what is actinide contraction

Actinide contraction is the gradual decrease in atomic and ionic radii of actinide elements as their atomic number increases from thorium to lawrencium.

Quick Scoop: What is actinide contraction?

As you move across the actinide series (Actinium, Thorium … up to Lawrencium), each next element has:

• One more proton in the nucleus (higher nuclear charge).

• One more electron entering the 5f subshell.

Because 5f electrons shield the nuclear charge poorly, the outer electrons feel a stronger pull from the nucleus.

This stronger attraction pulls electrons closer, so the size (atomic and ionic radii) steadily decreases across the series: this trend is called actinide (or actinoid) contraction.

Key points in bullet form

• Actinides: elements with atomic numbers 89–103 (Ac to Lr).

• Phenomenon: steady decrease in atomic and ionic radii with increasing atomic number.

• Main cause: poor shielding of 5f electrons, leading to high effective nuclear charge felt by outer electrons.

• Effect: atoms and ions become smaller across the series, and this contraction is even stronger than lanthanide contraction because 5f shielding is worse than 4f shielding.

One-line textbook-style definition

Actinide contraction is the gradual decrease in the atomic and ionic radii of actinide elements with increasing atomic number due to poor shielding by 5f electrons and increasing nuclear charge.

Information gathered from public forums or data available on the internet and portrayed here.