Noble Gas Core Definition

close up of sodium on periodic table

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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!


Sodium has an electron configuration of:


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


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


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:


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


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