Noble Gas Core Definition

The outer electron shell is filled for a noble gas atom.
The outer electron shell is filled for a noble gas atom. pslawinski, wikipedia.org

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:

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