Question

What are inner transition elements?

Answer 1

The inner transition elements have two series of elements.

• Lanthanoids
• Actinoids

1. Lanthanoid series consists of 14 elements from Cerium (₅₈Ce) to Lutetium (₇₁Lu) following Lanthanum (₅₇La). These elements are characterised by the preferential filling of 4f orbitals.

2. Actinoids consist of 14 elements from Thorium (₉₀Th) to Lawrencium (₁₀₃Lr) following Actinium (₈₉Ac). These elements are characterised by the preferential filling of 5f orbital.

The elements which in their elemental or ionic form have partly filled f-orbitals are called f-block elements.

As the f-orbitals lie inner to the penultimate shell, therefore these elements having partially filled f-orbitals, are also called inner transition elements.