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Electron Configuration

What Is Electron Configuration

Electron configuration, as the name implies, is the arrangement of electrons of an atom or a molecule in atomic orbitals around the atomic nuclei. Based on the electronic configuration, the chemical reactivity of two substances can be predicted. For instance, what kind of reaction is likely to happen and how strong it will be. It is also helpful in determining the valency of an element.

How To Write Electron Configuration

The electron configuration of an atom follows a standard notation in which all electron-containing atomic subshells are placed in a sequence of their filling order. Along with the alphanumeric notation, the number of electrons present in each subshell is written in superscript.

How To Write Electron Configuration

For instance, the electron configuration of potassium (K) is 1s22s22p63s23p64s1. Here, 1s, 2s, 3s represent the subshells, whereas the superscripts denote the number of electrons present in each of those subshells.

However, the standard notation used for writing the electron arrangements often yields lengthy electron configurations. It mainly occurs for elements having a relatively large atomic number.

In such cases, an abbreviated or condensed notation may be used instead of the standard notation. In the abbreviated notation, the sequence of completely filled subshells that correspond to the electronic configuration of its nearest noble gas is replaced with the symbol of that noble gas in square brackets.

Therefore, the abbreviated electron configuration of potassium (K) can also be written using its nearest noble gas configuration, i.e., argon. The electron configuration of argon is 1s22s22p63s23p6. Therefore, the abbreviated notation of potassium (K) is [Ar]4s1. However, the lengthy electronic configuration of argon can also be written by using its nearest inert neighbor neon, having the electronic configuration 1s22s22p6. So, the abbreviated notation for argon would be [Ne] 3s²3p⁶.

General Rules For Assigning Electrons To Atomic Orbitals

As stated, the number of electrons present in each atomic orbital of every subshell determines the electronic configuration of that particular atom. However, the electrons follow some general rules while entering an orbital.

Aufbau Principle: This principle dictates that electrons will occupy the lower energy orbitals before occupying those with higher energy. The energy level of an orbital is calculated by the sum of the principal (n) and the azimuthal (l) quantum numbers, i.e., n+l. In the case of equal ‘n+l’ value, the orbitals having a lower ‘n’ value are filled first.

According to this principle, electrons enter in the following sequence: 1s < 2s <2p <3s <3p <4s <3d <4p <5s <4d <5p <6s <4f and so on.

Pauli-Exclusion Principle: It states that a maximum of two electrons can fit in an orbital, each having opposite spins.

Hund’s Rule: It states that every orbital in a given subshell is singly occupied by electrons before a second electron is filled. Also, the electrons in the orbitals that contain only one electron all possess the same spin, i.e., the same values of the spin quantum number.

Representation of electronic Configuration of Atom

In this section, the electron configurations of a few elements are discussed:

Electron Configuration of Hydrogen

Hydrogen has atomic number 1. It means an atom of hydrogen contains 1 electron, which will be placed in the s subshell of the first shell.

Therefore, the electron configuration of hydrogen will be 1s1.

Electron Configuration of Oxygen

The atomic number of oxygen is 8. It implies that an oxygen atom has 8 electrons, filled in the following order: 2 ( in K shell) and 6 ( in L shell).

Therefore, the electron configuration of oxygen can be written as 1s2 2s2 2p4 or [He] 2s²2p4.

Electron Configuration of Chlorine

Chlorine has the atomic number 17. Its 17 electrons are distributed in the following manner: 2 (in K shell), 8 ( in L shell), and 7 ( in M shell).

The electron configuration of chlorine can be given as 1s22s22p63s23p5 or as [Ne]3s23p5.

Electron Configurations of Some Elements of the Periodic Table

Electron Configuration of some more elements are shown in the table below:

Electron Configuration

Article was last reviewed on Thursday, December 2, 2021

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