oxidation states

oxidation number

the equivalent charge of a species compared to its atomic state

elements uncombined

e.g Na, Zn, Mg

0

a neutral compound

e.g H2, CO2

must add up to 0

an ion

e.g SO2-4, Na+

must add up to the charge of the ion

fluorine

-1

oxygen

-2 (except fluorine or peroxides[-1])

hydrogen as ions (with non metals)

+1

hydrogen with metals (hydrides)

-1

group 1

+1

group 2

+2

aluminium

+3

reduction

reducing ability

reducing agent

reduction: gain of electrons (decrease in oxidation number)

reducing ability: how easily a species loses electrons (to reduce other species)

reducing agent: the species that donates electrons (is oxidised)

oxidation

oxidation: loss of electrons (increase in oxidation number)

oxidising ability: how easily a species gains electrons (to oxidise other species)

oxidising agents: species that gain electrons (are reduced)

metals usually…

metals usually form positive ions by loss of electrons with an increase in oxidation number

non metals usually…

form negative ions by the gain of electrons with a decrease in oxidation number