eguruchela

Electronic configuration

Electronic configuration is defined as the distribution of electrons into various orbitals of an atom by using three principles.

Aufbau principle

In 1920, Danish physicist Niels Bohr formulated this principle, Aufbau principle states that in the ground state of the atoms the orbitals are filled in order of their increasing energies. Electrons first occupy the lowest-energy orbital and then enter into successive higher energy orbitals. The electrons enter into various orbitals in an increasing order of (n+l). As per this 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 etc.

Pauli's Exclusion

Pauli's exclusion principle states that: An orbital can have maximum two electrons with opposite spin. This principal stated that “no two electrons in the same atom have the same values for all four quantum numbers”.

Hund's Rule

Hund's Rule of Maximum Multiplicity states that: Electron pairing in p, d and f orbitals cannot occur until each orbital of a given sub-shell contains one electron each or is singly occupied.

  • We can represent the electronic configuration of atoms in two ways.
  • Orbital diagram method
  • nlx method

    • An electron configuration consists of the symbol for the occupied subshell with a superscript indicating the number of electrons in the subshell.

    The electron configuration for sodium (atomic number 11) is 1s22s22p63s1

  • The large numbers represent the energy level.
  • The letters represent the sublevel.
  • The superscript numbers indicate the number of electrons in the sublevel.

    • Two ways to check an electron configuration:

  • The last notation in the electron configuration represents the location of the element on the periodic table.
    • Example:

    the 3s1 in the electron configuration for sodium above indicates its location as the first square in the s sublevel on the third row of the periodic table.

  • The total of the superscripts in an electron configuration equals the atomic number of the element.
    • Example:

    the total of the superscripts in the electron configuration for sodium above is 11, its atomic number.