Noble gases

The noble gases are a group of elements occupying Group 18 (the far-right column) of the periodic table. This family consists of seven elements: helium, neon, argon, krypton, xenon, radon, and the recently discovered oganesson. They are often called “inert gases” (or “rare gases”) because of their striking lack of chemical reactivity – in fact, they are the least reactive elements known. The atoms of noble gases have full valence electron shells, which means they have little tendency to gain or lose electrons or to form chemical bonds. This complete outer shell is the secret to their standoffish behavior: under normal conditions, noble gases do not readily react with other elements, earning them the moniker “noble” for their aloofness (by analogy to nobility not mingling with commoners).

In terms of physical properties, all noble gases (except perhaps oganesson) are colorless, odorless, monatomic gases at room temperature. They have extremely low boiling points and condense (or freeze) only at very low temperatures, reflecting the weak forces between their atoms. They are also nonflammable and non-toxic (with the important exception of radon’s radioactivity). Under standard conditions you wouldn’t even know these gases are around – they are invisible and imperceptible to our senses. Notably, argon makes up about 0.9% of Earth’s atmosphere by volume (the third most abundant gas in air after nitrogen and oxygen), so these “rare” gases aren’t all that rare. In contrast, neon, helium, krypton, and xenon exist only in trace amounts in air, and radon appears in nature only fleetingly as it decays from radioactive rocks.

One interesting trait of noble gases is that although they are normally inert, they will glow with vivid colors when exposed to an electrical discharge at low pressure. All noble gases are normally invisible, but in gas-discharge tubes like those above, each emits a characteristic glow when excited by electricity. For example, neon shines a brilliant reddish-orange (the classic color of “neon lights”), argon produces a violet-blue glow, and krypton gives off a pale whitish-purple light. These colors arise because each gas’s atoms emit specific wavelengths of light when their electrons are energized.

Despite their reluctance to react, noble gases are far from useless. In fact, they play significant roles in science, technology, and everyday life. Because they are so chemically nonreactive, noble gases are often used to provide inert atmospheres for processes that need protection from oxygen or other reactive gases. For example, welding metals in an argon atmosphere prevents hot metal from oxidizing. The noble gases also shine – literally – in many lighting applications: neon and argon fill glowing advertising signs, krypton is used in certain headlamps and flashlights, and xenon in high-intensity camera flashes and car headlights. Lasers often rely on noble gases as well (for instance, helium-neon lasers, or excimer lasers using argon/krypton compounds). Helium, being extremely light and non-flammable, is well known for lifting balloons and airships, and it also has unique cryogenic uses like cooling the superconducting magnets in MRI scanners. Table 1 at the end of this article provides a quick overview of each noble gas, their symbols and atomic numbers, and a key use or trait.

It’s worth noting that the label “inert” is not 100% true for all noble gases. For a long time chemists assumed these elements could not form compounds at all, but in the 1960s scientists were astonished to discover that heavier noble gases like xenon and krypton can indeed react under extreme conditions. Xenon, for example, can form stable compounds with fluorine (e.g. xenon difluoride), and chemists have even synthesized a few compounds of krypton, argon, and radon. Nonetheless, such reactions require special conditions; under ordinary circumstances the noble gases remain largely aloof and “noble” in their inertness.

Below, we’ll take a tour through each of the noble gases in turn – from the lightest, helium, to the heaviest, oganesson – highlighting their unique characteristics, interesting facts, and how we encounter or use them in science and everyday life.

Helium (He)

Main article: Periodic table/Noble gases/Helium

Helium is the lightest of the noble gases and has an atomic number of 2, making it the second-lightest element in the universe (only hydrogen is lighter). Helium is a colorless, odorless gas that famously has the lowest boiling point of any element – it becomes liquid only at −268.9 °C, just a few degrees above absolute zero. In fact, helium won’t even freeze into a solid at normal atmospheric pressure, no matter how cold it gets. These extreme properties arise from helium’s very small, simple atoms and very weak interatomic forces. Helium was first discovered not on Earth but in the Sun: astronomers in 1868 noticed a mysterious spectral line during a solar eclipse, realizing it came from a new element which they named after Helios (the Greek sun god). It took until 1895 for scientists to isolate helium on Earth, from uranium minerals that emitted helium gas.

