variable oxidation states
DESCRIPTION
Variable Oxidation States. Objectives. Be able to... Determine whether elements have been oxidised or reduced in chemical reactions Confidently use half equations to describe redox reactions - PowerPoint PPT PresentationTRANSCRIPT
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