Noble gas
Group 18 elements with full valence shells and low reactivity.
The noble gases, historically called inert gases or aerogens, are the members of group 18 of the periodic table: helium, neon, argon, krypton, xenon, radon, and in some cases oganesson. Under standard conditions, the first six are odorless, colorless, monatomic gases with very low chemical reactivity and cryogenic boiling points. Their inertness results from a full outer shell of valence electrons, giving them little tendency to participate in chemical reactions. The noble gases are useful whenever chemical reactions are unwanted, such as argon as a shielding gas in welding and helium for buoyancy in blimps.
- group
- Group 18 of the periodic table
- members
- Helium, neon, argon, krypton, xenon, radon, oganesson
- key_property
- Very low chemical reactivity due to full valence electron shell
Reader's Guide
The discovery of the noble gases was unique in the history of chemistry, as an entirely new group of elements with no previously known representative. Oganesson, the seventh member, is an unstable synthetic element with uncertain chemistry; only five very short-lived atoms have been synthesized as of 2020. Their industrial quantities, except radon, are obtained from air via liquefaction and fractional distillation; helium is also a byproduct of natural gas mining. Radon is isolated from radioactive decay of radium, thorium, or uranium compounds.
Did You Know?
- Argon forms about 0.94% by volume of Earth's atmosphere due to decay of radioactive potassium-40.
- Helium is the only element that cannot be solidified by cooling at atmospheric pressure; a pressure of 25 standard atmospheres at 0.95 K is required.
Frequently Asked Questions
What is Noble gas in the periodic table?
Noble gas refers to the seven elements occupying Group 18: helium, neon, argon, krypton, xenon, radon, and oganesson. They are all monatomic, colorless, and odorless under normal conditions, with cryogenic boiling points that keep them gaseous at everyday temperatures.
Why is Noble gas so chemically unreactive?
Each noble gas atom carries a completely filled outer valence shell, which means it has essentially no thermodynamic drive to gain, lose, or share electrons. This electronic saturation is what makes them historically nicknamed the 'inert' or 'aerogen' gases.
Where does Noble gas show up in everyday technology?
Argon serves as a protective shielding gas in arc welding to prevent the molten metal from oxidizing, while helium's extreme lightness makes it the go-to lifting gas for balloons and airships. Xenon's high polarizability also powers the bright, short-lived flashes inside camera and cinema strobe lamps.
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