Question

What is the configuration of neutral Mg and Cl?
(a) $Mg:[Ne]3{{s}^{2}};Cl:[Ne]3{{s}^{2}}3{{p}^{5}}$
(b) $Mg:[Ne]3{{s}^{1}};Cl:[Ne]3{{s}^{2}}3{{p}^{5}}$
(c) $Mg:[Ne]3{{s}^{2}};Cl:[Ne]3{{s}^{3}}3{{p}^{4}}$
(d) $Mg:[Ne]3{{s}^{2}};Cl:[Ne]3{{s}^{2}}3{{p}^{6}}$

Answer 1

Magnesium is an s-block element which comes under group 2 and period 3. Chlorine is a p- block element which comes under group 17 and period 3.

Complete step by step answer:
When the electrons are distributed into different shells, subshells and orbitals of an atom then it is called electronic configuration.
There are some rules for filling the orbitals:
(I)- Aufbau principle.
(II)- Pauli exclusion principle
(III)- Hund’s rule of maximum multiplicity.
Magnesium is the element of s-block which comes under group 2.
Its atomic number is 12. So, its configuration will be $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}$
The nearest noble gas to magnesium is neon and its configuration is $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}$
So, the electronic configuration of Magnesium will be $[Ne]3{{s}^{2}}$
Chlorine is the element of p-block and comes under group 17.
Its atomic number is 17. So, its configuration will be $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{5}}$
The nearest noble gas to magnesium is neon and its configuration is $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}$
So, the electronic configuration of Chlorine will be $[Ne]3{{s}^{2}}3{{p}^{5}}$
Hence, the correct answer is an option (a)- $Mg:[Ne]3{{s}^{2}};Cl:[Ne]3{{s}^{2}}3{{p}^{5}}$

Additional information: Aufbau principle: the orbitals are filled according to their increasing energy in the ground state.
The order is: $\text{1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p}.$
Pauli exclusion principle: An orbital can have two electrons at maximum. These electrons must have opposite spin.
Hund’s rule: Pairing of an electron cannot be done in p, d, and f orbital until each subshell contains one electron.

Note: You must always follow the rules before doing any configuration. The series of the orbitals should be correct. When the ionic form of the element is asked the configuration will be changed accordingly.