3.10 How do atomic radius vary in a period and in a group? How do you explain the variation?
Atomic radius generally decreases from left to right across a period. This is because within
a period, the outer electrons are present in the same valence shell and the atomic number
increases from left to right across a period, resulting in an increased effective nuclear
charge. As a result, the attraction of electrons to the nucleus increases.
On the other hand, the atomic radius generally increases down a group. This is because
down a group, the principal quantum number (n) increases which results in an increase of
the distance between the nucleus and valence electrons.
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