Common Ions (Edexcel IGCSE Chemistry: Double Science)

How to deduce the charge of an ion

• Find the number of electrons in the outer electron shell
• Find out if it is easier for the atom to gain electron or to donate electron (in most cases atoms that have fewer than four electrons, donate electrons and atoms that have more than 4 electrons, receive electrons)
• Atoms that gain electrons become negative ions and atoms that donate electron forms positive ion
• You also need to learn the formula of compound ions, that is, ions made from more than one element

Common ions with a positive charge

Ion	Charge / formula
Group 1 metals	1+ (E.g. Na+)
Group 2 metals	2+ (E.g. Mg2+)
Group 3 metals	3+ (E.g. Al3+)
Silver	Ag+
Copper(II)	Cu2+
Iron(II)	Fe2+
Iron(III)	Fe3+
Lead(II)	Pb2+
Zinc(II)	Zn2+
Hydrogen	H+
Ammonium	NH4+

Common ions with a negative charge

Ion	Charge / formula
Group 5 non- metals	3- (E.g. N3-)
Group 6 non- metals	2- (E.g. O2-)
Group 7 non- metals	1- (E.g. Cl-)
Hydroxide	OH-
Carbonate	CO32-
Nitrate	NO3-
Sulfate	SO42-