Transition Metal Chemistry The Chemistry of the dblock

Transition Metal Chemistry The Chemistry of the d-block elements

The Periodic Table s d p

Electronic configurations Using the aufbau principle: 1 s 2, 2 s 2, 2 p 6, 3 s 2, 3 p 6, 4 s 2, 3 d 10 1 s 2, 2 p 6, 3 s 2, 3 p 6, 4 s 2, 3 d 6

The two exceptions You would expect Chromium to have the electronic configuration: 1 s 2, 2 p 6, 3 s 2, 3 p 6, 4 s 2, 3 d 4 But in fact it has the configuration: 1 s 2, 2 p 6, 3 s 2, 3 p 6, 4 s 1, 3 d 5 There is a special stability associated with half-filled and full subshells. Copper: 1 s 2, 2 p 6, 3 s 2, 3 p 6, 4 s 1, 3 d 10

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 4 s sub-shell first, then from the 3 d sub-shell: Fe atom: 1 s 2, 2 p 6, 3 s 2, 3 p 6, 4 s 2, 3 d 6 Fe 2+ ion: 1 s 2, 2 p 6, 3 s 2, 3 p 6, 3 d 6

Complex Ions and Complexes Understanding Transition metal compounds

In aqueous solution • Transition metal ions exist as complex ions in aqueous solution, e. g. Co(H 2 O)62+ What shape is this?

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. Cu 2+, exist as complex ions, Cu(H 2 O)52+

Shapes of complex ions

Naming ligands Ligand Bromide Carbonate Cyanide Hydroxide Ammonia Carbon monoxide Water Name Bromo Carbonato Cyano Hydroxo Ammine Carbonyl Aqua

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

Common Examples Chlorophyll Haemoglobin

Determining coordination number Number of bonds formed with ligands = COORDINATION NUMBER Complex ion Ag(NH 3)2+ Hg. I 3 W(CO)64+ Coordination number 2 3 6 6 is the most common coordination number

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 Complex [Pt(NH 3)6]Cl 4 Cation Pt(NH 3)64+ [Pt(NH 3)4 Cl 2]Cl 2 Pt(NH 3)4 Cl 22+ K 4[Fe(CN)6] K+ Anion Cl. Fe(CN)64 -

Naming Coordination Compounds 1. Cation precedes anion 2. Complex ion names are one word: ligands first, then metal 3. Ligands will have a Greek prefix in front 4. If the complex ion is an anion, it ends in -ate 5. The metal name is followed by the oxidation state in Roman Numerals

Old vs New • Cu. SO 4· 5 H 2 O vs [Cu(H 2 O)5 SO 4] • Copper(II) sulphate pentahydrate • Pentaaquacuprum(II) sulphate

Colour in Transition Metal Compounds

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

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

Crystal field splitting (energy), Δ

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

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 Weak-bonding ligands Strong-bonding ligands • I-< Br-< Cl- < F- < OH- < H 2 O < NH 3 < NO 2 - < CN- < CO Increasing Δ Therefore, different ligands will result in different colours

Gemstones Cr 3+ in Al 2 O 3 Cr 3+ in Be 3 Al 2(Si. O 3)6

Catalysis Transition metals as catalysts

• 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. 4 p) • They can change oxidation state during a reaction, then revert back to their original state