Question

What is the `"oxidation number"` of nitrogen in `"ammonia, ammonium ion, and nitrate ion"`?

Answer 1

We gots `stackrel(-III)N`..........

Explanation:

While oxidation number is a formalism, it is a convenient formalism. For ions and molecules, the SUM of the oxidation numbers ALWAYS equals the charge on the ion.

TO illustrate, let's take `NH_3`, `NH_4^+`, and `NO_3^-`; now hydrogen and oxygen in their compounds typically take oxidation numbers of `+I` and `-II` respectively, and they do here.......

ANd thus for ammonia, `3xx(+I)+stackrel"oxidation number"N=0`. Clearly we gots `stackrel"-III"N`.

And for ammonium, `4xx(+I)+stackrel"oxidation number"N=+1`. Clearly we gots `stackrel"-III"N` again.

But for nitrate ion, oxygen is MORE electronegative than nitrogen, and it gets the electrons, `3xx(-II)+stackrel"oxidation number"N=-1`. Clearly we gots `stackrel"+V"N`.

Capisce?

What about `NO`, `NO_2`, `N_2O_5`, `N_2O_4`?