Noble Gas Core Definition

A noble gas core is an abbreviation in an atom's electron configuration where the previous noble gas's electron configuration is replaced with the noble gas's element symbol in brackets. Writing an electron configuration using the noble gas core can save you a lot of time!

Examples

Sodium has an electron configuration of:

1s²2s²p⁶3s¹

The previous noble gas on the periodic table is neon with an electron configuration of:

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Alphabetical Electron Configuration List of Elements

By Anne Marie Helmenstine, Ph.D.

1s²2s²p⁶

If this configuration is replaced by [Ne] in sodium's electron configuration it becomes:

[Ne]3s¹

This is the noble gas core notation of sodium.

With a more complex configuration, the noble gas core becomes even more helpful. Iodine (I) has a standard electron configuration of:

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁵

The noble gas prior to iodine on the periodic table is krypton (Kr), which has the electron configuration:

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶

This is the noble gas core for iodine, so the shorthand notation for its electron configuration becomes:

[Kr]5s²4d¹⁰5p⁵