oxidation and reduction / redox

R3.2.1

oxidation state/number

• charge the atom would have if the compound were composed of ions

• measure how electrons are distributed

• increase in oxidation state means the atom has lost electron control and is oxidised

• decrease in oxidisation state means the atom has gained electron control and has been reduced

oxidation is…

• loss of electrons

• gain of oxygen

• loss of hydrogen

• increase in oxidations tate(more positive)

electronegativity

an atoms strenth/willingness to hold electrons close to it

rules for assigning oxidation state

• free/uncombined electons have 0 as their oxidation state

• in simple ions the individual atoms charge is the same as when they are ions(look at periodic table)

• the sum of oxidations tates in a compound sum up to =0

• the sum of oxidation states in a polyatomic ion =the charge of the ion

• F has -1 in all compounds because it’s the most electromagnetic element

• oxygen always has -2 except when in peroxides(eg. H2O2) where it has -1 or when its bonded to F where it’s +2

• Cl has -1 except when bonded to more electronegative elements like O or F

• H has +1 except with ionic hydrides which G1 and G2 where it’s -1 eg. NaH

• oxidation states of transition metals in a complexion can be worked out from the charge on ligans.

oxyanions

negatively charged ions that contain a central atom bonded to oxygens, thus their name is based on the oxidation state of the cetral atom(usually a non-metal).

eg. 1. NO₃^- has N=5 O=-2 so nitrate(V) not nitrite

2. H₃PO₄ H=+1 P=+5 O=-2 so Phospheric(V) acid

disproportionation reaction

when the same element/atoms is oxidised and reduced

reduction is…

• loss of oxygen

• gain of hydrogen

• gain of electrons

• decrease in oxidation state