Question

I know that nitrogen, oxygen, etc. are all diatomic. But when do I know to add the 2 at the end of their formula while writing equations?

Answer 1

Always think about the structure of the substance you are looking at.

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• If you write `"H"_2`, it is a bonded molecule, `"H"-"H"`. If you write `2"H"`, you have two NOT-bonded, separate, `"H"` atoms.
• If you write `"N"_2`, it is a bonded molecule, `:"N"-="N":`. If you write `2"N"`, you have two NOT-bonded, separate, `"N"` atoms.

You must also remember to write the phase. `"N"(g)` is possible, but `"N"(l)` and `"N"(s)` are unheard of in ordinary reaction conditions.