HL

The Transition Elements

Defining the d-block: Why Zinc doesn't make the cut.

1. The Strict IUPAC Definition

"An element whose atom has a partially filled d-subshell, or which can give rise to cations with an incomplete d-subshell."

Zinc (Zn) — The Imposter

Atom: \([Ar]3d^{10}4s^2\) (Full)
Ion (Zn²⁺): \([Ar]3d^{10}\) (Full)

NOT a transition metal.

Result: Colorless, Diamagnetic.

Scandium (Sc) — The Edge Case

Atom: \([Ar]3d^1\,4s^2\) (Incomplete) → YES

IS a transition metal.

Note: Its only ion \(Sc^{3+}\) is empty (\(3d^0\)), so compounds are clear.

2. Characteristic Properties

Variable Oxidation States

The 4s and 3d energies are very close. Electrons can be removed from both without huge energy jumps.
Example: \(Fe^{2+}\) and \(Fe^{3+}\).

Catalytic Activity

Heterogeneous: Iron in Haber Process (surface adsorption).
Homogeneous: \(Fe^{2+}\) in Heme groups.

Magnetism

Paramagnetism: Caused by unpaired electrons (attracted to magnet).
Diamagnetism: All electrons paired (weakly repelled). Zn is diamagnetic.