Final answer:
Atomic radius decreases across a period from left to right and increases down a group on the periodic table.
Explanation:
Atomic radius is a measure of the size of an atom, usually defined as the distance from the nucleus to the outer electron shell. In the periodic table, the trend for atomic radius is that it decreases as you move from left to right across a period and increases as you move down a group.
The increasing positive charge of the nucleus as you move across a period exerts a tighter grip on the valence electrons, leading to a decrease in atomic radius. Conversely, moving down a group allows for additional electron shells, resulting in an increase in atomic radius.
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