Question

why atomic size decreases across a period

Answer 1

because as we move across the period the distance between valence electrons and nucleus increases and nuclear force of attraction increases..so the atoms are of small size

Answer 2

when we move across the period the atomic number increases but no. of shells remain same.
Du to increase in nuclear charge the electrons are attracted with more power towards the nucleus.
Therefore the size of the atom shrinks or decreases.



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