An ionic compound is made up of charged particles, called ions. It has a giant lattice structure with strong electrostatic forces of attraction.
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 shells of non-metal atoms gain electrons when they form ions:
For elements in groups 6 and 7, the charge on the ion is equal to (8 minus group number).
Group | Element | Ion charge | Ion symbol |
---|---|---|---|
1 | Na | + | Na+ |
2 | Mg | 2+ | Mg2+ |
6 | O | 2- | O2- |
7 | Cl | - | Cl- |
Sulfur is in group 6 of the periodic table. What is the charge on its ions, and is the charge positive or negative?
The charge is negative, since sulfur is a non-metal. The charge on the ion is (8 - 6) = 2.
Iodine is in group 7. What is the charge on its ions, and is the charge positive or negative?
The charge is negative, since iodine is a non-metal. The charge on the ion is (8 - 7) = 1.