Question

Among the elements \[{\text{Ca, Mg, P}}\] and \[{\text{Cl}}\] , the order of increasing atomic radii is:
A. \[{\text{Mg < Ca < Cl < P}}\]
B. \[{\text{Cl < P < Mg < Ca}}\]
C. \[{\text{P < Cl < Ca < Mg}}\]
D. \[{\text{Ca < Mg < P < Cl}}\]

Answer 1

Hint: Atomic radius is the distance between the center of the nucleus and the valence shell. Atomic radius is one half the distance between two adjacent atoms in a molecule.

Complete step-by-step answer:
Atomic radius is usually measured in angstrom units as it is very small in size. Due to this small size, it is very difficult to measure the atomic radius.

The chemical symbols \[{\text{Ca, Mg, P}}\] and \[{\text{Cl}}\] represent the elements calcium, magnesium, phosphorus and chlorine respectively.

The elements magnesium, phosphorus and chlorine are present in the third period. The elements magnesium, phosphorus and chlorine are present in the groups IIA, VA and VII A respectively.

Calcium is present in the fourth period. Both magnesium and calcium are alkaline earth metals present in group 2 or IIA. Calcium is placed below magnesium in the group of alkaline earth metals. On moving down the group, the atomic radii increase as additional electron shells are added. Hence, calcium has higher atomic radius than magnesium.

In a period, when you move from left to right, the atomic radii decrease. This is due to an increase in the effective nuclear charge. In the third period, the increasing order of atomic radii of magnesium, phosphorus and chlorine is chlorine < phosphorus < magnesium. Hence, the increasing order of the atomic radii for four elements is \[{\text{Cl < P < Mg < Ca}}\]

Hence, the correct answer is option B.

Note: Atomic radius gives the distance between the center of the nucleus and the outermost electrons/valence electron. Effective nuclear charge is always less than the actual nuclear charge due to shielding of valence electrons by core electrons.