The formulae for most elements is just their symbol, but there are some non-metal elements that exist as molecules that contain two atoms joined together. The formulae of these elements are the element's symbol followed by a subscripted '2'. 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.