Reactions of Transition Metal Elements

Understand that transition metals often form coloured compounds, thanks to their partially filled d sub-levels. The colour of these compounds is due to the absorption of certain wavelengths of light, resulting in the emission of visible light of a complementary colour.
Note that transition metals exhibit variable oxidation states. This is due to the small energy difference between 4s and 3d sub-levels. As a result, both 4s and 3d electrons are available for bonding and ionisation, which results in multiple stable charges for these elements.
Recall that transition metals readily form coordination compounds. This is due to the presence of empty d orbitals that can accept lone pairs of electrons from ligands (donor molecules or ions).
Remember that some transition metals can be both oxidising and reducing agents. Mn in MnO4- can be reduced from +7 to +2, while Cu in Cu+ can be oxidised to Cu2+.
Recognise that transition metals are often effective catalysts, both in their elemental form and as compounds. They offer alternative, lower-energy pathways for reactions, without being consumed themselves. The most common examples are iron in the Haber process and nickel in the hydrogenation of alkenes.
Understand that complex ions of transition metals can exhibit optical isomerism. This is due to non-superimposable mirror images being formed, thanks to the arrangement of ligands around the central metal ion.
Be aware that transition metals and their compounds often show magnetic properties due to the presence of unpaired electrons in d orbitals.
Understand that the “splitting” of d orbitals in transition metal complex ions leads to colour. Different ligands lead to different extents of splitting and therefore different colours.
Be able to explain the catalytic properties of transition metals by two methods: changing reaction pathways to lower activation energy or providing a surface for the reaction to occur.
Remember that the catalytic converters in cars often use transition metals such as platinum, palladium, and rhodium. These metals catalyse reactions that convert toxic gases into less harmful substances.