Chapter 15: Transition Metals
15.1 General Properties of Transition Metals
15.2 Complex Formation and the Shape of Complex Ions
15.3 Coloured Ions
15.4 Variable Oxidation States of Transition Elements
15.5 Catalysis
15.1 General Properties of Transition Metals
Learning Objectives:
1. Recall the general properties of transition metals.
2. Explain these properties in terms of electronic structure.
Review: Electron Configuration
• Write out the electron configurations for the Period 4 d-block
elements (Sc to Zn). Use the noble gas abbreviation.
Sc – [Ar] 4s2 3d1
Ti – [Ar] 4s2 3d2
V – [Ar] 4s2 3d3
Cr – [Ar] 4s1 3d5
Mn – [Ar] 4s2 3d5
Fe – [Ar] 4s2 3d6
Co – [Ar] 4s2 3d7
Ni – [Ar] 4s2 3d8
Cu – [Ar] 4s1 3d10
Zn – [Ar] 4s2 3d10
Review: Electronic Configurations of Ions
• Write the electron configurations for the Sc3+, the V2+ and the Cu2+
ions.
• Sc3+
• V2+
• Cu2+
[Ar]
[Ar] 3d3
[Ar] 3d9
Remember:
Always form positive ions.
S-block electrons always lost first.
Transition Metals
Transition Metal = a metal that can form one or more stable ions with a
partially filled d-subshell
Scandium and Zinc are NOT transition metals
• Scandium and Zinc are not considered transition metals, even though
they are d-block metals, because they only form one stable ion Sc3+
and Zn2+ and neither of those ions contains a partially filled d-orbital.
• Sc3+
• Zn2+
[Ar]
[Ar] 3d10
(empty d-subshell)
(full d-subshell)
Physical Properties (Metallic Properties)
• Good conductors of heat and electricity
• Hard
• Strong
• Shiny
• High melting and boiling points
Low Reactivity
• Physical properties and fairly low reactivity makes them very useful
materials.
Examples:
• Iron (and alloy steel) useful as a building material for high strength.
• Copper for water pipes and electrical wires
• Titanium for jet engine parts (withstands high temperatures)
Special chemical properties are caused by
partially filled d-subshells
• Variable Oxidation States – the 4s and 3d energy levels are
very close together, so different amounts of electrons can be
lost using similar amounts of energy
• Coloured – transition metal ions are coloured
• Catalysis – they are good catalysts as can easily go between
two stable ions
• Complex Formation
15.2 Complex formation
Learning Objectives:
1. Describe the formation of complex ions.
2. Determine the shape of complex ions.
3. Draw structure of complex ions.
4. Determine the charge of complex ions.
Formation of Complex Ions
• Complex ion = a metal ion surrounded
by coordinately bonded ligands.
• Coordinate bond (dative covalent
bond) = a covalent bond in which both
electrons in the shared pair come from
the same atom
• Ligand = an ion or molecule that
donates a pair of electrons to a central
metal ion.
Shape of Complex Ion
• Coordination number
determines the shape of a
complex ion.
• Coordination number = the
number of coordinate bonds to
ligands in a complex ion
Transition metal ions
commonly form
octahedral complexes
with small ligands
(H2O, NH3).
Transition metal ions
commonly form
tetrahedral complexes
with larger ligands (Cl-)
This is because fewer
ligands fit around the
central metal ion.
Multidentate ligands
• Ligands that can only form one bond are called unidentate.
• Some ligands can attach to the metal ion more than once.
• These are called multidentate ligands.
• They have multiple lone pairs that can be donated to the metal ion.
• Bidentate ligands = form two coordinate bonds with metal ion
• Tridentate ligands = form three
• Tetradentate ligands = forms four
Oxidation States
• The total oxidation state of the complex ion is placed outside square
brackets (Example: [Cu(H2O)6]2+ has a total charge of 2+).
Total Oxidation State
of Complex Ion
Oxidation State of the
Metal Ion
• What is the charge of the metal ion in [Cu(H2O)6]2+ ?
• +2 = x + 0  x = +2  Cu2+
Sum of Oxidation
States of Ligands
Examples of Complex Ions (that you need to know)
• Cis-platin [Pt(NH3)2Cl2]
• Tollen’s reagent [Ag(NH3)2]+
• Haemoglobin
Cis-platin
• [Pt(NH3)2Cl2]
• Square planar shape
• Cis (The chlorines are on the same
side)
• Successful anti-cancer drug
• Trans-platin interestingly has no
anti-cancer properties.
Tollen’s Reagent
• Contains complex ion [Ag(NH3)2]+
• Linear shape.
• Distinguishes between aldehydes
and ketones.
• Aldehydes reduce ion to Ag (silver
mirror).
