Noble Gases
The group 18 elements, whose completely filled valence shells make them exceptionally unreactive.
Formula / equation
ns² np⁶ (He is 1s²)
Unit
Dimensionless
In depth
Their closed-shell configurations give very high ionisation energies and essentially zero electron affinity, so they exist as monatomic gases with very low boiling points set only by dispersion forces. The heavier members are not truly inert: xenon forms genuine compounds with fluorine and oxygen.
Examples in the real world
Helium in cryogenics and balloons, argon shielding a weld, neon in discharge tubes, and XeF₄ as a real xenon compound.