How does atomic size change across a period of the periodic table?

Across a period of the periodic table, atomic radius generally decreases from left to right.1

While one might expect atoms to grow larger as more electrons are added, the opposite occurs due to an increase in nuclear charge. As you move across a period, the number of protons in the nucleus increases, creating a stronger positive charge. Because the additional valence electrons do not effectively shield each other from this growing nuclear pull, the nucleus draws the outer-shell electrons closer, resulting in a more compact atom.1

This trend is a result of the competition between the inflating effect of adding more electrons and the contracting effect of the stronger nuclear charge, with the latter typically dominating. Consequently, elements on the left side of a period are larger than those on the right.12