Question

How does the size of atoms vary from left to right in a period, and on descending a group in the periodic table? what are the reasons u these changes?

Answer 1

The atomic size increases from the top to the bottom in any group as a result of increases in all of the three factors. (As the number of energy levels increases, the size must increase.) Going across a period (from left to right), the number of protons increases and therefore the nuclear charge increases.