Noble Gas Rule
The noble gases are, for all intents and purposes, chemically inert - that is that they do not react. Examination of their electronic configurations reveals that, except for helium, they all have the filled s and p orbitals, i.e., ns2np6. This observation suggests that we can attribute their lack of chemical reactivity to this filled s and p electronic configuration.
Noble Gas Electronic Configurations 
Noble Gas Electronic congifuration
He  1s2 
Ne [He]2s2 2p6
Ar  [Ne]3s2 3p6
Kr [Ar]3d10 4s2 4p6
Xe  [Kr]4d10 5s2 5p6
Rn [Xe]4f14 5d10 6s2 6p67
The lesson we take away from this observation is that the ns2np6 electronic configuration is very stable. We can expect that any element or ion that is isoelectronic with a noble gas will also be stable. This observation is known as the noble gas or "octet" rule.

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C101 Class Notes
Prof. N. De Leon