Question

All the transition elements are d-block elements but all d-block elements are not transition elements. Justify

Answer 1

Those elements which either themselves or their ions have incompletely filled d-orbitals are called transition elements. They are all d-block elements because ‘d’ orbitals are progressively filled.
But those d-block elements or their ions which do not have incompletely filled d-orbitals are not transition elements, e.g., Zn, Cd and Hg are d-block elements but not transition metals.

We can conclude that,

A transition metal is one which forms one or more stable ions which have incompletely filled d orbitals. On the basis of this definition, scandium and zinc do not count as transition metals - even though they are members of the d block.

• Scandium has the electronic structure [Ar] 3d14s2. When it forms ions, it always loses the 3 outer electrons and ends up with an argon structure. The Sc3+ ion has no d electrons and so does not meet the definition.
• Zinc has the electronic structure [Ar] 3d104s2. When it forms ions, it always loses the two 4s electrons to give a 2+ ion with the electronic structure [Ar] 3d10. The zinc ion has full d levels and does not meet the definition either.

By contrast, copper, [Ar] 3d104s1, forms two ions. In the Cu+ ion the electronic structure is [Ar] 3d10. However, the more common Cu2+ ion has the structure [Ar] 3d9. Copper is definitely a transition metal because the Cu2+ ion has an incomplete d level.