Ionic Compound

Key Stage 4

An ionic compound is a molecule formed from 2 or more elements which have transferred electrons to become ions.

Ionic compounds form when atoms lose one or more electrons to become a positive ions and other atoms gain electrons to become negative ions. The electrostatic force of attraction between these ions is a strong chemical bond.

Metal elements form positive ions because it is easier for them lose electrons than gain electrons to get a full outer shell. Metals are on the left hand side of the Periodic Table and usually have either 1, 2, 3 or 4 electrons in the Outer Shell.

Group 1 Elements all form +1 ions; Li⁺¹, Na⁺¹, K⁺¹

Group 2 Elements all form +2 ions; Be⁺², Mg⁺², Ca⁺²

Group 3 Elements all form +3 ions; Al⁺³

Transition Metal Elements can form different ions which are shown by Roman Numerals; Iron can form Fe(II) which is Fe⁺² or Fe(III) is Fe⁺³,

Non-metal elements form negative ions because it is easier for them to gain electrons than lose electrons to get a full outer shell. Non-metals are on the right hand side of the Periodic Table and usually have 4, 5, 6, 7 or 8 electrons in their outer shell.

Group 5 Elements all form -3 ions; N^-3, P^-3

Group 6 Elements all form -2 ions; O^-2, S^-2

Group 7 Elements all form -1 ions; F^-1, Cl^-1

Some covalent compounds can form negative ions; Carbonate forms -2 ions CO₃^-2, Sulphate forms -2 ions SO₄^-2, Nitrate forms -1 ions NO₃^-1

In their solid state ionic compounds are poor electrical conductors because the ions are not free to move.

In their liquid state ionic compounds are good electrical conductors because the electrically charged ions are free to move.

Most ionic compounds are soluble in water.

When dissolved in solution ionic compounds are good electrical conductors because the electrically charged ions are free to move.

Ionic compounds form giant ionic structures which have high melting points due to the strong electrostatic force between the ions.

State	Electrical Conductivity	Reason
Solid	Poor	Ions are in fixed positions and not free to move.
Liquid (Molten)	Good	Ions are free to move in the liquid.
Dissolved in Solution (Aqueous)	Good	Ions are free to move through solution.