How do rationalize atomic size on the basis of an element's position on the Periodic Table?

Question

Caleb Adams · Accepted Answer

Atomic size DECREASES across a Period....

Atomic size DECREASES across a Period, a row of the Periodic Table, from LEFT to RIGHT as we face the Table. It INCREASES down a Group.

This is one of the most important manifestations of atomic structure; i.e. the diminution in size across the Period. Atomic size is a function of (i) nuclear charge, thus higher #Z# SHOULD have smaller radius; and (ii) shielding by other electrons. Incomplete electronic shells shield the nuclear charge VERY imperfectly....

Taken together, these two principles rationalize the actual data...

Especially, for the first few short Periods, do these data support what we have argued? And so for a given Period, which is the largest atom?

Serenity Allen · Answer

undefined Atomic size generally decreases from left to right across a period and increases from top to bottom within a group on the periodic table. This trend is primarily attributed to changes in the effective nuclear charge and the number of electron shells as you move across and down the periodic table, respectively. Specifically, as you move across a period, the effective nuclear charge increases due to the increasing number of protons in the nucleus, resulting in a stronger attraction between the nucleus and the outermost electrons, thus decreasing atomic size. Conversely, as you move down a group, the number of electron shells increases, leading to greater distance between the nucleus and the outermost electrons, thereby increasing atomic size.