IB Chemistry S3.1.8 Properties of Transition Elements Notes

What Makes an Element a Transition Element

1. Transition elements sit in the d-block of the periodic table.
2. They are defined by having a partially filled d-sublevel in the atom or in at least one of their stable ions.
3. Two d-block elements are excluded by this definition: scandium and zinc.
   1. Scandium forms only Sc³⁺, which has an empty 3d sublevel (no d electrons).
   2. Zinc forms only Zn²⁺, which has a full 3d¹⁰ sublevel.

Electron Configuration and the d-Sublevel

1. Transition elements lie mainly in groups 3 to 11.
2. Their configurations follow the pattern $(n-1)d^{1-10}ns^{0-2}$, with the 4s filling before the 3d.

Why Scandium and Zinc Are Excluded

The Characteristic Properties of Transition Elements

A partially filled d-sublevel gives transition elements a set of shared, characteristic properties.

Variable Oxidation States

1. Transition elements form ions with more than one oxidation state.
2. The 4s and 3d electrons are close in energy, so both can be lost in bonding; S3.1.9 covers this in detail.

Coloured Complexes

1. Ligands split the d-orbitals, and d-electron transitions absorb visible light, so transition metal complexes are coloured.
2. The colour depends on the metal, its oxidation state, and the ligands; S3.1.10 covers the mechanism and the calculations.

Formation of Complex Ions

1. Transition metal ions accept electron pairs from ligands through coordinate bonds to form complex ions.
2. Coordinate bonding and ligands are developed in S2.2.3 and R3.4.8.

High Melting Points

Delocalised 4s and 3d electrons create strong metallic bonding, giving transition metals high melting and boiling points.

Catalytic Activity

1. Transition elements and their compounds are widely used as catalysts.
2. Their variable oxidation states and surfaces form temporary bonds with reactants, which lowers the activation energy.

Magnetism

1. Many transition metals and their ions are magnetic because of unpaired electrons in the d-sublevel.
2. The magnetism arises from the spin of these unpaired electrons.
3. Paramagnetism: Unpaired electrons cause weak attraction into a magnetic field, as in iron (Fe) and nickel (Ni).
4. Diamagnetism: All electrons are paired, so there is no net attraction, as in zinc (Zn).
5. Ferromagnetism: Unpaired electrons align permanently in the same direction, as in iron (Fe).