The atom is the building block of matter that occupies space and has mass. It is the basic unit that consists of protons (positively charged ions), neutrons (neutral) and electrons (negatively charged). The subatomic particles are distributed in the atom differently. The electronic configuration of the atom is the distribution of electrons around an atom. The atomic orbitals exist around the core of the atoms and distribute the electrons. The electron configuration of Hydrogen, oxygen and all other elements helps us in finding out the number of electrons around the atomic orbital. The topic emphasises the electronic configuration representation of atoms.

Difference between shell, subshell and orbital in electron configuration 

Finding the electronic configuration of hydrogen and all other elements in the periodic table requires an understanding of shell, subshell and orbital. 

• The shells are present around the atom’s nucleus and define the energy level. The shell closest to the nucleus has the lowest energy level. The shells are named K, L, M, N, etc. The shell with the lowest energy level is termed as K-shell. The quantum number for each shell is different. The shell can hold a maximum number of 32 electrons. 
• The subshell is the pathway of movement of the electron within a shell. It consists of all the electrons which share the same angular momentum quantum number. The maximum number of electrons held by each of the sub-shell depends on the type. Each shell consists of four types of subshells s, p, d, and f. There are several orbitals present in each subshell. 
• The orbital describes the wave-like behaviour of an electron and hence helps in showing the exact movement of an electron. The number of orbitals present in each subshell varies. The s-subshell consists of 1 orbital, p-subshell consists of 3 orbitals, d-subshell consists of 5 orbitals, and the f-subshell consists of 10-orbital. 

Representation of electronic configurations 

The number of electrons around the core of the atom represents electronic configuration. Each of the elements in the periodic table has a different atomic number and hence has a specific electronic configuration.

Electron Configuration of Hydrogen

• The atomic number of hydrogen is 1 indicating the presence of only one electron.
• The electron in the hydrogen is present in the s-subshell of the first shell.
• The electron configuration of hydrogen is represented by 1s1.

Electronic configuration of oxygen 

• Oxygen elements consist of a total of 8 electrons and hence have an atomic number of 8.
• 1s22s22p4 represents the electronic configuration of oxygen. 
• There are 2 electrons present in the K-shell whereas 6 electrons present in the L-shell

Chlorine electronic configuration 

• The atomic number for chlorine is 17, which means it consists of 17 electrons.
• The chlorine electronic configuration is represented by 1s22s22p63s23p5
• The electrons are distributed in chlorine with 2 electrons in the K shell, 8 electrons in the L shell, and 7 electrons in the M shell. 

Rules that apply for writing the electronic configuration of elements 

The calculation of the electronic configuration of elements follows three basic rules. The rules help in understanding how electrons occupy and fill the atomic orbitals:

• Aufbau’s principle is significant in understanding how electrons fill the atomic orbitals, starting from the lowest energy level or ground state and gradually increasing to a higher energy level. Hence, the electrons occupy the orbitals in increased order of energy level.
• The Pauli Exclusion principle states that no two electrons have the same quantum number. Each orbital consists of a maximum of two electrons in opposite spin directions.
• Hund’s rule shows that all the subshells in the orbital are first singly occupied, followed by being doubly occupied.

Uses and applications of Electronic configuration 

The writing and representation of electronic configuration help in understanding how the electrons are distributed around the atom. There are many applications of electronic configuration.

• It helps in understanding the chemical reactions and how the stabilisation occurs. It helps in calculating or measuring the loss or gain of electrons to form a stable bond.
• The electronic configuration of hydrogen and other elements in the periodic table help determine the valency of an element. The valency of an atom shows the number of electrons present in the outermost shell of an element.
• It helps in predicting the physical and chemical properties of an element in a periodic table and which group it belongs to.
• The electronic configuration is useful for interpreting the atomic spectra. It is useful in finding the atomic orbitals in the ground state or at their lowest energy level.

Conclusion

The electronic configuration of an atom is the number of electrons and their distribution around the atom. The electronic configuration of hydrogen and other periodic table elements is represented by its atomic number which is the number of electrons it consists of. The electronic configuration is determined and explained with the help of three major rules which are the Aufbau principle, Pauli Exclusion principle, and Hund’s rule. The electronic configuration for any elements is written by adding the electrons around each shell and subshell. Each shell can hold a maximum of 32 electrons. The sub-shells are part of the shell consisting of electron numbers depending on their type. The topic provides an insight into the representation of the electronic configuration.