hoe to write chemical formulae for simple compounds?

Hi Lekhashree!

 

The chemical formula of any compound can be obtained from the valencies of the constituting elements. To write the chemical formula of a compound, one should have prior knowledge of two things:

1.  The symbols of the constituent elements, and

2.  The combining capacity of each atom constituting the compound

For example, both hydrogen and chlorine have a valency of 1. Therefore, one atom of hydrogen reacts with one atom of chlorine to form one molecule of hydrogen chloride.

While writing the chemical formula, certain rules need to be kept in mind. These rules are given below:

  1.  The valencies or charges on the ions must be balanced.

  2.  In case of a compound consisting of a metal and a non-metal, the symbol of the metal is written first. For example, in calcium chloride (CaCl₂) and zinc sulphide (ZnS), calcium and zinc are metals, so they are written first, whereas chlorine and sulphur are non-metals.

Thus, the formula of aluminium sulphate is Al₂(SO₄)₃. Brackets are used when we have two or more of the same ions in a formula. Here, the bracket with a subscript 3 indicates that three sulphate groups are joined to two aluminium atoms.

Hope, this is clear now. I would suggest you to practice writing formulas for atleast 2o compounds. Gradually, you will achieve confidence doing it.

Do write back to us if you face any difficulty.

Best wishes!