Transition Metal Chemistry

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Transition Metal Chemistry

• The Chemistry of the d-block elements

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The Periodic Table
p
s
d
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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
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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
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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
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Complex Ions and Complexes

• Understanding Transition metal compounds

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In aqueous solution

• Transition metal ions exist as complex ions in
  aqueous solution, e.g.

Co(H2O)62
What shape is this?
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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
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Shapes of complex ions
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Naming ligands
Ligand Name
Bromide Carbonate Cyanide Hydroxide Ammonia Carbon monoxide Water Bromo Carbonato Cyano Hydroxo Ammine Carbonyl Aqua
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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

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Common Examples
Chlorophyll
Haemoglobin
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Determining coordination number
Number of bonds formed with ligands
COORDINATION NUMBER
Complex ion Coordination number
Ag(NH3)2 HgI3- W(CO)64 2 3 6
6 is the most common coordination number
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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 Cation Anion
Pt(NH3)6Cl4 Pt(NH3)4Cl2Cl2 K4Fe(CN)6 Pt(NH3)64 Pt(NH3)4Cl22 K Cl- Cl- Fe(CN)64-
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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

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Old vs New

• CuSO45H2O vs Cu(H2O)5SO4
• Copper(II) sulphate pentahydrate
• Pentaaquacuprum(II) sulphate

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Colour in Transition Metal Compounds
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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
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• 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

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Crystal field splitting (energy), ?
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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
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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-lt Br-lt Cl- lt F- lt OH- lt H2O lt NH3 lt NO2- lt CN-
  lt CO

Weak-bonding ligands
Strong-bonding ligands
Increasing ?
Therefore, different ligands will result in
different colours
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Gemstones
Cr3 in Al2O3
Cr3 in Be3Al2(SiO3)6
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Catalysis

• Transition metals as catalysts

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• 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