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Ionic bonds

The ionic bond

An ionic bond is a chemical bond where electrons are completely transferred from one atom (or group of atoms) to another. This bond typically occurs between metals and non-metals.

This is unlike a covalent bond, where two non-metallic atoms share electrons.

Atoms will gain or lose electrons to satisfy the octet rule.

Metal atoms tend to lose their valence electrons to form cations. A cation is a positively-charged ion that has more protons than electrons, resulting in an overall positive charge.

Non-metal atoms usually gain electrons from metal atoms to form anions. An anion is a negatively-charged ion that has more electrons than protons, resulting in an overall negative charge.

The positive and negative ions are attracted to one another because of electrostatic forces. The attraction between these positive and negative ions is the basis for ionic bonding.

A 2D representation of sodium chloride (table salt). Sodium chloride crystals consist of chloride anions and sodium cations arranged in a lattice.

Ionic lattice structures

In solid form, an ionic compound consists of a giant lattice structure of ions. Electrostatic forces of attraction hold the ions in a fixed position in a well-ordered grid.

The electrostatic force is the attraction between two oppositely charged particles. The ionic lattice is formed by electrostatic forces between anions and cations.

When table salt ($\ce{NaCl}$) is in solid form, the positive sodium cations and negative chloride anions are held in a lattice structure.

The larger green spheres represent chloride ions while the smaller blue spheres represent the sodium ions.

Ionic compounds tend to be solids at room temperature due to their high melting and boiling points.

They have high melting points and boiling points because a lot of energy is needed to overcome the strong electrostatic forces between all the ions.

Magnesium oxide ($\ce{MgO}$) is used to line the inner surfaces of furnaces as it is able to withstand high temperatures.

Conductivity of ionic compounds

Ionic compounds do not conduct electricity and heat well in the solid state. These compounds only conduct electricity when in liquid state or when dissolved in water.

Electrical conductivity depends on the presence of mobile charged particles.

Conductivity in ions is low in the solid state because the ions are locked in the lattice and unable to move. In the liquid or aqueous state, ionic compounds consist of free flowing ions.

Liquid and aqueous ionic compounds are conductors of electricity because they have mobile charge carriers (in the form of the ions).

The beaker of copper (II) sulfate solution completes this circuit, so electricity can flow and the bulb lights up.