Question

atomic reason decrease down the group

Answer 1

Why do atomic radius increases as we go down in the group?

Atomic radii of elements gradually increases in a group from top to bottom. As we go down a group, the atomic number increases, thus, the number of shells increases. Also, as we move down the group, the valence electrons are present in a higher shell and thus, the distance of valence electrons from the nucleus increases. As a result of this, the force of attraction between the nucleus and the valence electron decreases. Therefore, the atomic radius increases on moving down a group.

Answer 2

In general, atomic radius decreases across a period and increases down a group. 

Across a period, effective nuclear charge increases as electron shielding remains constant. A higher effective nuclear charge causes greater attractions to the electrons, pulling the electron cloud closer to the nucleus which results in a smaller atomic radius.

Down a group, the number of energy levels (n) increases, so there is a greater distance between the nucleus and the outermost orbital. This results in a larger atomic radius.