by strong ionic bonds in all directions, giving ionic compounds high melting and boiling points.

Properties of Ionic Compounds

Ionic compounds are usually solid at room temperature due to their giant ionic structures.
They generally have high melting and boiling points because a lot of energy is required to break the strong ionic bonds in the lattice structure.
When dissolved in water or melted, ionic compounds conduct electricity. The free moving ions can carry electrical charge.
They are often soluble in water, as water molecules can separate the ions.

Arrangement of Ions

In a sodium chloride structure, each sodium ion is surrounded by six chloride ions, and vice versa. This maximises the attractions between the positive and negative ions and therefore increases the stability of the structure.
The empirical formula (the simplest ratio of atoms in a compound) for ionic compounds does not show the actual number of ions in the lattice. For instance, the formula for sodium chloride is NaCl, demonstrating a 1:1 ratio of sodium ions to chloride ions.

Limitations of Dot-and-Cross Diagrams

Dot-and-cross diagrams are often used to demonstrate the ionic bonding in compounds. They show the outer shell electrons of the atoms involved in the bond.
However, these diagrams do not depict the actual layout of ions in the giant ionic structure or show the scale of ionic compounds.
They also don’t represent the high melting and boiling points or ability to conduct electricity that result from the structure of the ionic compound.