Question

What are the rules for writing a formula of a compound?

Answer 1

The rules for writing a chemical formula are as follows:

1. Write the symbol of the element / ion which combine to form molecule of the compound.
2. If a compound contains a metal and non-metal, the symbol of metal is written first followed by that of non-metal.
3. Balance the charge/valency on an ion.
4. Polyatomic ion must be written in bracket.
5. If polyatomic ion is one then bracket is not required.

Example:

How to write chemical formula of water?

1. Water is contains the element of hydrogen and oxygen.

Firstly, we will write symbols of hydrogen and oxygen.

H O

1. Write the valency of each element.

H O

1 2

1. Write the valencies of the element as subscript by interchanging.

H₂ O₁

1. The formula of water is written as H₂O.