The atomic radius exhibits distinct trends on the periodic table: it generally decreases across a period and increases down a group, primarily due to variations in electron configurations.

The atomic radius is fundamentally influenced by an atom’s electron configuration. As one moves from left to right across a period in the periodic table, the atomic radius tends to decrease. This decrease can be attributed to the fact that each successive atom has an additional proton and an additional electron compared to the previous atom. The added proton enhances the positive charge of the nucleus, which in turn attracts the electrons in the electron cloud more strongly, pulling them closer to the nucleus and resulting in a smaller atomic radius.

Conversely, as one moves down a group in the periodic table, the atomic radius generally increases. This increase occurs because each atom in the group possesses an additional energy level compared to the one above it. Each new energy level is situated further from the nucleus, leading to an overall increase in atomic radius. The influence of the additional energy level is more significant than the effect of the additional proton, thereby causing the atomic radius to expand.

The electron configuration also plays a crucial role in determining atomic radius through what is known as the shielding effect. The shielding effect refers to the reduction in the effective nuclear charge experienced by the outer electrons, caused by the repulsive forces from electrons in inner energy levels. These inner electrons effectively shield the outermost electrons from the full positive charge of the protons in the nucleus. As a result, the outer electrons experience a weaker attraction to the nucleus, which contributes to an increase in the atomic radius.

In summary, the atomic radius is influenced by several factors related to an atom’s electron configuration. The number of protons, the number of energy levels, and the shielding effect all significantly impact the atomic radius. As one traverses a period from left to right, the atomic radius typically decreases due to the increasing number of protons. In contrast, as one moves down a group, the atomic radius generally increases because of the addition of energy levels. Additionally, the shielding effect further enhances the increase in atomic radius as one descends a group.