Topic 15 – Transition Metals
In order to develop their practical skills, students should be encouraged to carry out a range of practical experiments related to this topic. Possible
experiments include the stepwise reduction of vanadium(V) to vanadium(II), investigating the reactions of copper(II) ions or chromium(III) ions, using
sodium hydroxide and ammonia solution to identify transition metal ions, investigating autocatalysis, preparing a complex transition metal salt.
Mathematical skills that could be developed in this topic include investigating the geometry of different transition metal complexes. Within this
topic, students can consider the model for the filling of electron orbitals encountered in Topic 1, and see how limitations in that model indicate the
need for more sophisticated explanations. They can also appreciate that catalyst research is a frontier area, and one which provides an opportunity
to show how the scientific community reports and validates new knowledge.
Topic 15A: Principles of transition metal chemistry
1. be able to deduce the electronic configurations of atoms and ions of the d-block
elements of period 4 (Sc–Zn), given the atomic number and charge (if any)
State the full electronic configuration for the vanadium atom and the V 3+ ion.
V = 1s22s22p63s23p64s23d3
V3+= 1s22s22p63s23p63d2 (remember you both gain and lose 4s before 3d!)
2. know that transition metals are [REDACTED]
Give the definition of a transition metal. Hence, explain why zinc is not classified as a transition metal.
A transition metal is an element that forms ions with partly filled d-orbitals. Zinc’s only ion (Zn 2+) has a full d-subshell.
3. understand why transition metals show variable oxidation number
Chromium has the electronic config [Ar]3d54s1. Why is KCrO4 unlikely to exist?
KCrO4 would give Cr an oxidation state of +7, which is unlikely as it would need to remove an electron from the 3p
subshell. This requires far more energy than removing electrons from the 4s/3d subshells.
Why does chromium (and all transition metals) exhibit variable oxidation states?
The energy levels of the 3d and 4s subshells are similar. This allows electrons to be readily lost or shared from either
subshell, leading to multiple stable oxidation states being possible.
4/5/6. know what is meant by ‘ligand’ and ‘complex ion’, and know dative bonding is involved in these ions
Well? What is meant by the term 'ligand’?
A ligand is a molecule or anion bound to a central metal ion in a complex ion by dative covalent bonding.
7/8. know transition metals form coloured ions, and understand that the colour of aqueous ions, and other
complex ions, results from the splitting of the energy levels of the d-orbitals by ligands
Transition metal complexes are usually coloured. Explain how the colours occur.
Transition metal ions are coloured because d-electrons can absorb light of a certain frequency, and get excited into
higher energy d-orbitals. The resultant light is thus missing certain frequencies and so is coloured. The size of the
energy gap determines the colour. To do this, the d-orbitals must be split, and partially filled. D-electrons can only
absorb light and ‘jump up’ energy levels here as the 3d subshell has been split by the ligands bonding to the central
metal ion.
, 9. understand why there is a lack of colour in some aqueous ions and other complex ions
Suggest why the very strong interactions between the F- ligands and the Fe3+ ion result in the complex [FeF6]3-
being colourless.
The strong interaction results in a very large energy gap between the d-orbitals, so that the wavelength absorbed is
in the UV region of the EM spectrum.
Explain why zinc ions are colourless in a complex ion, whilst iron(II) ions do have colour.
Zinc is not a transition metal as it has a full d-orbital as an ion, so electrons cannot absorb light and be promoted to
higher energy levels.
10. understand that colour changes in transition metal ions may arise due to changes in: i oxidation number,
ii ligand, iii coordination number
Explain briefly why the above three factors cause a change in colour.
Changing any one of these factors changes the size of the energy gap between the d-orbitals.
11. understand the meaning of the term ‘coordination number’
Give the definition of the term 'coordination number’.
Coordination number is the number of coordinate (dative) bonds to the metal ion from the surrounding ligands.
12. understand why H2O, OH− and NH3 act as monodentate ligands
Why are the above three molecules monodentate ligands?
They have a single lone pair that can form a dative covalent bond.
13. understand why complexes with six-fold coordination have an octahedral shape, such as those formed
by metal ions with H2O, OH− and NH3 as ligands
Explain why regular hexacomplexes form octahedral shapes.
The complex ions obey VSEPR theory – i.e. the pairs of electrons in the dative bonds between ligand and metal ion
are spaced apart to minimise repulsive forces. For six electron pairs, an octahedral shape obeys this process.
14. know that transition metal ions may form tetrahedral complexes with relatively large ligands such as Cl −
Explain why larger ligands form tetrahedral complexes.
Larger ligands have larger electron clouds, which repel each other and restrict the number of ligands that can be
fitted around the central metal ion.
15. know square planar complexes are formed by transition metal ions and cis-platin is an example of this
Which elements form square planar complexes?
Yeah it’s really just platinum ions.
16. understand why cis-platin used in cancer treatment is a single isomer and not a mixture with the trans
Why must only a single enantiomer of cis-platin be used?
Trans-platin is not nearly as effective as an anti-cancer drug, and is far more toxic than cis-platin.
