Atoms of some elements do not go out alone. "I Bring Clay From Our New House" is a mnemonic device to help you remember which elements are diatomic. As a rule, the diatomic elements travel in the company of one or more other atoms. The word, diatomic, means, of course, two atoms. The idea is that atoms of these elements find another atom to bond to. Nitrogen, for example, bonds to oxygen in many different ratios. In their elemental form, however (that means, for example, as pure nitrogen) they bond together in pairs. You don’t often find nitrogen atoms, N. You usually find nitrogen molecules, N2. Likewise for I2, Br2, Cl2, F2, O2 and H2. Hence the term diatomic. For the record, elemental phosphorus is tetratomic (P4) and elemental sulfur is octatomic (S8). If you wish to remember these, just add "for (4) Paving 8 Sidewalks" to the sentence above. Sorry about the Americanism, but footpath doesn’t start with s. Suggestions are welcome.