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Ionic compounds - EdexcelNames and formulae of ionic compounds

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.

Part of Chemistry (Single Science)Key concepts in chemistry

Names and formulae of ionic compounds

To deduce the formulae of , the formulae of their can be used.

The table shows the names and formulae of some common ions.

CationsAnions
Lithium, Li+Chloride, Cl-
Sodium, Na+Bromide, Br-
Potassium, K+Iodide, I-
Silver(I), Ag+Oxide, O2-
Barium, Ba2+
Calcium, Ca2+
Copper(II), Cu2+
Iron(II), Fe2+
Lead(II), Pb2+
Magnesium, Mg2+
Zinc, Zn2+
Aluminium, Al3+
Iron(III), Fe3+
CationsLithium, Li+
AnionsChloride, Cl-
CationsSodium, Na+
AnionsBromide, Br-
CationsPotassium, K+
AnionsIodide, I-
CationsSilver(I), Ag+
AnionsOxide, O2-
CationsBarium, Ba2+
CationsCalcium, Ca2+
CationsCopper(II), Cu2+
CationsIron(II), Fe2+
CationsLead(II), Pb2+
CationsMagnesium, Mg2+
CationsZinc, Zn2+
CationsAluminium, Al3+
CationsIron(III), Fe3+

Working out a formula

The formula for an ionic compound must contain the same number of positive and negative so that the charges are balanced and it is neutral overall. Here are some examples.

Example 1

Sodium chloride contains Na+ and Cl- ions:

  • this is one positive charge and one negative charge
  • the charges are balanced
  • so the formula is NaCl

Example 2

Magnesium oxide contains Mg2+ and O2- ions:

  • this is two positive charges and two negative charges
  • the charges are balanced
  • so the formula is MgO

Example 3

Aluminium oxide contains Al3+ and O2- ions:

  • this is three positive charges and two negative charges
  • to balance, we need two Al3+ ions and three O2- ions
  • so the formula is Al2O3
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Polyatomic ions
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Properties of ionic compounds

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