Question

Justify the following with suitable reasons: Atomic size decreases as we move across a period.

Answer 1

on going from left to right, electrons add in the valence shell likewise protons add in the nucleus. The effective nuclear charge on the electrons increase ( remember that one electron is not pulled by one proton but each electron is pulled by all protons equally, i.e. more protons in nucleus= more pull for every electron) due to which the valence electrons are pulled closer to the nucleus and overall atomic size decreases.