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What is an ion?

What is an ion?

A chemical ion is a charged particle. For example the magnesium ion, Mg2+ and the oxide ion, O2-have respective charges of 2+ and 2-

Other common examples of charged particles are the sodium ion, Na+ and the chloride ion, Cl-

Metals produce positve ions. eg. magnesium ion, Mg2+

Non-metals produce negative ions. eg. oxide ion, O2-

The charge of many ions is related to their position in the periodic table. See the table below.

Group I metals produce ions of a charge of +1. 

Group II metals produce ions of a charge of +2 and so on.

Charges of metallic and non-metallic ions

+1 +2 +3 -3 -2 -1
Lithium, Li+ Beryllium, Be2+ Nitride, N3- Oxide, O2- Fluoride, F-
Sodium, Na+ Barium, Ba2+ Aluminum, Al3+ Phosphide, P3- Sulfide, S2- Chloride, Cl-
Potassium, K+ Calcium, Ca2+ Bromide, Br-

Ions can be divided into two groups based upon their charges.

An cation is a positively charged ion. Metallic elements produce positive ions. Examples of cations include potassium, K+ and calium, Ca2+

An anion is a negatively charged ion. Non-metallic elements produce negative ions. Examples of anions include oxide, O2- and nitride, N3-

The charges are due to a shortage or excess number of electrons in an atom.

Metallic elements have a tendecy to lose electrons in their valence or outer shell and produce postive ions. Metal atoms have either 1, 2 or 3 electrons in their valence shell which are lost in a chemical reaction.

The sodium atom loses one electron producing a positive sodium ion.

Na → Na+ + e

Non metallic elements have a tendecy to gain electrons in their valence or outer shell and produce negative ions. Non metallic atoms have either 5, 6 or 7 electrons in their valence shell. They gain electrons in a chemical reaction.

A chlorine atom gains one electron producing a negative chlorine ion.

Cl + e → Cl