Question

Describe in terms of the number of electrons gained, lost or shared how i) a carbon atom combines with other atoms? ii) a magnesium atom combies with other atoms?

Answer 1

Well, carbon has a large redox manifold and can assume oxidation states of `C(-IV)` thru to `C(+IV)`...

Explanation:

And let us look at some simple oxidation reactions...the carbon oxidation numbers are SUPERSCRIPTED....

`stackrel(-IV)CH_4+2H_2Orarrstackrel(+IV)CO_2+8H^+ +8e^(-)`

And dioxygen gas is of course the OXIDANT...

`1/2O_2 + 2H^+ + 2e^(-) rarr H_2O`...

We take one of the former and FOUR of the latter and add them...

`CH_4+2O_2 + 8H^+ + 8e^(-)+2H_2OrarrCO_2+8H^+ +8e^(-)+4H_2O`

...to give after cancellation...

`CH_4+2O_2 rarrCO_2+2H_2O`

Of course, to represent hydrocarbon combustion we would normally balance the carbons as carbon dioxide, and the hydrogens as water, and add in the required dioxygen.

As required...

And magnesium is commonly oxidized to `Mg(II+)`:

`Mg rarr Mg^(2+) + 2e^(-)`

`1/2O_2+2e^(-) rarr O^(2-)`

...we add these 1:1 to get...

`Mg(s) + 1/2O_2(g) rarr MgO(s)`...