Question

Why do oxidation numbers relate to valence electrons?

Answer 1

Because, formally, oxidation numbers relate to the loss or gain of valence electrons.

Explanation:

Let us take a simple oxidation reaction:

`C(s) + O_2(g) rarr CO_2(g)`

Now the oxidation numbers of the elements, dioxygen and carbon, are quite properly regarded as `"ZERO"`. They have neither donated nor accepted electrons. But in the reaction, the dioxygen oxidant is conceived to have accepted 4 electrons, and the carbon reductant is conceived to have donated 4 electrons. This is quite clear from the oxidation numbers of the elements in `CO_2`, which feature `C(+IV)` and `O(-II)` as formal oxidation states.

The same redox transfer can also be invoked for dihydrogen combustion:

`H_2(g) +1/2O_2(g) rarr H_2O(g)`

How do electrons transfer here?