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Ions are electrically charged particles formed when atoms [atoms: An atom is the smallest part of an element that still has the properties of that element, comprising electrons surrounding a nucleus of protons and neutrons. ] lose or gain electrons [electrons: Sub-atomic particles, with a negative charge and a negligible mass relative to protons and neutrons. ]. They have the same electronic structures as noble gases.
Metal atoms form positive ions, while non-metal atoms form negative ions. The strong electrostatic [electrostatic: An electrostatic force is generated by differences in electric charge (ie positive and negative) between two particles. It can also refer to electricity at rest. ] forces of attraction between oppositely charged ions are called ionic bonds.
Ionic compounds [ionic compound: An ionic compound occurs when a negative ion (an atom that has gained an electron) joins with a positive ion (an atom that has lost an electron). The ions swap electrons to achieve a full outer shell. ] have high melting and boiling points.
How ions form
Ions are electrically charged particles formed when atoms lose or gain electrons [electrons: Sub-atomic particles, with a negative charge and a negligible mass relative to protons and neutrons. ]. This loss or gain leaves a complete highest energy level, so the electronic structure of an ion is the same as that of a noble gas - such as a helium, neon or argon.
Metal atoms and non-metal atoms go in opposite directions when they ionise:
- Metal atoms lose the electron, or electrons, in their highest energy level and become positively charged ions.
- Non-metal atoms gain an electron, or electrons, from another atom to become negatively charged ions.
Positively charged sodium and aluminium ions
Negatively charged oxide and chloride ions
How many charges?
There is a quick way to work out what the charge on an ion should be:
- the number of charges on an ion formed by a metal is equal to the group number of the metal
- the number of charges on an ion formed by a non-metal is equal to the group number minus eight
- hydrogen forms H+ ions
| Group 1 | Group 2 | Group 3 | Group 4 | Group 5 | Group 6 | Group 7 | Group 0 | |
|---|---|---|---|---|---|---|---|---|
| Example element | Na | Mg | Al | C | N | O | Cl | He |
| Charge | 1+ | 2+ | 3+ | Note 1 | 3- | 2- | 1- | Note 2 |
| Symbol of ion | Na+ | Mg2+ | Al3+ | Note 1 | N3- | O2- | Cl- | Note 2 |
Note 1: carbon and silicon in Group 4 usually form covalent bonds [covalent bonds: A covalent bond between atoms forms when atoms share electrons to achieve a full outer shell of electrons. ] by sharing electrons.
Note 2: the elements in Group 0 do not react with other elements to form ions.
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