Question

define atomic size. how does it vary in a group or a period

Answer 1

the atomic size means the distance between the nucleus of atom and the valence electron....

the atomic size increases down the group ....as the new shells are added ....

and along the period ...the atomic size decreases from left to right...as the more electrons were added in last shell....

Answer 2

Atomic size is the difference between  nucleus and outer orbit  .                          it decreases in rows of periodic table.       And increase in column