What trend in atomic radius occurs as you move from left to right across a period in the periodic table?

As you move from left to right across a period in the periodic table, the atomic radius generally decreases. This trend occurs due to the increase in positive charge of the nucleus as protons are added. Each additional proton creates a stronger positive charge that pulls the surrounding electrons closer to the nucleus. Since the number of electron shells remains the same across a period, the increased nuclear charge effectively draws the electron cloud closer, leading to a reduction in atomic size.

Furthermore, the electrons being added to the outer shell do not significantly increase the shielding effect since they are being added to the same principal energy level. Therefore, the electrostatic attraction between the nucleus and the electrons increases, resulting in a smaller atomic radius. This decreasing trend continues consistently across the period until a new period begins, where a new electron shell is introduced, causing a larger atomic radius again.