By Eric Bank, MBA, MS Finance, Updated March 24, 2022
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The periodic table’s right‑most column houses the noble gases—helium, neon, argon, krypton, xenon, and radon. These elements are gaseous, colorless, odorless, and remarkably unreactive under normal conditions. Their chemical inertness stems from a complete valence shell: all outer orbitals are fully occupied.
Each element is defined by the number of protons in its nucleus and the corresponding number of electrons that orbit it. Quantum mechanics describes these electron positions as shells, subshells, and orbitals. The smallest orbital, the 1s, can host two electrons; the next set, the p orbitals, can hold up to six.
Helium, the lightest noble gas, contains only two electrons that fill its 1s orbital. Every other noble gas has a filled s and a filled p subshell in its outermost shell. This arrangement—two s electrons plus six p electrons—completes the octet rule, giving each noble gas a closed valence shell.
A filled valence shell means the atom has no tendency to gain or lose electrons, rendering it chemically inert. That’s why noble gases are referred to as “noble” and remain largely unreactive with other elements.
