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:
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.