Chemical symbols and formulae

Chemical symbols

Each element is represented by its own chemical symbol. A chemical symbol:

  • consists of one or two letters
  • always starts with a capital letter, with any other letter in lower case

For example, the element mercury is shown as Hg. It must not be shown as HG, hg or hG.

The periodic table shows the names and symbols of the elements.

Periodic table with Metals coloured in red and Non-metals coloured in yellow.Each box in the periodic table contains the chemical symbol for an element

Chemical formulae of elements

A chemical formula is used to represent an element or compound in balanced chemical equations.

The formulae for most elements is just their symbol, but some non-metal elements exist as molecules that contain two atoms joined together. These molecules are called diatomic molecules. To show this, their formulae all have a subscript number 2 in them. For example:

  • iodine, I2
  • bromine, Br2
  • chlorine, Cl2
  • fluorine, F2
  • oxygen, O2
  • nitrogen, N2
  • hydrogen, H2

A mnemonic can be used to remember these elements:

IBring Clay For Our New House.

It’s important to recognise which elements are written with a subscript 2 and which are not. Take care to use the correct form in chemical equations involving these elements.