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Transition Metal
Chemistry
The Chemistry of the d-block
elements
The Periodic Table
s
d
p
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
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 subshells.
Copper: 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d10
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
Complex Ions
and Complexes
Understanding Transition metal
compounds
In aqueous solution
• Transition metal ions exist as complex ions in
aqueous solution, e.g.
Co(H2O)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. Cu2+, exist as complex
ions, Cu(H2O)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(NH3)2+
HgI3W(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(NH3)6]Cl4
Cation
Pt(NH3)64+
[Pt(NH3)4Cl2]Cl2 Pt(NH3)4Cl22+
K4[Fe(CN)6]
K+
Anion
ClCl-
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
• CuSO4·5H2O
vs
[Cu(H2O)5SO4]
• 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- < H2O < NH3 <
NO2- < CN- < COIncreasing Δ
Therefore, different ligands will result in different colours
Gemstones
Cr3+ in Al2O3
Cr3+ in Be3Al2(SiO3)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.
4p)
• They can change oxidation state during a
reaction, then revert back to their original state