Redox

Oxidation is loss (of electrons) Reduction is gain (of electrons)

Lose electrons and are oxidised themselves

Calcium is being oxidised as it is losing electrons Oxygen is being reduced as it is gaining electrons Ca = reducing agent 1/2 O2 = oxidising agent

Gain electrons and are reduced themselves

Oxidation number always O E.x. cl2, O2

Number is same as charge on ion E.g. Cl- = -1 Ca2+ = +2

Always +1 E.x. KCl

Always +2 E.x. CaO

Always +3 E.x. Al2O3

+1 (except in hydrides where it is -1) E.x. HF Hydride ex: NaH

Always -1 E.x. KF

• 2 (except in peroxides where -1 and +2 in OF2) e. g. Li2O O has value of -1 in H2O2

All the oxidation states must add to overall charge of molecule O= (-2x4) = -8 -8 -> -2 = 6 so, +6

Variable oxidation states

Represented with Roman numeral E.g. Charge of +3 = Iron (III) oxide

As chlorine is bonded to oxygen, add -ate to the end Chlorate (III)

Decrease in oxidation number

Increase in oxidation number

Oxidised and form salt and hydrogen gas

-1 unless with fluorine, becomes +