Transition metals, Ti → Cu, have special properties because they have incomplete d-electron sub-shells. This allows them to form complexes consisting of a central metal atom surrounded by several ligands. These ligands can either be mono- or multidentate.
Some transition metals are brightly coloured due to the unique spacing between their d sub-levels. The d-electrons absorb certain wavelengths of light and are moved up to an excited state, the remaining wavelengths of visible light are reflected and seen as colour.
Transition metals are special as they have variable oxidation states, allowing them to form multiple stable ions. The free, neutral form of each transition metal has an oxidation state of 0 [Sc₍₅₎ = Sc⁰]. For ions, the oxidation state is the same number as the charge [V³⁺= V''']. The oxidation state of a transition metal in a complex can be calculated by subtracting the charges of the individual atoms from the overall charge of the complex [TiCl₄ = Tiˡⱽ].
Their ability to form multiple stable oxidation states make transition metals very useful as catalysts. Transition metal catalysts are divided into two types, heterogeneous and homogenous, depending on whether they share the same phase as the reacting substances
Transition metals are much harder than group 1 elements, and have higher melting points. But the electron configuration of group 1 elements makes them much more reactive than transition metals.
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