Question

Explain why Scandium (Z=21) is a transition element while Zinc (Z=30) is not.

Hint:

Elements of group 12 (Zn, Cd, Hg) are not true transition elements because their d-orbitals are completely filled.

Answer 1

Concept: A transition element is defined as an element that has:
A partially filled d-orbital in its ground state, or
Forms at least one ion with an incomplete d-subshell.

Electronic Configuration: Scandium (Z = 21): \[ \text{Sc}: [Ar] \, 3d^1 4s^2 \]
Contains one electron in the \(3d\) orbital.
d-subshell is partially filled.
Hence, it satisfies the definition of a transition element.

Zinc (Z = 30): \[ \text{Zn}: [Ar] \, 3d^{10} 4s^2 \]
d-orbital is completely filled (\(3d^{10}\)).
Common ion: \( \text{Zn}^{2+} = [Ar]\,3d^{10} \)
d-subshell remains fully filled even after ion formation.

Conclusion:
Scandium: Partially filled d-orbital → Transition element.
Zinc: Fully filled d-orbital in atom and ion → Not a transition element.