Noble gases earned their regal name because they were considered too "noble" to react with common elements — and for decades, chemists believed they were completely inert. Helium, neon, argon, krypton, xenon, and radon sit in Group 18 with their electron shells full to the brim: helium has a complete 1s² shell, while the others have full s²p⁶ outer shells. With no need to gain, lose, or share electrons, they exist as single atoms floating contentedly through the air. Argon alone makes up 0.93% of Earth's atmosphere — about 65 trillion tonnes of a gas most people have never heard of, surrounding us all the time.
The notion that noble gases never react was shattered in 1962 when Neil Bartlett synthesized xenon hexafluoroplatinate, proving that at least the heavier noble gases could form compounds under the right conditions. Since then, dozens of xenon and krypton compounds have been made, though none occur naturally. Helium remains stubbornly unreactive — no stable helium compound has ever been created under normal conditions. This chemical inertness is precisely what makes noble gases so useful: argon provides an inert atmosphere for welding and growing silicon crystals, helium cools MRI magnets to superconducting temperatures (4.2 K, or -269°C), and xenon fills high-performance car headlights and satellite ion thrusters.
Neon signs gave an entire era of American culture its glow, though most "neon" signs actually use other gases — true neon produces only a characteristic red-orange light. Krypton-86 once defined the meter before lasers took over. Radon, the only radioactive noble gas, seeps naturally from uranium-bearing rocks and is the second leading cause of lung cancer after smoking, prompting radon testing in homes worldwide. Helium is also irreplaceable and increasingly scarce — it is produced mainly by radioactive decay underground and, once released, escapes Earth's gravity forever.