Can someone summarise how to assign OXIDATION NUMBERS in a nutshell!

[blipblopify]

So I've practically gotten all the oxidation number questions on the trial exams wrong, can someone please teach me how to figure out how to sieve through an oxidation number question?

[ligands]

hydrogen = +1
oxygen = -2
when balancing equations use h2o to balance oxygen's, h+ to balance hydrogen's and electrons to balance charge

[Somye]

A really easy way to identify if you have a redox equation in a multi choice question is by checking if any result/ start off with a pure elemental substance, as the oxidation numbers of it will have change/will change


So, you can take a molecules overall charge to be the resulting number from the atoms that make it up. For example, Cl- has a charge of -1, therefore its oxidation number is -1

Oxygen is always -2 (except in peroxides), and H can either be + or - 1.

That's the basis for most of your knowledge of oxidation numbers, the rest can be derived from that


eg. PO4 3-, what is the oxidation number of phosphorous
we know that O is -2, and the sum of oxidation numbers = -3. So let's assign the oxidation number of P as x
So, x + 4(-2) = -3, therefore x = +5, and that's the oxidation number

You'll get better with practice, so that most of that goes on in your head

[Starlight]

Straight from my chem lecture (I do vce chem in uni)

Elements
Elemental atoms    0

Compounds
Group 1 (I)   +1
 Group 2 (II)   +2
Group 13 (III)  +3
Group 14 (IV)  +4 (except C,Si)
Hydrogen +1 with non-metals -1 with metals
Fluorine -1
 Oxygen -2 except with F, -1 in peroxides


The oxidation number of a monoatomic atom is the same as its charge, e.g. Na+ has oxidation number of +1

The sum of the oxidation numbers must be zero for a neutral molecule.

The sum of the oxidation numbers must be equal to the overall charge for a molecular ion such as SO42-