Explain the following facts : (a) Transition metals act as catalysts. (b) Chromium group elements have the highest melting points in their respective series. (c) Transition metals form coloured complexes.

Explain the following facts : (a) Transition metals act as catalysts.

1.	Explain the following facts : (a) Transition metals act as catalysts. (b) Chromium group elements have the highest melting points in their respective series. (c) Transition metals form coloured complexes.
Answer» Solution :(a) Transition metals have incomplete d-orbitals. They combine with the reactants to form intermediate products which change into final products. Transition metals provide a large surface area to the gaseous reactants to change into the products. (b) CHROMIUM group elements have the greatest number of unpaired electrons in d-orbitals. They are THUS CAPABLE of forming maximum interatomic metallic bonds. This raises the melting point of the chromium group elements. (c) Transition metals have incompletely filled d-orbitals and have unpaired electrons which are excited to higher energy d-orbitals in the same sub-shell (from `t_(2g)` to `e_(g)`). These are called d-d transitions. During this process, the molecules ABSORB energy from the visible region. The transmitted light is the colour shown by the substance.