Question

Lanthanoid contraction is caused due to ______.

Options

• the appreciable shielding on outer electrons by 4f-electrons from the nuclear charge.

• the appreciable shielding on outer electrons by 5d-electrons from the nuclear charge.

• the same effective nuclear charge from Ce to Lu.

• the imperfect shielding on outer electrons by 4f-electrons from the nuclear charge.

Answer 1

Lanthanoid contraction is caused due to the imperfect shielding on outer electrons by 4f-electrons from the nuclear charge.

Explanation:

The unique geometry of 4f-orbitals makes it extremely difficult for one 4f-electron to be shielded from a growing nuclear charge by another. Therefore, each 4f-electron undergoes an increase in effective nuclear charge as the atomic number rises. With each additional electron in the 4f-subshell, this results in a slight size reduction.