Question

What are the characteristics of the transition elements and why are they called transition elements?

Answer 1

1. Electronic configuration: General electronic configuration is (n − 1) d¹⁻¹⁰ns⁰⁻². This configuration reflects the filling of d-orbitals in addition to the s-orbitals of the outermost shell.
2. Metallic character: Transition elements, except for Zn, Cd and Hg, exhibit metallic structures and typical metallic properties like malleability, ductility and conductivity.
3. Atomic and ionic size: Across a transition series, the atomic and ionic radii decrease due to the increasing nuclear charge, which pulls the d-electrons closer to the nucleus (a phenomenon called the lanthanide contraction).
4. Oxidation state: They exhibit variable oxidation states due to the participation of both d and s-electrons in bonding. Common oxidation states range from +2 to +7, depending on the element.
5. Paramagnetism: Ions with unpaired d-electrons exhibit paramagnetism. The greater the number of unpaired electrons, the stronger the paramagnetic behaviour.
6. Ionisation enthalpy: Ionisation enthalpy increases gradually across the series as the nuclear charge increases, making it harder to remove electrons.
7. Formation of coloured ions: Transition metal ions are often colored because of electronic transitions within the d-orbitals (specifically d-d transitions) when they absorb visible light.
8. Formation of complex compounds: Transition metals form complexes due to their small size, high charge density, and availability of vacant d-orbitals to accept electron pairs from ligands.
9. They possess catalytic properties: They act as catalysts because they can exist in multiple oxidation states, which facilitates various chemical reactions.
10. Formation of interstitial compounds: Transition metals can form interstitial compounds by trapping small non-metal atoms (such as H, C, or N) within their crystal lattice.
11. Alloy formation: They readily form alloys due to similar atomic sizes, which allows different metal atoms to substitute for one another in the crystal structure.

They are positioned between s and p-block elements and are known as transition elements because of their incompletely filled d-orbitals in the ground state or any stable oxidation state.