AS Level Chemistry Practice Exam 2026 – Complete Prep Guide

As you move down a group in the periodic table, the atomic radius increases due to increased shielding effects. This increase occurs because each successive element down a group has an additional electron shell compared to the one above it. This addition of electron shells means that the outermost electrons are further away from the nucleus.

The increase in the number of inner electron shells leads to an increased shielding effect, where the inner electrons repel the outer electrons. This repulsion impacts the effective nuclear charge experienced by the outermost electrons, making it less effective in pulling them closer to the nucleus. As a result, even though the nuclear charge (the total number of protons in the nucleus) is higher as you move down a group, the significant shielding effect from the inner shells overrides this, causing the atomic radius to expand.

In summary, the increase in atomic radius down a group is primarily due to the added shells of electrons and the resulting shielding effect that weakens the pull of the nucleus on the outer electrons.