Question

Electronic configuration of Radium is?
a.) [Rn]$6{s^2}$
b.) [Rn] $7{s^2}$
c.) [Rn] $5{s^2}$
d.) [Rn] $6{s^1}$

Answer 1

Hint: The radium is the element from the 7th period and group 2. The group 1 and 2 involves the filling of s orbital while the 7th period indicates the filling of 7th shell. This element belongs to the beryllium family. So, it will have an electronic configuration similar to beryllium only with the difference in the outer shell only.

Complete step by step solution:
Let us know what electronic configuration is first.
The electronic configuration may be defined as the distribution of electrons of an atom or molecule in the atomic or molecular orbitals.
The electrons are filled on the basis of the Aufbau principle. It states that the electrons should be filled in atomic orbitals from lowest energy level to the higher ones.
The filling of electrons in atomic orbitals will give electronic configuration of radium as-
$1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^{10}}4{s^2}4{p^6}4{d^{10}}5{s^2}5{p^6}4{f^{14}}5{d^{10}}6{s^2}6{p^6}7{s^2}$
Writing the electronic configuration of higher elements like this is a tedious process. So, we write the name of nearest noble gas and then the electronic configuration of valence electrons.
The nearest noble gas to radium is radon which is written as- Rn.
The electronic configuration of radium this way can be written as- [Rn] $7{s^2}$

So, the option (B) is the correct answer.

Note: The easiest way to predict from above options is as-
We know that Radium belongs to the 7th period. So, the valence electrons of radium will be in the 7th shell only. Further, we know that it belongs to alkaline earth metals. So, in that case, s- orbital will be filled only and the s orbital can occupy a maximum of two electrons.