answer:
the number of energy levels increases as you move down a group! as the number of electrons increases each subsequent energy level is further from the nucleus than the last.
so
the atomic radius increases as the group and energy levels increase
explanation:
as you go across a period, electrons are added to the same energy level. at the same time, protons are being added to the nucleus. the concentration of more protons in the nucleus creates a higher effective nuclear charge,
so like basically,
there is a stronger force of attraction pulling the electrons closer to the nucleus resulting in a smaller atomic radius.
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