Question

why does atomic radius change as we move from left to right in a period?

Answer 1

As we move towards the right in a period the number of protons keep on increasing. As the protons increase, the nuclear charge also increases. But the number of shells remain same. Thus, the size of the atom decreases and the atomic radius also decreases.

Answer 2

Atomic radius changes because as we move from left to right in a period, the no. of protons in the nucleus increases. Increase in the no. of protons means increase in nuclear charge which pulls the electrons towards itself. Hence, the atomic radius decreases.