When a metal element reacts with a non-metal element an ionic compound is formed. They have a giant lattice structure with strong ionic bonds. A lot of energy is needed to overcome these bonds.
An ion is an atom or group of atoms with a positive or negative charge. Ions form when atoms lose or gain electrons to obtain a full outer shell:
Metal atoms lose electrons from their outer shell when they form ions:
For elements in groups 1, 2 and 3, the number of electrons lost is the same as the group number.
The outer shell of non-metal atoms gains electrons when they form ions:
For groups 6 and 7, the number of electrons gained is equal to (8 - group number).
Group number | Element | Charge on ions | Symbol of ion |
---|---|---|---|
1 | Na | + | Na+ |
2 | Mg | 2+ | Mg2+ |
3 | Al | 3+ | Al3+ |
6 | O | 2- | O2- |
7 | Cl | - | Cl- |
The numbers of protons, neutrons and electrons in an ion can be calculated from its atomic number, mass number and ionic charge.
Remember that:
Some examples are shown in the table below:
Ion name | Ion symbol | Atomic number | Mass number | Protons | Neutrons | Electrons |
---|---|---|---|---|---|---|
Aluminium | Al3+ | 13 | 27 | 13 | 14 | 10 |
Calcium | Ca2+ | 20 | 40 | 20 | 20 | 18 |
Sulfide | S2- | 16 | 32 | 16 | 16 | 18 |