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Variable Oxidation States

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

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Variable Oxidation States

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  1. Variable Oxidation States

  2. Objectives Be 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

  3. Specification...Where this comes from...

  4. HALF REACTIONS Write both half reactions for the following reaction: Cu + AgNO3 Cu(NO3)2 + Ag Reduction: Ag+ Ag Ag+ + 1e- Ag Oxidation: Cu  Cu+2 Cu  Cu+2 +2e- Cu -2e-  Cu+2

  5. HALF REACTIONS Write both half reactions for the following reaction: HNO3 + I2  HIO3 + NO2 Reduction: N+5 N+4 N+5 + 1e- N+4 Oxidation: I20 I+5 I20 2I+5 +10e- I20 -10e-  2I+5

  6. Half Reactions Write both half reactions for the following reaction: Sn + 2AgNO3  Sn(NO3)2 + 2Ag Reduction: Ag+1 Ag0 Ag+1 + 1e- Ag0 Oxidation: Sn0 Sn+2 Sn0 Sn+2 +2e- Sn0 -2e-  Sn+2

  7. Use the changes in oxidation numbers to identify which atoms are oxidized, and which atoms are reduced: • 2H2 (g) + O2 (g)  2H2O (l) • 2KNO3 (s)  2KNO2 (s) + O2 (g) • NH4NO3 (s)  N2 (g) + 2H2O (g) • (HINT: consider each N separately) • PbO2 (aq) + 4HI (aq)  I2 (aq) + PbI2 (s) + 2H2O (l)

  8. And some more...

  9. Variable Oxidation States • One of the most striking properties • variable oxidation states • The 3d and 4s electrons are •  insimilarenergy levels • availablefor bonding

  10. Variable Oxidation States • Elements of the first transition series • form ions of roughly the same stability by losingdifferentnumbersofthe 3d and 4s electrons

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

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

  13. 1. Scandium and zinc do not exhibit variable oxidation states • Scandiumof 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

  14. 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

  15. 3. Manganese has the highest oxidation state +7 E.g. MnO4-, Mn2O7 Mn7+ ions do not exist.

  16. 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

  17. Draw the structure of Mn2O7

  18. Home Learning • Complete worksheet on Redox and Oxidation States

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