Quantum Numbers and Electron Configurations

Using the Aufbau Principle, determine the electron configuration for the element with atomic number 26.

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Describe how the Pauli Exclusion Principle is applied in the electron configuration of helium.

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Determine the electron configuration for the element with atomic number 15 and explain the reasoning.

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What does the diagram above represent?

• Electrons will occupy the orbitals having lower energies before occupying higher energy orbitals.

• The order in which electrons are filled in atomic orbitals

• This principle is named after the German word ‘Aufbeen’ which means ‘build up’.

• It is important to note that there exist many exceptions to the Aufbau principle

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Aufbau Principle

• According to 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…

• The energy of an orbital is calculated by the sum of the principal and the azimuthal quantum numbers.

• This principle is named after the German word ‘Aufbeen’ which means ‘build up’.

• The Aufbau principle dictates that electrons will occupy the orbitals having lower energies before occupying higher energy orbitals.

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The electron configuration of chlorine is illustrated above. It can be written as

• [Ne]3s²3p⁵

• 1s²2s²2p⁶3s²

• 1s²2s²2p⁶3s²3p⁵

• [He]3s²3p⁵

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The Pauli exclusion principle states that a maximum of ____ electrons, each having opposite spins, can fit in an orbital.

Pauli Exclusion Principle

• This rule describes the order in which electrons are filled in all the orbitals belonging to a subshell.

• This principle can also be stated as “no two electrons in the same atom have the same values for all four quantum numbers”.

• The Pauli exclusion principle states that a maximum of two electrons, each having opposite spins, can fit in an orbital.

• The Pauli exclusion principle states that a maximum of two electrons, each having opposite spins, can fit in an orbital.

Chlorine has an atomic number of 17. Therefore, its 17 electrons are distributed in the following manner:

• K shell – 1 electrons

  L shell – 8 electrons

  M shell – 7 electrons

• K shell – 2 electrons

  L shell – 7 electrons

  M shell – 7 electrons

• K shell – 2 electrons

  L shell – 8 electrons

  M shell – 6 electrons

• K shell – 2 electrons

  L shell – 8 electrons

  M shell – 7 electrons

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