What is Electron Configuration Simple Definition?

What is Electron Configuration Simple Definition?

Electronic Configuration

It is the systemic distribution of electrons in various energy levels in the order of increasing energy.

The electrons in the various energy levels, sub-energy levels and orbitals are distributed according to the Aufbau principle.

  1. Aufbau principle

It is the process of filling electrons into various energy levels in the order of increasing energy.

The relative energy of various energy levels can be determined by using the following rules.

aufbau principle
  1. ( n+ l ) Rule

According to ( n+ l ) Rule

  1. A sub-shell with the lowest ( n+ l ) value has the lowest energy and is filled first with electrons.
  2. When two or more subshells have the same ( n+ l ) value, then the subshell with a lower value of ‘n’ has the lowest energy and is filled first.

For example consider ( n+ l )values for 3d,4p and 5s orbitals.

For 3d subshell n=3 , l=2 and ( n+ l ) = 3+2 =5

For 4p subshell n=4 , l=1 and ( n+ l ) = 4+1 =5

For 5s subshell n=5 , l=0 and ( n+ l ) = 5+0 =5

All the subshells have the same ( n+ l ) values.

Comparing n- values, the order of filling of the three subshells is :


b)Relative stability of Configuration

Generally, the decreasing order of stability of orbitals with various configurations is:

Completely filled > Empty > Half –filled >Partially filled

  • Hund’s Rule of Maximum Spin Multiplicity

According to Hund’s rule

“When several equal energy ( degenerate ) orbitals are available, an electron prefers to enter an empty orbital rather than entering a half-fiiled orbital and has paired spin”.

The pairing of two negatively charged electrons causes repulsion and energy are required to pair the repelling electrons. This energy is stored in the system and makes it unstable. Thus electrons always try to enter empty orbitals to avoid repulsion and become stable.

  • Pauli’s Exclusive Principle

According to Pauli’s exclusive principle

“ An orbital can contain a maximum of two electrons with opposite spins”.


“Two electrons in the same orbital has always the same values of Principle, Azimuthal and magnetic quantum number but the different value of spin quantum number”.

Two electrons with opposite spins in an orbital are called paired electrons and the orbital is called a completely filled orbital.

A single electron in an orbital is called an unpaired electron and an orbital is called a half-fiiled orbital. The orbital with opposite spins of two electrons has lower energy and is more stable.

Electronic Configuration of Iron

Electronic Configuration of Iron

Uses for electron configurations include:

  • Figuring out an element’s valency.
  • Predicting a set of components’ qualities (elements with similar electron configurations tend to share similar properties).
  • Analysis of atomic spectra


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