What periodic trends do we observe in terms of atomic radii

What periodic trends do we observe in

terms of atomic radii or atomic sizes in Modern periodic table?

Answer: Following two trends are observed. 

1. Within each column (group), atomic radius tends to increase from top to bottom. This trend results primarily from the increase in the number of the

outer electrons. As we go down a column, the outer electrons have a greater probability of being farther

from the nucleus, causing the atom to increase in size. 

2. Within each row (period), atomic radius tends to decrease from left to right. The major factor influencing this trend is the increase in the nuclear charge as we move across a row. The increasing

effective nuclear charge steadily draws the valence electrons closer to the nucleus, causing the atomic radius to decrease.