15A: Principles of transition metal chemistry
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Define transition metals.
D-block elements that form one or more stable ions with incompletely-filled d-orbitals.
State why transition metals show variable oxidation number.
There is only a gradual increase in successive ionisation energies.
Describe what is meant by the term ‘ligand’.
A species that uses a lone pair of electrons to form a dative covalent bond with a metal ion.
State the type of bonding involved in the formation of complex ions.
Dative (coordinate) bonding
Describe a complex ion.
A central metal ion surrounded by ligands.
Explain the colours of complex ions.
Ligands donate electrons, So repulsion in d-orbitals increases, So d-orbitals split into 2 energy levels. Electrons can absorb certain frequencies of light and promote to higher d-orbitals, So only the remaining light is transmitted.
Explain why there is a lack of colour in some aqueous ions and other complex ions.
Electrons cannot move between d orbitals in ions with an empty or full d sub-shell.
State 3 changes in transition metal ions that may result in colour changes.
Oxidation number Ligand (e.g. type, orientation) Coordination number
Define the term ‘coordination number’.
The number of dative (coordinate) bonds formed with the metal ion.
State why H2O, OH− and NH3 act as monodentate ligands.
They can only use one lone pair to form a dative (coordinate) bond with a metal ion.
State and explain the shape of complexes with six-fold coordination.
Octahedral. Electron pairs in dative (coordinate) bonds will take a position with minimum repulsion.
State the shape of complexes with relatively large ligands such as Cl-.
Tetrahedral.
Give an example of a square planar complex formed by transition metal ions.
Cis-platin
Explain why cis-platin used in cancer treatment is supplied as a single isomer and not in a mixture with the trans form.
Only the cis isomer is effective at preventing cell division.
Identify the type of ligand of NH2CH2CH2NH2.
Bidentate
Identify the type of ligand of EDTA4-.
Multidentate (Hexadentate)
Describe haemoglobin
An iron(II) complex containing a multidentate ligand.
State the type of reaction that occurs when an oxygen molecule bound to haemoglobin is replaced by a carbon monoxide molecule.
Ligand exchange reaction