A2-Level Transition Elements
Transition metals have variable oxidation states, enabling them to form ions with different charges.
These ions can lose or gain electrons to form another stable ion than can then gain or lose electrons to reform the original ion.
In a reaction, this means a transition metal can provide an alternative route and allow a species to be oxidized and then another species to be reduced, whilst remaining unchanged overall.
This means the transition metal is acting as a catalyst.
Transition metals have variable oxidation states, allowing them to form ions with different charges. The ability to lose or gain an electron to change oxidation state and then re-form the original oxidation state allows transition metal ions to ‘help’ in a reaction but remain unchanged, making them very good catalysts.
The partially filled d-orbitals enable this to happen. It is a little bit like a bus driving around with at least one back seat free – it can easily ‘pick up’ another passenger and then ‘drop off’ that passenger later on, or it can drop off a passenger and then pick up another one later on.
The same is true for the transition metal ions, an electron can ‘hop in’ to an empty orbital, enabling another species to be oxidised, and then later on in the reaction, it can ‘hop out’ of the orbital, allowing another species to be reduced. Equally, an electron already in a d-orbital can ‘hop out’ and reduce another species, and then later in the reaction, another electron can ‘hop back in’ to oxidise another species. In both cases, although the transition metals oxidation state changes to help the reaction happen, the oxidation state of the metal is the same at the end as at the start.