Across a period from left to right, the atomic radius generally:

Atomic radius **decreases** from left to right across a period. Why: nuclear charge ($Z$) increases by 1 as you move right, pulling electrons closer. The added electron enters the same shell so screening barely increases — the net effect is stronger attraction and smaller radius. Across period 2: Li (152 pm) → Be → B → C → N → O → F (72 pm). Roughly halves. Down a group, atomic radius *increases* (electrons go into higher principal shells, further from nucleus).