Ionic bonding: properties of compounds and naming

In a nutshell

An ionic bond is formed when metal atoms donate electrons to non-metal atoms. This movement of electrons can be represented by dot and cross diagrams.

Ionic bonds

Definition

An ionic bond forms when a metal atom donates electrons to a non-metal atom. The metal atom will form a positive ion and the non-metal atom will form a negative ion. The opposite charges between ions form electrostatic forces.

Dot and cross diagrams

These diagrams are used to show the electrons of the metal and non-metal atom in an ionic bond. Dot and cross diagrams are used to show the movement of electrons from the metal atom to the non-metal atom.

Example

Chemistry; Key concepts; KS4 Year 10; Ionic bonding: properties of compounds and naming

The sodium atom (metal atom) will donate its one outer shell electron. A single positively charged ion is formed, $Na^+$ . The chlorine atom (non-metal atom) accepts the single electron from the sodium atom, forming a single negatively charged ion, $Cl^-$ .

Properties of ionic compounds

Lattice structure

Ionic compounds have giant ionic structures.
Ionic compounds contain a regular lattice structure of repeated ions.
Lattice structure is filled with alternating positive and negative ions.
An ionic bond is held together by electrostatic forces of attraction between oppositely charged ions.

Chemistry; Key concepts; KS4 Year 10; Ionic bonding: properties of compounds and naming

Melting and boiling points

Strong electrostatic forces of attraction.
High amounts of energy are needed to break the forces in an ionic compound, this leads to high melting and boiling points.

Conductivity

Solid ionic compounds do not contain any free ions, so will not conduct electricity.
The lattice ion structure in a ionic compound will break down when melted and the ions are free to move, carrying an electrical charge (conducts electricity).

Solubility in water

Soluble in water (dissolves easily).
Ions in an ionic compound break down when placed in water and will carry an electrical charge.

Naming ionic compounds

The formula of the ions present in the ionic compound are needed in order to deduce the formula of the ionic compound.

Note: If the ionic compound contains only two elements its name will end with '-ide', more than two elements its name will end with '-ate'.

Example

Calcium carbonate ( $CaCO_3$ ), ends with an -ate as there are three elements in the ionic compound.

Example

Work out the formula for the ionic compound, potassium iodide.

Potassium iodide contains potassium atoms ( $K$ ) and iodine atoms ( $I$ ). Potassium atoms form $K^+$ ions and iodine atoms form $I^-$ ions. The charges are equal and balanced, so the formula for

potassium iodide is $\underline{KI}$ .