Writing Electron Configurations

The electronic configuration is the distribution of the electrons around the atom. It details the arrangement of the electron around the nucleus of the atom, which is different for every element in the periodic table. The specific notation predicts the chemical reactions and bonds formed between the atoms. The electron shell surrounds the nucleus of the atom and electrons are arranged along with it. The process of writing electronic configuration starts with the shell number followed by the orbital type where the electrons are arranged. To understand the writing of electronic configuration, it is crucial to understand the concepts of shells, subshells, and orbitals. The electrons are distributed across various energy levels in an atom. 

Electron Shell 

The atoms consist of three subatomic particles: proton, electron, and neutron. The proton is positively charged and the neutron has no charge. They are both located in the atomic centre. The negatively charged electron revolves around the atomic nucleus in paths known as shells or energy levels. Here are some key points:

• The shell closest to the nucleus has the lowest energy level. It is divided into four types which are K, L, M, N etc. The shell with the lowest energy level is termed a K-shell with n = 1. 

• The quantum number for each shell is different. It is referred to as the principal quantum number and holds a maximum number of 32 electrons. 

• The shell with the lowest energy level can hold only 2 electrons. The next energy level holds up to 8 electrons.  

Electron Subshell

 The subshell is the area where the electrons move within a shell and its value is based on the angular momentum quantum number. 

• It consists of four types: s, p, d, and f subshells. Each 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 as per the level of energy and are in the order of s<p<d

• The electrons are distributed as per the azimuthal quantum number and represented by l. The quantum number of the subshell is dependent on the quantum number of the shell. If the principal quantum number of the shell is n= 3, the subshell corresponds to l=0, l=1, and l=2.  

Notation 

The shell and subshell are important for the notation of electronic configuration. The labels for the electronic configuration of an atom consist of the shell (indicated by principal quantum number), subshell (provided by azimuthal quantum number), and a total number of electrons present in the superscript of the subshell. 

Let us understand this by writing the electronic configuration for oxygen.

The atomic number of oxygen is 8 which means it has 8 electrons. Hence the electronic configuration will be represented as 1s22s22p4.

The notation helps how the electrons are distributed around the core of the atom. The filling of the atomic orbital is based on the Aufbau principle, Pauli Exclusion Principle, and Hund’s Rule.  

Ways of writing the electronic configuration 

The electronic configuration of electrons for an atom is written majorly in the following two ways: 

• The first method involves the use of the periodic table as a reference for writing the notation. 

• The second method is an algorithm based method involving electron arrangement in elements. 

The principal quantum number (n) defines the maximum number of electrons present in a shell represented by the formulae of 2n2 where n represents the shell number. Here are the steps for writing the electronic configuration:

• It is important to know the atomic number of the element. The atomic number represents the number of electrons present in the element. 

• Here is a tabulation to help understand the distribution of the electrons in the atom based on the principal quantum number

Here are a few points to remember in terms of shells and subshells:

• Each of the s-sublevel consists of only a maximum of 2 electrons.

• The p-subshell can hold a maximum of only 6 electrons.

• The d-subshell can hold a maximum of 10 electrons.

• The f-sublevel holds a maximum of 14 electrons.

Conclusion  

The electronic configuration of an atom is the distribution of the electrons and how it is arranged in the shell and subshell. The shell consists of electrons that share the same principal quantum number. It describes the pathway of the movement of the electron around the nucleus of an atom. However, a subshell is the pathway of electron movement in a shell, determined by four subshells. The shell starts from the lowest energy level and gradually moves to a higher energy level. The shell with the lowest energy level holds a maximum of 2 electrons followed by 8 electrons in the next energy level. In summary, writing the electronic configuration of an atom requires a thorough understanding of the shell and subshell and the distribution of the electrons.