Question

How does the periodic trend of atomic radius relate to the addition of electrons?

Answer 1

Atomic radius of any element is the distance between the nucleus of that element up to which the electron cloud is extended. The atomic radius is of the order ${{10}^{-10}}m$.

Complete answer:
Periodic table consists of various trends related to atomic size, electronegativity, and electron affinity and ionization enthalpy of elements. These trends tend to change due to change in the structural properties of elements.
In a periodic table, atomic radius has a decrease as we move from left to right in a period, while it has an increase while moving from top to bottom in a group.
We know that the filling of electrons in an element takes place on different energy levels or shells called as K,L,M,N. As we move left to right in a period, addition of electrons in these shells takes place. While electrons along with protons get added up, the energy level in a particular period remains the same.
This results in the elements that are at the end of the period, to have more number of protons as compared to elements at the starting of the period. These protons are added in the nucleus and will affect the electron cloud. They will exert an inward pull on the electron cloud which will shrink the size of the element. So, the size decreases from left to right in a period.
Hence, this trend of decrease in atomic radii is related to addition of electrons.

Note:
The fact that the energy levels along a period remain constant is of great importance as it affects the size of an atom. While the number of energy levels increases down the group results in the increase in the atomic size.