Question

Which amongst the following elements has the largest atomic radii?
A) Na
B) Mg
C) K
D) Ca

Answer 1

Atomic radii is the distance between the center of the nucleus and the electron in the outermost shell of the atom. It is also defined as the half of the distance between two nuclei of identical atoms bonded by a bond.

Complete answer:
To find out the answer to this problem we’ll first study the properties of the atomic radii in the group and across the period.
The periodic table is designed as per the atomic number of the elements. More the atomic number, the more the electrons get added to the outermost shell. More electrons are added means, the number of orbitals will also increase and the repulsion between the electrons will also increase.
The trend of the atomic radii down the group is: As we move down the group the atomic radii increase because of greater number of electrons and repulsion. As we move across the period, the atomic radii will decrease, as the net attraction of the electrons and the nucleus will increase, which will in turn decrease the size.
Among the given elements, Na, K Ca belongs to group I and Mg belongs to group II of the periodic table. Hence, Mg will have the least atomic radii. As we move down the group the size increases, hence Ca will have the largest size among all. The order of atomic radii can be given as: $Ma < Na < K < Ca$

Hence the correct answer is Option D.

Note:
The expectation of the trend is the Noble Gases Group which is the Group XVIII of the periodic table. Noble gases have the largest atomic radii in any period. This is due to the large no. of electrons in their shell and also the repulsion between atoms. The stable electronic configuration of Noble gases makes it inert.