Transition Metal Chemistry

1. Transition Metal Chemistry The Chemistry of the d-block elements

2. The Periodic Table p s d

3. Electronic configurations Using the aufbau principle: 1s2,2s2, 2p6,3s2, 3p6,4s2, 3d1 1s2,2s2, 2p6,3s2, 3p6,4s2, 3d10 1s2,2s2, 2p6,3s2, 3p6,4s2, 3d6

4. The two exceptions You would expect Chromium to have the electronic configuration: 1s2,2s2, 2p6,3s2, 3p6,4s2, 3d4 But in fact it has the configuration:1s2,2s2, 2p6,3s2, 3p6,4s1, 3d5 There is a special stability associated with half-filled and full sub-shells. Copper: 1s2,2s2, 2p6,3s2, 3p6,4s1, 3d10

5. Ions • Transition metals are defined as metallic elements with an incomplete d sub-shell in at least one of their ions. • Form positive (+) ions by losing electrons. • These electrons come from the 4s sub-shell first, then from the 3d sub-shell: Fe atom: 1s2,2s2, 2p6,3s2, 3p6,4s2, 3d6 Fe2+ ion: 1s2,2s2, 2p6,3s2, 3p6, 3d6

6. Complex Ions and Complexes Understanding Transition metal compounds

7. In aqueous solution • Transition metal ions exist as complex ions in aqueous solution, e.g. Co(H2O)62+ What shape is this?

9. Ligands Formed through donation of electron pairs Coordinate covalent bond The water molecules are an example of ligands LIGAND: molecules or anions which attach to the metal atom in a complex via coordinate (dative) covalent bonds Number of bonds formed with ligands = COORDINATION NUMBER Assemble is known as a COMPLEX ION So instead of existing in solution as free ions, e.g. Cu2+, exist as complex ions, Cu(H2O)52+

10. Shapes of complex ions

11. Naming ligands

12. Categories of ligand • MONODENTATE LIGAND: the ligand bonds to the metal using one atom • POLYDENTATE LIGANDS: the ligand bonds to the metal using more than one atom

14. Common Examples Chlorophyll Haemoglobin

15. Determining coordination number Number of bonds formed with ligands = COORDINATION NUMBER 6 is the most common coordination number

16. Forming a complex • The cation or anion cannot exist on their own and must have their charges balanced • The complex ion will bond with oppositely charged ions to form a complex

17. Naming Coordination Compounds • Cation precedes anion • Complex ion names are one word: ligands first, then metal • Ligands will have a Greek prefix in front • If the complex ion is an anion, it ends in -ate • The metal name is followed by the oxidation state in Roman Numerals

18. Old vs New • CuSO4·5H2O vs [Cu(H2O)5SO4] • Copper(II) sulphate pentahydrate • Pentaaquacuprum(II) sulphate

19. Colour in Transition Metal Compounds

20. Why coloured? Transition metal ions are often coloured They absorb EM radiation because of loss of degeneracy of d-orbitals Those which absorb in the visible region will appear the complementary colour

21. The 5 d-orbitals in an isolated atom are degenerate • Ligands cause the d-orbitals to become non-degenerate • Different ligands cause different splitting effects

22. Crystal field splitting (energy), Δ

23. In an octahedral complex, the ligands lie on the x, y and z axis Their electrons have a greater repulsive effect on the d-orbitals which lie on the same axis

24. Spectrochemical Series • An arrangement of ligands according to the relative magnitudes of the crystal field splittings they induce in the d-orbitals of a metal ion • I-< Br-< Cl- < F- < OH- < H2O < NH3 < NO2- < CN- < CO Weak-bonding ligands Strong-bonding ligands Increasing Δ Therefore, different ligands will result in different colours

25. Gemstones Cr3+ in Al2O3 Cr3+ in Be3Al2(SiO3)6

26. Catalysis Transition metals as catalysts

27. Catalysts provide an alternative pathway with a lower activation energy • Transition metals can use half-filled or empty orbitals to form intermediate complexes (e.g. 4p) • They can change oxidation state during a reaction, then revert back to their original state