Question

Write the electronic configuration of Beryllium?

Answer 1

Hint: To express the electrical configuration of a specific element, we must first determine its atomic number. The dispersion of electrons in an element’s atom into distinct shells and subshells is known as electronic configuration. Knowing the atomic number tells us how many electrons should be distributed among the orbitals. Before writing the electrical configuration of an atom, a series of rules must be observed.

Complete 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 the principal quantum number (n). The maximum number of electrons that can be accommodated in a shell is calculated by the formula \[2{n^2}\] which 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 \[l = 0,l = 1,l = 2,andl = 3\] and are named the s, p, d, and f subshells, respectively. The maximum number of electrons that a subshell can accommodate 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 the lowest energy term for a given electron configuration is the one with the greatest value of spin multiplicity. This implies that electrons will occupy them singly before filling them in pairs if two or more orbitals of equal energy are available.
Since the atomic number of beryllium is 4 therefore 4 electrons are to be distributed in the electronic configuration as: \[1{s^2}2{s^2}\]

Note:
We must note 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 exceptions to 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 which block the element belongs to.