What trend is observed in atomic radius as one moves from top to bottom in the periodic table?

As you move from top to bottom in the periodic table, the atomic radius increases. This trend is primarily due to the addition of electron shells, or energy levels, as you progress down a group. Each time a new period is started, an additional shell of electrons is added to the atom.

The overall effect of these additional shells is that the outermost electrons are farther from the nucleus, which increases the size of the atom. Although the nuclear charge increases (more protons in the nucleus), the shielding effect caused by the inner-shell electrons becomes more significant. The inner-shell electrons repel the outer-shell electrons, counteracting the pull from the nucleus and allowing the atomic radius to expand.

This trend is consistent across the periodic table and is a fundamental concept in understanding the properties of elements. It helps explain various chemical behaviors and reactivities of elements as well, especially in terms of their bonding and interaction with other atoms.