Question

give the trends in atomic size on moving: down the group, across the period left to right

Answer 1

On Moving Left to right across a period , the atomic size decreases and the nuclear charge increases but the shell remains same

On moving top to bottom in a group size of atom Increases as the increase in shell is more significant than increase in nuclear charge .

Answer 2

As you move down the group as you know the elements in A group belong to a particular family hence the change in atomic size is expected significantly but as you know as more and more number of shells are added as you go down a group nuclear charge ( ability of a nucleus to attract its electrons) decreases and hence atomic size increases.

In a period as we go from right to left more and more sub shells are added within the main shell and hence nuclear charge increases and atomic size decreases significantly. I hope you find it helpful