Question

What is electron configuration of $MO^ { 3+ }$?

Answer 1

To solve the given question, the concepts to be cleared are about Quantum number, shells, sub-shells, orbitals, Pauli Exclusion Principle, Aufbau Rule and P fund's Rule.
Quantum number is basically the address of an electron in an atom.Shells are the permitted orbits where an electron revolves with fixed angular momentum. Subshell is a division under shell which contains orbital or orbitals.

Complete step by step solution:
Step-1:
The atomic number of Molybdenum is $42$. So, the total number of electrons in $MO$ is $42$.
Step-2:
The four quantum numbers are Principal Quantum Number which denotes the shell, Azimuthal Quantum Number denoting sub-shell, Magnetic Quantum Number and Spin Magnetic Number.
The sub-shells are s,p,d,f, . . . . . . They are filled on the basis of energy with the $n + l$ rule.
Step-3:
So, electronic configuration of $MO$ is $1s^22s^22p^63s^23p^63d^{10}4s^24p^64d^4 5s^2$.
Removing $3e^-$ from outer most shell gives $MO^{ 3+ }$. $1s^2 2s^2 2p^6 3s^2 3p^6 3d^{ 10 } 4s^2 4p^6 4d^3$ .

Additional Information:
Pauli’s Exclusion Principle states that any $2$ electron can never have all the same $4$ quantum numbers.
Aufbau Rule explains the filling of electrons according to energy level.
P fund’s Rule explains that every orbital with one electron then fills another electron.
The magnetic quantum number differentiates orbitals in a given subshell. The l is always less than shell when $l=0,s;l=1,p;l=2,d;l=3,f;$ and so on.
$2$ electrons are present in s, $6$ in p, $10$ in d and $14$ in f.

Note:
During the electronic configuration, always make sure to write with inner to outer shells but fill the electron according to energy. The energy of $3d$ is more than $4s$ but $3d$ is written inner to $4s$ .