Question

Define atomic radius how do the atomic radii of elements vary when we move . 1 down the group. 2 across the period

Answer 1

Answer: atomic radius is defined as the distance from centre of the atom to the outermost shell where electrons are available

Explanation: when we go down the group the electrons are added to different shells because principal quantum number increases (n) therefore radius increases

When we move along the period successive electrons are added to the same shell which increases the attraction by the nucleus hence radius decreases

For example

Lithium is 1s2 2s1

Beryllium is 1s2 2s2 they belong 2nd period you can see that the new electron is added to 2s

Sodium is 1s2 2s2 2p6 3s1 here electron is added to 3s