Question

The electronic configuration of Fluorine is:

Answer 1

We must know the atomic number of the given element in order to write its electronic configuration. Electronic configuration is the distribution of electrons of the atom of an element into various shells and subshells. Knowing the atomic number tells us the number of electrons which are to be distributed among the orbitals. There are a set of rules which are to be followed before writing the electronic configuration of an atom.

Complete step by step answer:
The following must be kept in mind before writing any electronic configuration.
Principal Quantum number: Electrons in an atom are characterized by a set of four quantum numbers and the maximum number of electrons that can be accommodated in a shell (energy level) is based on principal quantum number (n). The maximum number of electrons that can be accommodated in a shell is calculated by the formula $2{n^2}$ where n is the shell number. When n=1, the maximum number of electrons that can be accommodated are$2 \times {\left( 1 \right)^2} = 2$ .
Azimuthal quantum number: The subshells into which electrons are distributed are based on the azimuthal quantum number, denoted by ‘l’. When $n = 4$ the subshells correspond to $l = 0,$ $l = 1,$ $l = 2,$ and $l = 3$and are named the s, p, d, and f subshells respectively. The maximum number of electrons that can be accommodated by a subshell is given by the formula $2 \times \left( {2l + 1} \right)$ . So s, p, d and f subshells can accommodate $2,6,10$ and $14$ electrons respectively. If two electrons are filled in the ‘s’ subshell of the first shell, the electronic configuration is noted as $1{s^2}$.
Aufbau principle: The Aufbau principle states that in the ground state of an atom or ion, electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels. For example, the 1s subshell is filled before the 2s subshell is occupied.
Pauli’s exclusion principle: This principle states “no two electrons in the same atom have the same values for all four quantum numbers”.
Hund’s Rule of maximum multiplicity: The rule states that for a given electron configuration, the lowest energy term is the one with the greatest value of spin multiplicity. This implies that if two or more orbitals of equal energy are available, electrons will occupy them singly before filling them in pairs.
Since the atomic number of fluorine is 9 therefore there are 9 electrons which are to be distributed in the electronic configuration as: $1{s^2}2{s^2}2{p^5}$ .

Note:
It must be noted that the Aufbau (build-up) principle and the electronic configuration of atoms provide a theoretical foundation for the periodic classification into s-block, p-block, d-block and f-block elements. Also, there are exceptional electronic configurations of Cu, Cr, etc. This is because Fully-filled orbitals and half-filled orbitals have extra stability. Also, while obeying the Aufbau principle, the highest orbital to which the electron enters gives the categorization of to which block the element belongs.