How does atomic radius change across a period?

The atomic radius decreases across a period primarily due to the increasing nuclear charge without a corresponding increase in shielding. As you move from left to right across a period in the periodic table, protons are added to the nucleus, which increases its positive charge. This stronger positive charge exerts a greater attractive force on the surrounding electrons.

While electrons are also being added across the period, they are being added to the same energy level, meaning that the shielding effect remains relatively constant. Since the increased positive charge from the nucleus pulls the electrons closer, the overall size of the atom decreases.

This trend plays a vital role in understanding the behavior of elements in chemical reactions and bonding, as the smaller atomic radius generally leads to greater electronegativity and influences how atoms interact with each other.