Assign reasons for the following:
Transition metals and their many compounds act as good catalyst.
Actinoid contraction is greater from element to element than lanthanoid contraction. Why?
In actinoids, 5f orbitals are filled. These 5forbitals have a poorer shielding effect than 4f orbitals (in lanthanoids). Thus, the effective nuclear charge experienced by electrons in valence shells in case of actinoids is much more that that experienced by lanthanoids. Hence, the size contaction in actinoids is greater as compared to that in lanthanoids.
Scandium (Z = 21) does not exhibit variable oxidation states and yet it is regarded as a transition element.
What may be the possible oxidation states of the transition metals with the following d electronic configurations in the ground state of their atoms: 3d34s2,3d54s2 and 3d64s2. Indicative relative stability of oxidation states in each case.