What trend is seen in atom size going down the peroidic table?

As you move down the Periodic Table, the size of atoms generally increases. This trend occurs because additional electron shells are added with each successive element, which increases the distance between the nucleus and the outermost electrons. Additionally, the increased shielding effect from inner-shell electrons reduces the effective nuclear charge felt by the outer electrons, allowing them to spread out more. Consequently, this leads to larger atomic radii for elements lower in a group.