Electronic configuration is an essential concept in chemistry and understanding chemical equations. Each atom consists of three subatomic particles – electron, proton, and neutron. The positively charged proton and chargeless neutron are concentrated in the atom’s core. The electron is negatively charged and distributed around the atom. The electronic configuration is the pattern in which electrons are distributed around the atom in atomic orbitals. Writing electron configurations requires following a few rules and foundation knowledge of shell, sub-shell, and orbitals. The following discusses the representation of the electronic configuration of an atom.  

Arrangement of Electrons Around Atomic Orbitals  

Electrons, arranged around an atom in orbitals, are called the electronic configuration. Electrons start occupying the lowest energy level or from the ground state and gradually occupy increasing energy levels, writing electron configurations. As the electron occupies the higher energy level, it possesses more energy and hence has more distance from the nucleus.

• The shell provides the pathway followed by electrons around the nucleus of an atom. It is determined by principal quantum energy. 
• The subshell area where electrons move within a shell and its value are based on the angular momentum quantum number. 

Further, is the standard notation for writing electronic configurations. The sequence of electrons fills the subshells in a step by step manner. Following is the note for filling atomic orbitals: 

For example, when writing the electronic configuration of hydrogen. 

It has an atomic number of 1, meaning it consists of one electron. The representation of the electronic configuration of the atom is:

 = 1s¹.

Where the normal 1 = energy level.

S = type of orbital.

Superscript 1 = number of electrons in the orbital. 

Importance of Using Electronic Configuration 

The concept is crucial in identifying and understanding the arrangement of the electrons around an atom. Here is the importance of using the electronic configuration:

• It helps determine the element’s valency. The valency is the number of electrons located in the outermost orbital.  
• The electronic configuration determines the chemical behaviour of an element. When the outermost shell fills, it is chemically unreactive, like in the case of halogen. However, when an element consists of less than 8 electrons, it is reactive and stabilises the gaining electron. 
• The electronic configuration provides atomic spectra interpretation.  

Writing Electron Configurations

There are three central rules followed while writing electronic configuration for elements. It involves understanding the shell and subshell and distribution of electrons around the atom. 

Shells define the pathway followed by the electrons around the atom. The maximum electrons accommodated in a shell are based on the principle quantum number with a value of n. The formulae for presenting the number of electrons in the shell is 2n².

• Subshells are present in shells, and each of the subshells, the electrons, is distributed based on the azimuthal quantum number. 
• It consists of four types consisting of the s, p, d, and f subshell. Each of the subshells consists of several orbitals. 
• S-subshell consists of 1 orbital with a maximum of 2 electrons, p-subshell consists of 3 orbitals with a maximum of 6 electrons, d-subshell consists of 5 orbitals with a maximum of 10 electrons, and f-subshell consists of 7 orbitals with a maximum of 14 electrons. 
• The subshells are arranged per the energy level and are in the order of s<p<d<f. 
• The formulae for the electron arrangement in the subshell are provided by the formulae of 2 x (2l +1).

Filling of The Atomic Orbitals

The notation of electronic configuration and how it fills the orbital is based on the three essential rules. 

The filling of atomic orbitals is based on the following: 

• The Aufbau principle states that the electrons first occupy the orbitals, which have lower energy levels, followed by occupying higher energy orbitals. The sum of the principal and azimuthal quantum numbers provides the energy of an orbital. 
• The Pauli Exclusion principle is an important rule, which states that a maximum of only two electrons can fit the orbital, each with an opposite spin. Also, no two electrons consist of the same quantum number value. 
• According to Hund’s rule, the electrons are filled in the orbital. Initially, each subshell is occupied by a single electron before being filled with a second electron. 

Conclusion  

The electronic configuration of an atom identifies the arrangement or distribution of the surrounding electrons. However, writing electron configurations requires knowledge of the shell around the atom and the subshell number. It helps identify the valency of the atom, meaning the number of electrons in the outermost shell. The filling of atomic orbitals is based on three rules explaining how electrons fill the orbitals around the atom. In summary, the combination of Aufbau’s principle, Pauli Exclusion principle, and Hund’s rule help calculate the distribution of the electrons and how it fills the atomic orbitals.