Also, here's a mnemonic that's worth remembering (at least for me). These are the diatomic elements (they form in pairs of two).
Have - H - Hydrogen
No - N - Nitrogen
Fear - F - Fluorine
Of - O - Oxygen
Ice - I - Iodine
Cold - Cl - Chlorine
Beer - Br - Bromine
I know, it's kinda stupid, but it helped me...