oxidation states and redox

i cannot describe how to combine half equations soz

what is oxidation (in terms of oxygen and electrons)?

• gain of O₂

• the process of e^- loss

what is reduction (in terms of oxygen and electrons)?

• loss of O₂

• the process of e^- gain

what is an oxidising agent (in terms of oxidation and in terms of electrons)?

• an agent which causes a substance to be oxidised (and so are reduced themselves)

• this makes them e^- acceptors

what is a reducing agent (in terms of reduction and electrons)?

• an agent which causes a substance to be reduced (and so are oxidised themselves)

• this makes them e^- donors

what is a half equation?

an equation showing the loss or gain of e^-

what is an oxidation state?

a +ve/-ve number showing how many e^- an element has lost/gained

what is the oxidation state of an uncombined element?

0

what is the sum of the oxidation states in a compound?

0

what is the sum of the oxidation numbers in an ion?

the charge on the ion

what is the oxidation state of F usually?

-1

what is O’s oxidation state usually? what are the exceptions?

• -2

• except when combined w/ F or in peroxides (compound where 2 O atoms are joined by a single cov bond)

what is the oxidation state of a group I metal always?

+1

what is the oxidation state of a group II metal always?

+2

what is the oxidation state of H usually? what are the exceptions?

• +1

• except when combined w/ group I or II metals

what is the oxidation state of a halide usually? what is the exception?

• -1

• except when combined w/ F or O

what does an increase in oxidation state mean (in terms of oxidation/reduction and e^-)?

• oxidation has occurred

• so e^- have been lost

what does a decrease in oxidation state mean (in terms of oxidation/reduction and e^-)?

• reduction has occurred

• so e^- have been gained

give the 4 steps needed to balance a half equation:

1. balance element changing oxidation state

2. balance using H₂O

3. balance using H⁺

4. balance charge w/ e^-