Question

Why does atomic size of an element decreases down the group in the modern periodic table
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Answer 1

Answer:

On moving from left to right in a period, the atomic size decreases. More and more electrons are added to same shell. The attraction between nucleus and valence electrons increases with increase in the atomic number.

On moving down the group, from top to bottom, the atomic size increases. This is because with increase in the atomic number, extra shells of electrons are added.