Question

Among the elements $Ca,Mg,P$ and $Cl$, the order of increasing atomic radii is:

• A. $Mg<Ca<Cl<P$
• B. $Cl<P<Mg<Ca$
• C. $P<Cl<Ca<Mg$
• D. $Ca<Mg<P<Cl$

Answer 1

Answer: (B)

$Cl<P<Mg<Ca$

Atomic radii increases, as the number of shells increases. Thus, on moving down a group atomic radii increases.
The electronic configuration of the given element is:
$M{g}_{12}=\left[Ne\right]3s^2$
$C{a}_{20}=\left[Ar\right]4s^2$
$P_{15}=\left[Ne\right]3s^{2}3p^3$
$C{l}_{17}=\left[Ne\right]3s^{2}3p^5$
On the other hand, on increasing the number of electron in the same shell, the atomic radii decreases because effective nuclear charge is increases.
In $Mg,P$ and $Cl$, the number of electrons are increasing in the same shell, thus the order of their atomic radii is
$Cl<P<Mg$
In case of $Ca$, the electron is entering in higher shell. So, its atomic radii is highest.
Thus, the order of radii is $Cl<P<Mg<Ca$