Question

How do atomic radius vary in a period and in a group . 1?

Answer 1

Left to right , atomic radius decreases since the nuclear effective charge increases nd the atom contracts towards the centre
Down the group, atomic radius increases since the nuclear effective charge increases nd the atom expands .....

Hope this helps!!!!

Answer 2

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Atomic radius of the elements generally decreases from left to the right in a period because on moving from left to right in a period the nuclear charge gradually increases by one unit and one electron is also added in the electron shell. Due to this the electrons get attracted more and more towards the nucleus consequently the atomic radii decrease.

Atomic radius of the elements increases as we move downwords in a group because on moving down a group there is an increase in principal quantum number and thus, increase in the number of electron shells. Therefore the atomic size is expected to increase.