Question

Why is the number of valence electrons associated with the oxidation number of the element?

Answer 1

Why, because we conceive of the oxidation number as the number of electrons GAINED or RECEIVED by an atom upon chemical reaction.

Explanation:

And oxygen, which as an element has a high nuclear charge (i.e. it comes to the right of the Periodic Table as we face it), tends to accept electrons.........

Guidelines for assigning oxidation numbers are as follows......

`1.` `"The oxidation number of a free element is always 0."`

`2.` `"The oxidation number of a mono-atomic ion is equal"` `"to the charge of the ion."`

`3.` `"For a given bond, X-Y, the bond is split to give "X^+` `"and"` `Y^-`, `"where Y is more electronegative than X."`

`4.` `"The oxidation number of H is +1, but it is -1 in when"` `"combined with less electronegative elements."`

`5.` `"The oxidation number of O in its"` compounds `"is usually -2, but it is -1 in peroxides."`

`6.` `"The oxidation number of a Group 1 element"` `"in a compound is +1."`

`7.` `"The oxidation number of a Group 2 element in"` `"a compound is +2."`

`8.` `"The oxidation number of a Group 17 element in a binary compound"` `"is -1."`

`9.` `"The sum of the oxidation numbers of all of the atoms"` `"in a neutral compound is 0."`

`10.` `"The sum of the oxidation numbers in a polyatomic ion"` `"is equal to the charge of the ion."`

And so when elemental oxygen reacts with say carbon, we conceive that the 2 oxygen atoms accept 2 electrons, and that carbon atom donates two electrons...............

`stackrel(0)C(s)+stackrel(0)O_2(g)rarrstackrel(-II)O=stackrel(+IV)C=stackrel(-II)O(g)`

As always the sum of the oxidation numbers of the elements in a compound or ion, is equal to the charge of the compound or ion, and here the `CO_2` product is neutral.