Haemaglobin
• Contains a Fe2+ ion which are hexacoordinated (6 coordinate bonds).
• Four coordinate bonds are from
nitrogens on the tetradentate ligand
called porphyrin.
• The section containing the Fe2+
surrounded by the nitrogen
porphyrin ring is called “haem”.
• A fifth nitrogen is attached to a
larger protein called “globin”.
• What is the sixth bond?
Haemoglobin
• The sixth bond is with water or
oxygen.
• This is how oxygen is carried
around the body through the
blood.
• O2 is not a very good ligand
(weak bond with Fe2+) so easily
given up to cells.
• However, CO binds irreversible
(forms stable complex) and
destroys haemoglobin’s ability
to carry oxygen.
15.3 Coloured Ions
Learning Objectives:
1. Describe the factors that determine the colour of a complex ion.
2. Link the colour to electronic configuration.
Why are transition metal ions coloured?
• Part filled d-orbitals
• Possible for electrons to move from one d-orbital to another.
• Compounds have d-orbitals of slightly different energy levels.
• Electrons absorb energy and move up to a higher energy level.
• Wavelength of the energy is equal to the difference in energy.
• This wavelength of light is removed and the other colours are
reflected (the colour you see).
Amount of energy
ΔE = hν
• ΔE : amount of energy
• h = Planck’s constant
• ν = frequency of light absorbed
What colour?
• Large energy gap  Higher frequency of
light  Violet absorbed
• Complementary colour reflected:
• Appears
• Small energy gap  Lower frequency 
Red is absorbed
• Complementary colour reflected:
• Appears Green
What affects the colour?
• Metal Ion
• Oxidation State
• Coordination number
• Ligands
• Spectrometry can be used to determine the concentration of a solution
by measuring how much light it absorbs.
• Filter is used to only allow through the colour of light absorbed by the
substance being tested.
• A colorimeter detects how much light has been absorbed and the
concentration of the sample can be calculated.
Calibration graph
• Solutions of known
concentration are tested.
• The results are plotted
on a calibration graph.
• The concentration of the
unknown sample can
then be predicted using
the calibration graph.
15.4 Variable Oxidation States
Learning Objectives:
1. Recall that transition elements have variable oxidation states.
2. Recall the equilibrium reaction between chromium, chromate (VI)
ions and dichromate(VI) ions.
3. Recall the oxidation reaction of Co2+ and Cr3+ ions by water.
4. Recall the oxidation of Co2+ ions by air.
5. Represent these equations using half equations.
Redox of Transition Elements
• Transition elements commonly undergo redox reactions as they have
more than one stable ion.
Example:
• Write out the half equation for Fe2+ ions reacting with Cl2 gas to form
Fe3+ ions and Cl- ions.
• Write out the balanced redox reaction.
• What is oxidised? What is reduced?
• What is the oxidising agent? What is the reducing agent?
Half Equations
• Fe2+  Fe3+ + e• Cl2 + 2e-  2ClBalanced Redox Equation
• 2Fe2+ (aq) + Cl2 (g)  2Fe3+ (aq) + 2Cl- (aq)
• Fe2+ is oxidised (+2  +3), Cl2 is reduced (0-1)
• Cl2 is the oxidising agent and Fe2+ is the reducing agent.
• Potassium manganate (VII) can act as an oxidising agent in acidic
conditions (H+ aqueous).
• KMnO4
• MnO4- is reduced to Mn2+
• Write the balanced redox equation for Fe2+ being oxidised to Fe3+ by
potassium manganite (VII) in acidic conditions.
• Potassium manganite (VII) is soluble so forms K+ and MnO4- ions.
• MnO4- + 5e-  Mn2+
• MnO4- + 8H+ + 5e-  Mn2+ + 4H2O
(+7  +2)
• Fe2+  Fe3+ + e• 5Fe2+  5Fe3+ + 5e-
(+2  +3)
• MnO4- + 5Fe2+ + 8H+  Mn2+ + 5Fe3+ + 4H2O
Redox Titrations
• Redox reactions can be used instead of neutralisation reactions in a
titration to determine the concentration of an oxidising or reducing
agent in solution.
• Acidified potassium manganate(VII) (oxidising agent) can be used to
react with a reducing agent to determine it’s concentration.
• Potassium manganate(VII) is deep purple and is used to self indicate
as the purple colour disappears when the ions are reduced.
• If the purple colour remains, that means that all the reducing agent
has been oxidised (leaving leftover oxidising agent).
Chromium ions
Oxidation State
+6
+3
Formula of Ion
Cr2O72(dichromate)
CrO42(chromate)
Cr3+
Green/Violet
+2
Cr2+
Blue
+6
Colour
Orange
Stable In
Acid
Yellow
Alkali
Reactions with Chromium Ions