Chemical Formula of Ionic Compounds

Formula of Ions

  1. Ionic compounds made up of positive ions and negative ions.
  2. To write the formula of an ionic compound, we need to know the symbol and charge of the ions in the compound.

Positive ions that you need to know in SPM form 4 chemistry:

Ion
Symbol
Ion
Symbol
Potassium
K+
Calcium
Ca2+
Sodium
Na+
Magnesium
Mg2+
Lithium
Li+
Zinc
Zn2+
Hydrogen
H+
Barium
Ba2+
Argentums(I)
Ag+
Iron (II)
Fe2+
Mercury(I)
Hg+
Tin (II)
Sn2+
Ammonium
NH4+
Lead(II)
Pb2+
AluminiumAl3+Copper(II)
Cu2+
Iron (III)Fe3+Manganese(II)
Mn2+
Negative ions that you need to know in SPM form 4 Chemistry
Sulphate
Carbonate
Nitrate
Hydroxide
SO42-
CO32-NO3OH

Fluoride

Chloride
Bromide
Iodide
Oxide
F
Cl
Br
I
O2-

Negative ions that you need to know in SPM form 5 Chemistry

PhosphatePO43-
EthanoatCH3COO
Manganate(VII)MnO4
Dichromate(VI)Cr2O72-
ThiosulphateS2O32-

 

Chemical Formlula of Ionic Compounds

2 Requirements to form the formula of an ionic compound
  1. Have at least 2 types of ions that contain opposite charge.
  2. The amount of positive charge/charges must be equal to the amount of negative charge/charges in the compound.
 
Example 1 – If the Charge of the Positive Ions = Charge of Negative Ions Write the formula of each of the following compound
  1. Potassium bromide
  2. Sodium chloride
Answer: a. Potassium bromide
b. Sodium chloride
Example 2 – If the Charge of the Positive Ions ≠ Charge of Negative Ions
Write the formula of each of the following compound
  1. Calcium iodide
  2. Sodium oxide
Answer:
a. Calcium iodide
b. Sodium oxide
Example 3 – If there is more than 1 element in the ion
Write the formula of each of the compound
  1. Ammonium sulphate
  2. Zinc nitrate
Answer: a. Ammonium sulphate
b. Zinc nitrate
Example 4 – Formulae of Acid
Write the formula of the following acid
  1. Hydrochloric acid
  2. Sulphuric acid
  3. Nitric acid
  4. Ethanoic acid
  5. Phosphoric acid
  6. Carbonic acid
Answer: a. Hydrochloric acid
b. Sulphuric acid
c. Nitric acid
d. Ethanoic acid
e. Phosphoric acid
f. Carbonic acid

Formula of Molecule

In SPM, you need to know the formulae of the following molecules

Fluorine
 F2
Hydrogen chloride
 HCl
Chlorine
 Cl2
Hydrogen bromide
 HBr
Bromine
 Br2
Hydrogen iodide
 HI
Iodine
 I2
Nitric oxide
 NO
Carbon dioxide
 CO2
Nitrogen dioxide
 NO2
water
 H2O
Nitrous oxide
 N2O
Ammonia
 NH3
Tetrachloromethane
 CCl4
Sulphur trioxide
 SO3
Hydrogen sulphide
 H2F
Sulphur dioxide
 SO2
Glucose
 C6H12O62