Electron Configuration: Aufbau, Pauli Exclusion Principle & Hund’s Rule

Electron Configuration is the distribution of electrons where they are found i.e. Atoms or Ions and one of the best ways to figure out is by looking at the ionization energy. The electrons are arranged in shells, subshells, and orbitals, those on the inside are called core electrons and the ones outside are referred to as valence electrons.

So if you were to write the Electron Configuration of Zinc (atomic number = 30) it will be 1s²2s²2p⁶3s²3p⁶3d¹⁰4s² .

However, writing such lengthy notation is time consuming and sometimes becomes difficult to understand. So another way of writing this is by using the condensed or abbreviated form which includes replacing the completely filled subshells with that of the noble gases. So the Electron Configuration of Zinc can be written as [Ar]3d¹⁰4s².

Electron Configurations Uses

• It is used to determining the valency of an element.
• When you want to predict the properties of a group of elements.
• Electron Configuration is useful in interpreting atomic spectra.
• Describing the atomic orbitals in their ground state.

How To Write Electron Configurations?

Before knowing how to write the Electron configuration you must know the concepts of Shells, Subshells, and Notation.

Shells

The shell of an electron is the outer part around the nucleus of an atom. Shell number is denoted by “n” & the max no. of electrons that can be accommodated in a shell is based on the principal quantum number. We have listed the value of n, shells, and the max number of electrons that can be accommodated below:

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Subshells

These are a group of orbitals that share the same principal quantum number & azimuthal quantum numbers (l). There are 4 subshells – s, p, d, and f & each can hold different numbers of electrons. The number of subshells that complete a shell is determined by “n”.

Max No. Of Electrons Accommodated By Subshell = 2*(2l + 1)

So the maximum no. of electrons that can be accommodated by s, p, d, and f subshells are 2, 6, 10, and 14, respectively.

The possible values on n for subshells up to 4 are given below:

So it can be concluded that the value of the azimuthal quantum number (l) is always less than that of the principal quantum number (n) therefore 1p, 2d, and 3f orbitals do not exist.

Notation

• a) For an atom the electron configuration is written using subshell labels.
• b) The labels have the shell number (provided principal quantum number), the subshell name (provided azimuthal quantum number) and the total number of electrons in the subshell.
• c) Eg if two electrons are filled in the ‘s’ subshell of the first shell, the notation will be ‘1s²’.
• d) With the help of these subshell labels, the electron configuration can be written as 1s²2s²2p⁶3s²3p⁶4s²3d⁶.

How To Fill Atomic Orbitals?

There are 3 methods for filling the atomic orbitals

• 1. Aufbau Principle
• 2. Pauli Exclusion Principle
• 3. Hund’s Rule

Aufbau Principle

According to the Aufbau Principle in NCERT Book “In the ground state of the atoms, the orbitals are filled in order of their increasing energies“. You can calculate the orbital energy by the sum of azimuthal and the principal quantum number. As per the principle electrons are filled in the following order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p and so on. Let you provide you with a better explanation using figure:

Pauli Exclusion Principle

Wolfgang Ernst Pauli was a pioneer in quantum physics from Australia according to his principle “Only two electrons may exist in the same orbital and these electrons must have opposite spin” or “No two electrons in an atom can have the same set of four quantum numbers“.

The above means that 2 electrons can have the same value of n, l, and m (3 quantum numbers) but must have the opposite spin quantum number. This helps in calculating the capacity of electrons present in any subshell.

Also, the maximum number of electrons in the shell with principal quantum number n is equal to 1n².

Hund’s Rule Of Maximum Multiplicity

Hund’s rule deals with the filling of the e^– in orbitals that belong to the same subshell. According to the rule “pairing of electrons in the orbitals belonging to the same subshell (p, d or f) does not take place until each orbital belonging to that subshell has got one electron each i.e., it is singly occupied“.

Example: Nitrogen atoms with atomic number Z=7 have Electronic Configuration 1s²2s²2p³.

Electron Configuration Of Elements

In the next few sections, we will provide the e^– configuration of elements like chlorine, hydrogen and oxygen that will help in clearing the concepts a bit more.

Electron Configuration of Chlorine

The atomic number of Chlorine is 17 and its 17 electrons are distributed as:

The electron configuration of chlorine is written as 1s²2s²2p⁶3s²3p⁵ or as [Ne]3s²3p⁵.

Electron Configuration of Hydrogen

Hydrogen has atomic number 1 therefore its electron configuration will be 1s¹.

Electron Configuration of Oxygen

With atomic number 8, the oxygen holds 8 atoms in its shells the electron configuration is written as – 1s² 2s² 2p⁴.

Electron Configuration Table

Students can check the periodic table representing electron configuration below:

FAQs & Problems On Electron Configuration

Solving the below question will help you in building the concepts and knowing more about Electron Configuration.

That was all the information on Electron Configuration, we hope the information provided on this page was helpful. However, if you have further questions feel to use the comments section.