2
In order to develop their practical skills, students should be encouraged to carry out a range of practical experiments related to this topic. Possible
experiments include the stepwise reduction of vanadium(V) to vanadium(II), investigating the reactions of copper(II) ions or chromium(III) ions, using
sodium hydroxide and ammonia solution to identify transition metal ions, investigating autocatalysis, preparing a complex transition metal salt.
Mathematical skills that could be developed in this topic include investigating the geometry of different transition metal complexes. Within this
topic, students can consider the model for the filling of electron orbitals encountered in Topic 1, and see how limitations in that model indicate the
need for more sophisticated explanations. They can also appreciate that catalyst research is a frontier area, and one which provides an opportunity
to show how the scientific community reports and validates new knowledge.
Topic 15A: Principles of transition metal chemistry
1. be able to deduce the electronic configurations of atoms and ions of the d-block
elements of period 4 (Sc–Zn), given the atomic number and charge (if any)
State the full electronic configuration for the vanadium atom and the V 3+ ion.
V = 1s22s22p63s23p64s23d3
V3+= 1s22s22p63s23p63d2 (remember you both gain and lose 4s before 3d!)
2. know that transition metals are [REDACTED]
Give the definition of a transition metal. Hence, explain why zinc is not classified as a transition metal.
A transition metal is an element that forms ions with partly filled d-orbitals. Zinc’s only ion (Zn 2+) has a full d-subshell.
3. understand why transition metals show variable oxidation number
Chromium has the electronic config [Ar]3d54s1. Why is KCrO4 unlikely to exist?
KCrO4 would give Cr an oxidation state of +7, which is unlikely as it would need to remove an electron from the 3p
subshell. This requires far more energy than removing electrons from the 4s/3d subshells.
Why does chromium (and all transition metals) exhibit variable oxidation states?
The energy levels of the 3d and 4s subshells are similar. This allows electrons to be readily lost or shared from either
subshell, leading to multiple stable oxidation states being possible.
4/5/6. know what is meant by ‘ligand’ and ‘complex ion’, and know dative bonding is involved in these ions
Well? What is meant by the term 'ligand’?
A ligand is a molecule or anion bound to a central metal ion in a complex ion by dative covalent bonding.
7/8. know transition metals form coloured ions, and understand that the colour of aqueous ions, and other
complex ions, results from the splitting of the energy levels of the d-orbitals by ligands
Transition metal complexes are usually coloured. Explain how the colours occur.
Transition metal ions are coloured because d-electrons can absorb light of a certain frequency, and get excited into
higher energy d-orbitals. The resultant light is thus missing certain frequencies and so is coloured. The size of the
energy gap determines the colour. To do this, the d-orbitals must be split, and partially filled. D-electrons can only
absorb light and ‘jump up’ energy levels here as the 3d subshell has been split by the ligands bonding to the central
metal ion.
, 9. understand why there is a lack of colour in some aqueous ions and other complex ions
Suggest why the very strong interactions between the F- ligands and the Fe3+ ion result in the complex [FeF6]3-
being colourless.
The strong interaction results in a very large energy gap between the d-orbitals, so that the wavelength absorbed is
in the UV region of the EM spectrum.
Explain why zinc ions are colourless in a complex ion, whilst iron(II) ions do have colour.
Zinc is not a transition metal as it has a full d-orbital as an ion, so electrons cannot absorb light and be promoted to
higher energy levels.
10. understand that colour changes in transition metal ions may arise due to changes in: i oxidation number,
ii ligand, iii coordination number
Explain briefly why the above three factors cause a change in colour.
Changing any one of these factors changes the size of the energy gap between the d-orbitals.
11. understand the meaning of the term ‘coordination number’
Give the definition of the term 'coordination number’.
Coordination number is the number of coordinate (dative) bonds to the metal ion from the surrounding ligands.
12. understand why H2O, OH− and NH3 act as monodentate ligands
Why are the above three molecules monodentate ligands?
They have a single lone pair that can form a dative covalent bond.
13. understand why complexes with six-fold coordination have an octahedral shape, such as those formed
by metal ions with H2O, OH− and NH3 as ligands
Explain why regular hexacomplexes form octahedral shapes.
The complex ions obey VSEPR theory – i.e. the pairs of electrons in the dative bonds between ligand and metal ion
are spaced apart to minimise repulsive forces. For six electron pairs, an octahedral shape obeys this process.
14. know that transition metal ions may form tetrahedral complexes with relatively large ligands such as Cl −
Explain why larger ligands form tetrahedral complexes.
Larger ligands have larger electron clouds, which repel each other and restrict the number of ligands that can be
fitted around the central metal ion.
15. know square planar complexes are formed by transition metal ions and cis-platin is an example of this
Which elements form square planar complexes?
Yeah it’s really just platinum ions.
16. understand why cis-platin used in cancer treatment is a single isomer and not a mixture with the trans
Why must only a single enantiomer of cis-platin be used?
Trans-platin is not nearly as effective as an anti-cancer drug, and is far more toxic than cis-platin.
2
