Question

How does atomic radius vary in a period and in a group? How do you explain the variation?

Answer 1

As we go left to right across period atomic radius goes on decreasing because the outermost e- goes in 2p subshell
so nuclear charge increases therefore the outermost electrons held tightly to the nucleus
so atomic radius decreases as we move down from top to bottom across group theatomic radius increases

Answer 2

Answer:

Atomic radius declines as we move from left to right in a period. It happens because in a period, the external electrons are available in a similar valence shell so, the atomic number increments from left to right in a period, which results in increase in the effective nuclear charge. Therefore, the attraction of electrons towards the nucleus is increased.

Also, atomic radius declines as we move from top to bottom in the group. It happens because as we move down in a group then there is increase in  principal quantum number(n) which brings about increase in the  distance between nucleus and the valence electrons.