Why does atomic radius increase on moving down a group??

1.	Why does atomic radius increase on moving down a group??
Answer» As we go across a Period, a row, of the Periodic Table, from left to right as we FACE the Table, we add another positive charge (a proton, a fundamental, positively charged nuclear particle) to the nucleus. This results in a DECREASE in atomic radii across the Period, due to the increased nuclear charge which draws in the valence electrons.On the other hand, going down a Group, we go to another so-called shell of electrons, that build on the preceding shell. Atomic radii thus INCREASE down the Group. This contest between nuclear charge, i.e. Z, and shielding by other electrons, underlies the structure of the Periodic Table. And note that incomplete valence electronic shells, shield the nuclear charge VERY ineffectively.AS a scientist, however, you should seek data that inform your argument. And I leave this up to you. You want details of atomic radii only, not ionic radii! If you can remember Atomic size INCREASES down a Group, but DECREASES across a Period, where a Group is a column and Period is a row of the Periodic Table, you have mastered a fundamental principle of chemistry. On moving down a group, a new shell is being add to the atom which results in increased radius . Because on moving down the group, a new shell gets added to the atom which increases it\'s radii.

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