Despite being rare in Earth’s atmosphere (only about 0.0005%), helium has become indispensable. Its most well-known use is as a lifting gas for balloons and blimps – helium is much lighter than air and, unlike flammable hydrogen, will not burn. Party balloons, blimps, and high-altitude weather balloons all rely on helium for buoyancy. Helium is also invaluable for its cryogenic (ultra-cold) properties: liquid helium, at just 4 K above absolute zero, is used to cool the powerful magnets in MRI scanners and other superconducting equipment. In scientific research, helium’s low boiling point makes it an ideal coolant for experiments near absolute zero. Helium’s inertness (it doesn’t react or support combustion) also sees it used in deep-sea diving gas mixtures (helium-oxygen mixes help divers avoid “the bends” and nitrogen narcosis) and as a protective atmosphere for welding reactive metals like aluminum. And of course, no mention of helium is complete without the classic squeaky-voice trick – inhaling a bit of helium from a balloon makes sound travel faster through your vocal tract, temporarily raising the pitch of your voice. (It’s a fun party trick, though one should be cautious not to inhale too much and become oxygen-deprived!) In short, helium’s unique lightness and coldness make it a superstar for lifting, cooling, and enabling technologies from airbags to rocket fuel pressurization – not bad for an element that literally disappears into space if we don’t capture it.

Neon (Ne)

Main article: Periodic table/Noble gases/Neon

Neon, atomic number 10, is best known for its brilliant red-orange glow in neon signs. Like helium, neon is a colorless, inert gas under normal conditions. It’s present in Earth’s atmosphere only in minute traces (about 0.0018% by volume), making it rarer on our planet than helium. Neon was discovered in 1898 by British chemists Sir William Ramsay and Morris Travers, who isolated it from liquefied air. They named it “neon” from the Greek neos meaning “new”, since it was a newly found element.

Neon’s claim to fame is without a doubt its use in neon lighting. When an electrical current is passed through neon gas at low pressure, the gas gives off a bright orange-red light. This property was harnessed in the early 20th century to create neon signs, which took the world by storm in the 1920s as a popular form of eye-catching advertising. Classic neon signs (like the “OPEN” sign in a shop window or the neon lights of Las Vegas) owe their reddish glow to neon gas. In fact, “neon lights” has become a generic term for all gas discharge tube signs, though different colors often come from other gases or phosphor coatings – for example, neon yields red-orange, mercury vapor produces blue when combined with phosphor, etc. Pure neon is also used in neon glow lamps (small indicator lights), high-voltage testers, and neon lasers (the common helium-neon laser found in classroom demonstrations). Additionally, liquid neon is sometimes used as a cryogenic refrigerant (it can provide cooling, though helium can reach lower temperatures). While we don’t encounter neon in the air we breathe (it’s too scarce), this noble gas has certainly made its bright mark in lighting up our nights.

Argon (Ar)

Main article: Periodic table/Noble gases/Argon

Argon, atomic number 18, is unique among the noble gases for being abundant right here on Earth. It constitutes just under 1% of Earth’s atmosphere (0.93% by volume), making it the planet’s most common noble gas by far. Every breath you take contains a bit of argon. The name “argon” comes from the Greek argos, meaning “idle” or “inactive,” a nod to argon’s inert nature. This element was discovered in 1894 by Lord Rayleigh and Sir William Ramsay, who were puzzled by an unknown residue in air after removing nitrogen, oxygen, and other known components. The discovery of argon eventually led to the recognition of an entire family of inert gases.

In its characteristics, argon is a colorless, odorless, nonreactive gas very similar to neon and krypton. Because it is inert and readily available (extracted from air), argon has many practical uses. One major use is as a shielding gas in welding. When metals like steel or aluminum are welded, a jet of argon gas is often blown around the weld site to displace oxygen and water vapor, creating a protective bubble so the hot metal doesn’t oxidize or get contaminated. You’ll also find argon filling the space inside ordinary incandescent light bulbs and modern fluorescent tubes. In an incandescent bulb, argon (or sometimes a mix with nitrogen) is used to prevent the hot tungsten filament from burning away too quickly – the argon doesn’t react even at high temperatures, thus prolonging the bulb’s life. In fluorescent lamps, a tiny bit of argon (and mercury vapor) helps the lamp start and also emits ultraviolet light that makes the phosphor coating glow. Argon’s inertness and poor thermal conductivity also make it useful as an insulating filler gas in double-pane windows (helping improve energy efficiency by reducing heat transfer). It has even been used to displace air in packaging of perishable foods (to keep oxygen from spoiling the contents) and in the tires of luxury cars or aircraft. While argon mostly lives up to its “lazy” name – not reacting chemically – it certainly stays busy serving a variety of uses that benefit from a cheap, nonreactive gas.

