Question

Why does atomic radii decrease as we move left or right in a period of periodic table

Answer 1

As we move from left to right, there is a consecutive addition of one proton in the nucleus and one electron in the valence shell of the element. However, the electron is always added in the same valence shell of the element. The addition of proton in the nucleus increases the positive charge, which consequently pulls the extra-nuclear electrons in the outermost shell inward. Thus, atomic radius decreases with the increase in the number of protons as one moves from left to right in a period.

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