IB Chemistry – Transition metals
Naming system
Transition metal compounds and complexes are named according to whether the
transition metal forms part of the positive or negative ion. If the metal ion is positive
(usually non-complex) the transition metal name does not change.
e.g.
FeSO4

iron II sulphate
If the transition metal appears as part of a negative ion then the name of the transition
metal changes as follows:
Transition metal
titanium
vanadium
chromium
manganese
iron
cobalt
nickel
copper
e.g.
becomes
name in negative ion
titanate
vanadate
chromate
manganate
ferrate
cobaltate
nickelate
cuprate
[Fe(CN)6]3-  hexacyano ferrate (III)
Properties of the transition metals
Characterised by the following:1.
Variable oxidation state
2.
Coloured compounds
3.
Complex ion formation
4.
Magnetism
5.
Catalysts
6.
Variable coordination numbers (see complex ions)
7.
Cluster compounds (not important for IB except in the Biochemistry section)
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IB Chemistry – Transition metals
Variable oxidation state
We must learn a few of the common oxidation states
Iron
II and III
Manganese
II, IV and VII
Chromium
II, III and VI
Copper
I and II
1.
Give examples of compounds containing each of the oxidation states above
(name and formula)
Coloured complexes
The transition metals are normally colourless if the ion is not surrounded by ligands. If it
is, this creates a crystal field (region of space in which electrostatic forces create an
electrical field) in which the d orbitals have unequal energy and because of this
transitions can occur between them. These transitions require energy provided by light
from the visible portion of the electromagnetic spectrum (this has the correct amount of
energy). Hence the transition metal ions absorb part of the visible spectrum and we see
only those parts of the spectrum which are allowed to pass through.
Example: copper II salts usually appear blue because they absorb light from the red part
of the visible spectrum.
2
For each of the examples of oxidation states in question 1 state the colour of
the compound you have chosen.
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IB Chemistry – Transition metals
The colour depends on the difference in energy between the non-degenerate “d” orbitals
and this difference is created by the crystal field. This, in turn, also depends on the nature
of the ligand surrounding the transition metal ion as this affects both the splitting and the
geometry of the complex ion.
Example:
Copper II sulphate Blue (here the Cu2+ ion is surrounded by six water molecules as
ligands)
Copper II chloride Green (here the Cu2+ ion is surrounded by four Cl- ions as ligands)
3. Find 5 (five) more examples from the literature of changing ligand affecting the
colour of the transition metal ion (there must be no change in oxidation state)
Give the conditions required for each of the examples chosen and state how you
would carry out the change in the lab.
Complex ion formation
The transition metal ions have partially filled ‘d’ orbitals which can accept electron pairs
by dative coordinate bonding. These form complex ions which may be positive or
negative depending on the ligands attached. The shape of the complex ions depends on
the ligands, the oxidation state and type of transition metal involved.
Nomenclature:
The transition metal retains its name when it is involved in a positive ion but changes it in
a negative ion to end with “-ate”.
Example:
[Fe(H2O)6]2+
Hexa aqua iron II
[Fe(CN)6]4-
Hexa cyano ferrate II
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IB Chemistry – Transition metals
Common shapes
6 ligands
4 ligands
2 ligands
octahedral
tetrahedral or square planar
linear
4. Draw and name 2 examples of each of the three geometries of complex above.
Magnetism
This should not be confused with ferromagnetism, which is a very strong effect created
when many magnetic atoms group together into domains increasing the magnetic
behavior. This only happens in the three metals iron, cobalt and nickel of which iron is
the main protagonist. The magnetism described here is paramagnetism which occurs
when an atom or iron has unpaired electrons. These unpaired electrons give the atom a
magnetic field which can be affected by an external magnetic field and hence easily
detected. To decide the number of unpaired electrons is not as straightforward as it would
appear to be from a consideration of the d orbitals as these are usually non-degenerate
having been “split” by the crystal field. In fact the reverse is true in that we usually arrive
at the arrangement of “d” orbitals by a consideration of the magnetic properties.
Example:
Iron 2+ has the configuration 1s2 2s2 2p6 3s2 3p6 4s0 3d6
This would suggest four unpaired electrons in the five d orbitals, however in an
octahedral field the “d” orbitals are split three and two with the dxy dxz dyz havin a lower
energy than the other two.
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IB Chemistry – Transition metals
The electrons fill up these orbitals first and so the compound are not magnetic
(diamagnetism)
Summary: the magnetic properties depend on the geometry of the complex ion and the
ligand strength, as well as the total number of electrons in the d orbitals.
5. Suggest, with reasons, the likely magnetic properties of the following ions. Ñame
them.
a)
[Fe(H2O)6]2+
b)
[Fe(CN)6]3-
c)
[Fe(CN)6]4-
d)
[CoCl4]2-
e)
[Mn(NH3)6]2+
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IB Chemistry – Transition metals
Catalytic properties
6.
Find examples of the use of each of the period 4 transition metals as catalysts.
Note whether they are used as homogeneous or heterogeneous catalysts and
show the industrial process envolved.
page 6