Krypton (Kr)

Main article: Periodic table/Noble gases/Krypton

Krypton, atomic number 36, often brings to mind Superman’s home planet in popular culture, but in reality this noble gas is very much of Earth – albeit in tiny quantities. Krypton is a rare, colorless gas in our atmosphere (only about 0.0001% of air). Its name comes from the Greek kryptos, meaning “hidden” or “secret,” reflecting the fact that krypton remained hidden in the air until Ramsay and Travers discovered it in 1898 (the same year they found neon and xenon). Krypton gas is inert like its lighter cousins, though under extreme conditions it can form a few compounds (such as krypton difluoride, KrF₂).

In everyday life, krypton is not as widely encountered as neon or argon, but it has some interesting niche applications. Krypton is used in certain types of lighting, especially where a bright white light is needed. For example, krypton gas is used in some flash lamps for high-speed photography. These flash lamps produce intense, short bursts of light (useful for stop-motion photography of fast events), and krypton-filled flashes can have particular advantages in color temperature and duration. Krypton is also sometimes used in “neon” signage or fluorescent bulbs to produce different colors; for instance, krypton can create a pale lavender-white glow in discharge tubes, and mixtures of krypton with other gases are used to generate various hues in lighting. One fascinating fact about krypton is that it once defined a fundamental unit of measure: from 1960 until 1983, the official definition of the meter was based on krypton. Specifically, the meter was defined as 1,650,763.73 wavelengths of a particular orange-red spectral line emitted by krypton-86 gas. Scientists used krypton’s light as a stable reference before the definition switched to the speed of light. Additionally, an isotope of krypton (krypton-85) is released in nuclear reactions, and detecting its presence in the atmosphere can help monitor nuclear activity around the world. Overall, krypton stays mostly behind the scenes – it’s hidden in plain air – but it shines in specialized lighting and even had a hand in the history of our measurement system.

Xenon (Xe)

Main article: Periodic table/Noble gases/Xenon

Xenon, atomic number 54, is one of the heavier noble gases and carries an aura of the exotic. In fact, its very name comes from the Greek xenos, meaning “strange” or “foreign”. Discovered in 1898 by Ramsay and Travers (shortly after they found krypton and neon), xenon is extremely rare in Earth’s atmosphere – about 1 part in 20 million. It’s a colorless, dense gas (about 4.5 times heavier than air) and, like its peers, odorless and chemically inert under most conditions. However, xenon holds a special place in chemistry as the first noble gas found to form true chemical compounds. In 1962, chemist Neil Bartlett famously shocked the scientific world by making xenon react with platinum fluoride to form xenon hexafluoroplatinate. This proved that xenon wasn’t absolutely inert – a groundbreaking discovery that opened the door to many other xenon compounds (such as xenon difluoride, oxides of xenon, and more). Xenon’s willingness to form compounds, albeit with difficulty, is due to its large atomic size and the lesser hold on its outer electrons compared to lighter noble gases.

Beyond its chemical curiosities, xenon has plenty of practical roles. One of the most visible is in lighting. Xenon gas is used in high-power flash lamps and strobe lights – for example, camera flash units and studio strobe lights often contain xenon, which emits an intense white flash when electrified. Xenon short-arc lamps are used in IMAX and cinema projectors to produce extremely bright light, and xenon-filled high-intensity discharge (HID) headlights became popular in luxury cars for their bright, bluish-white illumination. If you’ve ever seen a lighthouse or airport spotlight stabbing the night sky, there’s a good chance xenon arc lamps are at work. Xenon also finds use as a general anesthetic in medicine. Surprisingly, breathing xenon gas can induce anesthesia; it’s not commonly used (due to cost), but it’s valued for being non-toxic and fast-acting, with minimal side effects – an example of an inert gas directly interacting with human biology in a useful way. Another literally out-of-this-world use for xenon is as a propellant for ion engines in spacecraft. NASA’s deep-space probes (like the Dawn spacecraft) have used xenon in their ion thrusters, which ionize the xenon and eject ions to produce a gentle but steady thrust in the vacuum of space. Xenon’s heavy atoms provide more momentum per ion, and its inert nature means it doesn’t damage the engines. Finally, xenon has specialized uses in scientific fields: for instance, xenon isotopes are used in nuclear medicine imaging, and xenon gas is used in NMR (nuclear magnetic resonance) studies as a probing medium. All told, xenon is a noble gas that manages to be both chemically intriguing – for shattering the myth of total inertness – and technologically invaluable, from illuminating our world to propelling spacecraft beyond it.

