Noble Gas Configuration – Shorthand Electron Configuration

In chemistry, the noble gas configuration is a shorthand method of writing an atom’s electron configuration. The reason for using the noble gas configuration is because the full electron configuration becomes very long for atoms with high atomic numbers.

Here is a look at how to write a noble gas configuration and a list of the electron configurations for all 118 elements.

How to Write a Noble Gas Configuration

The noble gas configuration gives the noble gas core that occurs before the element on the periodic table and then the electron configuration of the atom’s valence electrons. But, you need to understand how to write the full electron configuration to find the number of valence electrons.

Here are the steps for writing a noble gas configuration:

1. Find the number of electrons for the atom. For a neutral atom, this is the same as the atomic number. (For an ion, the number of electrons is not the same as the number of protons, but otherwise the same steps apply.)
   
   
2. Fill in the electron shells and energy levels with the electrons.
   
   Each s shell holds up to 2 electrons.
   Each p shell holds up to 6 electrons.
   Each d shell holds up to 10 electrons.
   Each f shell holds up to 14 electrons.
   
   
3. Follow the Aufbau rule and write the full electron configuration. The Aufbau principle states that electrons fill lower energy levels before adding to higher energy levels. While you can use brute force to write the configuration, it’s easier to draw a diagram and follow the diagonal:
   
   1s
   2s 2p
   3s 3p 3d
   4s 4p 4d 4f
   5s 5p 5d 5f
   6s 6p 6d
   7s 7p
   8s
   
   Notice the orbits overlap, so you don’t just fill the shells sequentially (1, 2, 3, 4, …). Instead, use Madelung’s rule:
   
   1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s < 5f < 6d < 7p
   
   Note: Madelung’s rule is not a hard-and-fast rule, especially where some of the heavier transition metals are concerned. Relativistic effects come into play and change the order.
   
4. Find the noble gas preceding the element on the periodic table. Write the noble gas configuration by writing the noble gas core, followed by the valence electrons. A noble gas core is the noble gas element symbol enclosed in brackets: [He], [Ne], [Ar], [Kr], [Xe], or [Rn]. The valence electrons are “leftover” electrons that don’t fill a shell or satisfy the octet rule (except for noble gases) or 18-electron rule (transition metals). There are two easy ways to identify them. Valence electrons are the electrons leftover past the noble gas electron configuration. They are also characteristic of an element group. For example, the alkali metals always have 1 valence electron.

Noble Gas Configuration Examples

For example, write the noble gas configuration of sodium.

• The atomic number of sodium is 11, so you know the neutral atom has 11 protons and also 11 electrons.
• Filling in the electron shells using the Aufbau principle gives a configuration of 1s² 2s² sp⁶ 3s¹. Add up the superscripts and double-check to make sure you have the correct number of electrons.
• Write the noble gas configuration. Looking at a periodic table, note the noble gas before sodium is neon. The electron configuration of neon is 1s² 2s² 2p⁶. So, the noble gas core symbol [Ne] replaces that portion of the sodium electron configuration. The noble gas configuration for sodium is [Ne] 3s¹.

For example, write the noble gas configuration of neon.

• Neon is a noble gas, but you can do better than just write [Ne] and call it good. First, use the periodic table and see the number of electrons for a neon atom is 10.
• Follow the Aufbau principle and fill electron shells: 1s² 2s² 2p⁶
• Write the noble gas configuration using the noble gas core before neon on the periodic table, followed by the valence electrons. The noble gas configuration of neon is [He] 2s² 2p⁶. Notice the valence of neon is 8 (2 electrons in the 2s shell and 6 electrons in the 2p shell), which indicates it has a filled octet.

List of Noble Gas Configurations for All 118 Elements

References

• Dzikowski, K. D.; et al. (2021). “Relativistic effective charge model of a multi-electron atom”. Journal of Physics B: Atomic, Molecular and Optical Physics 54 (11): 115002. doi:10.1088/1361-6455/abdaca
• Langmuir, Irving (June 1919). “The Arrangement of Electrons in Atoms and Molecules”. Journal of the American Chemical Society. 41 (6): 868–934. doi:10.1021/ja02227a002
• Rayner-Canham, Geoff; Overton, Tina (2014). Descriptive Inorganic Chemistry (6th ed.). Macmillan Education. ISBN 978-1-319-15411-0.
• Stoner, E.C. (1924). “The distribution of electrons among atomic levels”. Philosophical Magazine. 6th Series. 48 (286): 719–36. doi:10.1080/14786442408634535
• Wong, D. Pan (1979). “Theoretical justification of Madelung’s rule”. Journal of Chemical Education. 56 (11): 714–18. doi:10.1021/ed056p714