Some of these are found straight from the periodic table, but some of them it is just easier to memorize.
Oxygen is gaseous form is [tex] O_{2} [/tex].
Gold is Au.
Iron is Fe.
Oxygen atom is O, because we are not talking about it in the gaseous state.
Sulfur is S.
Calcium is Ca.
Lead is Pb.
Nitrogen gas is [tex] N_{2} [/tex], for the same reason as oxygen gas.
Nitrogen atom is N, for the same reason as oxygen atom.