Radon (Rn)

Main article: Periodic table/Noble gases/Radon

Radon, atomic number 86, stands out from the other noble gases as a radioactive element. It is a heavy, colorless gas – in fact, radon is the densest gas under normal conditions, about 7.5 times heavier than air. Radon is continually generated in nature by the decay of certain radioactive elements like uranium and thorium in rocks and soil. As those elements decay, radon gas is produced and can seep out of the ground. Being inert, radon by itself doesn’t chemically react or cause damage, but the danger comes from its radioactivity. Radon emits ionizing radiation and decays into other radioactive “daughter” elements (like polonium and lead isotopes). If radon gas accumulates in enclosed spaces – for example, in the basements of homes built over uranium-rich soil or granite – its decay products can be inhaled and become lodged in the lungs, delivering a continuous dose of radiation. Long-term exposure to high radon levels is known to increase the risk of lung cancer. In fact, radon is believed to be the second-leading cause of lung cancer (after smoking) and the number one cause among non-smokers. This has made radon a significant environmental health concern. Many homeowners now test for radon and install ventilation systems if levels are high, to disperse the gas.

Radon’s story is a mix of natural science and historical quirk. It was discovered in 1900 by Friedrich Dorn, who called it “radium emanation” since it emanated from radium compounds. Later it was renamed radon. Radon is part of the decay chain of uranium, and because all its isotopes are short-lived (the most stable, radon-222, has a half-life of about 3.8 days), radon in the environment is continuously replenished from radioactive minerals. Physically, radon behaves like a noble gas – it’s inert and monatomic. It condenses to a liquid at about –61.8 °C and freezes around –71 °C, and interestingly, if you cool radon gas, the solid radon glows faintly (yellow to orange-red) due to its intense radioactivity energizing the solid. Historically, radon found some uses in the early 20th century: for example, small sealed glass tubes of radon gas (radon seeds) were used in radiation therapy for cancer, as they emit penetrating gamma rays. There were even “radon spas” where people bathed in radon-rich waters (a practice now recognized as having dubious safety). Today, with our greater understanding of radiation hazards, radon’s main significance is as something to monitor and mitigate in homes. Unlike the other noble gases which we intentionally employ in various technologies, radon is a noble gas we usually want to avoid – except in controlled medical or scientific applications – because of its health risks.

Oganesson (Og)

Main article: Periodic table/Noble gases/Oganesson

Oganesson, atomic number 118, is a special case in the noble gas group. It is the newest and heaviest member of the family, and it is synthetic – meaning it does not occur naturally and has to be created in a laboratory. First synthesized in the early 2000s (with a definitive discovery report in 2006 by a Russian–American team), only a handful of atoms of oganesson have ever been produced. In fact, by 2025, fewer than five atoms had been observed. It was officially named “oganesson” in 2016 to honor Yuri Oganessian, a pioneering nuclear physicist who helped discover numerous superheavy elements. The suffix “-on” in the name aligns with the noble gas naming tradition (as in neon, argon, etc.).

