Variable Oxidation States

ObjectivesBe able to...•Determine whether elements have been

oxidised or reduced in chemical reactions•Confidently use half equations to describe

redox reactions•Describe how D-block elements can form

a variety of oxidation states producing compounds of different colours

Specification...Where this comes from...

HALF REACTIONS

Cu + AgNO3 Cu(NO3)2 + Ag

Reduction:

Write both half reactions for the following reaction:

Oxidation:

Ag+ Ag

Cu Cu+2 + 2e-

Cu Cu+2

Ag+ + 1e- Ag

Cu - 2e- Cu+2

HALF REACTIONS

HNO3 + I2 HIO3 + NO2

Reduction:

Write both half reactions for the following reaction:

Oxidation:

N+5 N+4

I20 2I+5 + 10e-

I20 I+5

N+5 + 1e- N+4

I20 - 10e- 2I+5

Sn + 2AgNO3 Sn(NO3)2 + 2Ag

Reduction:

Write both half reactions for the following reaction:

Oxidation:

Ag+1 Ag0

Sn0 Sn+2 + 2e-

Sn0 Sn+2

Ag+1 + 1e- Ag0

Sn0 - 2e- Sn+2

Half Reactions

•Use the changes in oxidation numbers to identify which atoms are oxidized, and which atoms are reduced:1. 2H2 (g) + O2 (g) 2H2O (l)2. 2KNO3 (s) 2KNO2 (s) + O2 (g)3. NH4NO3 (s) N2 (g) + 2H2O (g)

(HINT: consider each N separately)

4. PbO2 (aq) + 4HI (aq) I2 (aq) + PbI2 (s) + 2H2O (l)

And some more...

• One of the most striking properties

variable oxidation states

Variable Oxidation States

• The 3d and 4s electrons are

in similar energy levels

available for bonding

• Elements of the first transition series

form ions of roughly the same stability by losing different numbers of the 3d and 4s electrons

Variable Oxidation States

Oxidation states

Oxides / Chloride

+1Cu2O

Cu2Cl2

+2

TiO VO CrO MnO FeO CoO NiOCuO ZnO

TiCl2 VCl2 CrCl2 MnCl2 FeCl2 CoCl2 NiCl2CuCl2 ZnCl2

+3

Sc2O3 Ti2O3 V2O3 Cr2O3 Mn2O3 Fe2O3 Ni2O3 •

xH2O

ScCl3 TiCl3 VCl3 CrCl3 MnCl3 FeCl3

+4TiO2 VO2 MnO2

TiCl4 VCl4 CrCl4

+5 V2O5

+6 CrO3

+7 Mn2O7

Oxidation states of the elements of the first transition series in their oxides and chlorides

Oxidation states of the elements of the first transition series in their compounds

Element Possible oxidation state

Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn

Element Possible oxidation state

Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn

+3

+1 +2 +3 +4

+1 +2 +3 +4 +5

+1 +2 +3 +4 +5+6

+1 +2 +3 +4 +5+6 +7

+1 +2 +3 +4 +5+6

+1 +2 +3 +4 +5

+1 +2 +3 +4 +5

+1 +2 +3

+2

1. Scandium and zinc do not exhibit variable oxidation states

• Scandium of the oxidation state +3

the stable electronic configuration of argon (i.e. 1s22s22p63s23p6)• Zinc of the oxidation state +2

the stable electronic configuration of [Ar] 3d10

2. (a) All elements of the first transition series (except Sc) can show an oxidation state of +2

(b) All elements of the first transition series (except Zn) can show an oxidation state of +3

3. Manganese has the highest oxidation state +7

E.g. MnO4-, Mn2O7

Mn7+ ions do not exist.

The +7 state of Mn does not mean that all 3d and 4s electrons are removed from Mn to give Mn7+.

Instead, Mn forms covalent bonds with oxygen atoms by making use of its half filled orbitals

Mn

O

OO

O-

Draw the structure of Mn2O7

Mn

O

OO

OMn

O

OO

Home Learning

•Complete worksheet on Redox and Oxidation States