Electron Configuration

The atomic dimensions increase in groups? Significant increases in proton attractive force are occurring, so yes, collective proton charge is also increasing...but so too are the ______________________ among the very crowded electrons. There is an increasing DISTANCE from the nucleus to the farthest flung electrons, effectively diminishing that proton attractive force. The repulsive forces therefore take over, the electrons spread out as much as possible, and to accommodate this the atomic dimension also expands!

• repulsive forces

• attractive forces

Electron Configurations are useful for?

• Determining the number of neutrons in the nucleus

• Determining the number of electrons in the atomic structure

• Determining the number of protons in the nucleus

• Determining the valency of an element.

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

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

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

• Aufbau Principle

• Hund’s Rule

• Pauli Exclusion Principle

• Electron Configuration Rule

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.

Hund’s Rule

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

• 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…

• It states that every orbital in a given subshell is singly occupied by electrons before a second electron is filled in an orbital.

• In order to maximize the total spin, the electrons in the orbitals that only contain one electron all have the same spin (or the same values of the spin quantum number).

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.

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

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

• [Ne]3s²3p⁵

• 1s²2s²2p⁶3s²

• 1s²2s²2p⁶3s²3p⁵

• [He]3s²3p⁵