Given that so few atoms of oganesson have existed (and each atom decays in a fraction of a millisecond), its properties remain largely theoretical. Oganesson lies at the bottom of Group 18, but scientists predict it may not behave like a classic noble gas at all. Calculations suggest oganesson’s electrons may be arranged in ways that make it more reactive than the other noble gases, perhaps even somewhat metallic in character. In other words, oganesson might not be “noble” – it could form compounds more readily than radon or xenon, defying the inertness that defines this group. Additionally, because of its extremely large atomic mass and the strong attractive forces between its atoms, oganesson is expected to be solid (or at least liquid) at room temperature, unlike its lighter gaseous cousins. Of course, with no substantial sample of oganesson to test, these properties are predictions for now. As a radioactive element with a half-life measured in milliseconds, oganesson has no practical uses outside of scientific research. Its importance is chiefly in completing the seventh row of the periodic table and helping researchers understand how elements behave at the extremes of atomic size. Oganesson represents the edge of the periodic table as we know it – a frontier element that is teaching chemists and physicists about the limits of atomic structure and periodic trends. Even if we’ll never hold a vial of oganesson gas (or solid oganesson) in our hands, its existence is a triumph of modern science and a reminder that the periodic table, though comprehensive, is still being explored and expanded.

Noble Gases at a Glance (Summary Table)

To summarize the seven noble gases, the table below compares each element’s name, symbol, atomic number, and a key use or notable fact:

Name	Symbol	Atomic Number	Key Use or Notable Property
Helium	He	2	Lifting gas for balloons and airships (non-flammable; extremely low boiling point)
Neon	Ne	10	Neon signs and gas discharge lamps (emits bright red-orange glow in electric light tubes)
Argon	Ar	18	Inert shielding gas for welding; used in light bulbs to protect filaments from oxidation
Krypton	Kr	36	Used in high-speed photography flash lamps and certain fluorescent bulbs (produces whitish-purple glow)
Xenon	Xe	54	Used in high-intensity lamps (e.g. camera flashes, car headlights) and as a general anesthetic gas in medicine
Radon	Rn	86	Radioactive gas that can accumulate in homes (health hazard; leading cause of lung cancer in non-smokers)
Oganesson	Og	118	Highly unstable synthetic element (only a few atoms ever made; decays in milliseconds)

Each of these noble gases contributes in its own way to science and technology – from the commonplace (lighting up signs or filling party balloons) to the cosmic (fueling spacecraft ion engines) to the cautionary (monitoring indoor air for radon). Together, the noble gases demonstrate a fascinating blend of “nothing” – since they barely react – and usefulness, proving that even the most aloof elements have important roles in our world. Whether it’s the glow of neon on a city street, the helium in a child’s balloon, or the argon in a welder’s torch, the noble gases are all around us, quietly making life brighter, safer, and a bit more interesting, all while largely refusing to mix with the chemical crowd.

Sources:

1. Helmenstine, A. M. “Noble Gases Properties, Uses and Sources.” ThoughtCo (2024) – Overview of Group 18 elements, their properties (inertness due to full valence shells, etc.), and common uses.
2. Britannica, “Helium – Chemical Element.” (2025) – Physical properties of helium (lowest boiling point, liquid at –268.9 °C, cannot be frozen at atmospheric pressure); industrial uses of helium in welding, rocketry, balloons, cryogenics, and deep-sea diving mixtures.
3. Britannica, “Neon – Chemical Element.” (2023) – Description of neon’s occurrence and its use in electric signs and discharge lamps (glows reddish-orange when an electric current passes through at low pressure).
4. UCAR Center for Science Education, “Argon.” – Notes that argon is ~0.93% of Earth’s atmosphere and is named from Greek for “inactive”; used as a non-reactive shielding gas in welding and in light bulbs and fluorescent tubes.
5. Compound Interest (Andy Brunning), “IYPT 2019 Elements #36: Krypton.” – Highlights krypton’s use in high-speed photography flashes and the historical definition of the meter by krypton-86’s spectral line.
6. Wikipedia, “Xenon.” (accessed 2025) – Mention of xenon’s applications in flash lamps, arc lamps, anesthesia, and ion propulsion for spacecraft; also the first noble gas compound (xenon hexafluoroplatinate) being synthesized in 1962.
7. Britannica, “Radon – Properties and Effects.” (2025) – Explains radon as a heavy radioactive gas from radium decay, its ability to accumulate in buildings, and its health risks as a cause of lung cancer with prolonged exposure.
8. Helmenstine, A. M. “Oganesson Facts: Element 118.” ThoughtCo (2025) – Overview of oganesson as a synthetic noble gas element with only a few atoms produced, expected to be more reactive than other noble gases and possibly solid or liquid at room temperature.