The noble gases are the elements in group 18 on the periodic table. Atoms of these elements have filled valence electron shells, making them relatively inert, colorless, odorless, monatomic gases at room temperature and pressure.
Why Are Noble Gases Called Noble?
The term “noble gas” comes from a translation of the German word Edelgas, which means noble gas. German chemist Hugo Erdmann coined the phrase in 1898. Like a nobleman might consider it undignified to associate with commoners, noble gases tend not to react with other elements.
Other names for noble gases include rare gases, inert gases, and aerogens. When referencing the periodic table, the noble gases are IUPAC group 18 (group 0 under the old method), CAS group VIIIA, the helium group, or the neon group.
List of Noble Gases
There are either six or seven noble gas elements, depending on whether or not you include element 118, oganesson.
The first six elements occur naturally. Radon and oganesson are radioactive elements. Oganesson is a man-made (synthetic) element that doesn’t entirely fit into the group. While it may have a filled valence shell (7p6), it is predicted to be a metallic solid at room temperature.
Noble Gas Properties
Elements in the noble gas group share common chemical and physical properties:
- Behave as nearly ideal gases under standard conditions
- Monatomic gases at room temperature
- Fairly nonreactive
- Complete outer electron or valence shell (oxidation number = 0)
- High ionization energies
- Very low electronegativity values
- Low melting points
- Low boiling points
- No color, odor, or flavor under ordinary conditions (but may form colored liquids and solids)
- Conduct electricity and fluoresce at low pressure
The most common misconception about the noble gases is that they cannot form chemical bonds and compounds. While their atoms normally have filled valence shells, it’s possible to remove one or more electrons or (less commonly) add electrons. Under certain conditions, the noble gases can form diatomic gases, clathrates, fluorides, chlorides, metal complexes, and other compounds. Usually, compounds form under extremely high pressures. Examples of noble gas compounds include argon fluorohydride (HArF) and xenon hexafluoride (XeF6).
Another misconception is that the noble gases are rare. As with the rare earths, the rare gases aren’t particularly uncommon. Argon is the third or fourth most abundant gas in the atmosphere (depending on the amount of water vapor). It accounts for 1.3% of the atmospheric mass or 0.94% of its volume. Neon, krypton, helium, and xenon are trace elements in air. The gases may be more abundant deeper within the earth. Helium is found in natural gas, while xenon occurs in vapors from some mineral springs and may bind with iron and nickel in the Earth’s core.
Noble Gas Uses
The noble gases have several important uses. They are used as an inert atmosphere to protect specimens and minimize chemical reactions. Their low melting and boiling points make them useful as refrigerants. The noble gases are important in lighting applications, such as high-intensity lamps, neon lights, car headlamps, and excimer lasers. Helium is used in balloons, in breathing gas mixtures for deep-sea diving, and to cool superconducting magnets. The gases, especially xenon, are used in ion drives. At present, oganesson has no practical uses, but it might help scientists make even heavier elements someday.
Noble Gas Sources
Neon, argon, krypton, and xenon come from fractional distillation of liquefied air. The primary source of helium is cryogenic separation of natural gas. Radon comes from radioactive decay of radium, thorium, uranium, and other heavy radioactive elements. Oganesson is a man-made element synthesized by striking a target with accelerated particles. In the future, noble gases may be sourced from other planets. For example, helium and xenon are much more abundant on Jupiter and other gas planets than on Earth.
- Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements (2nd ed.). Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.
- Lehmann, J (2002). “The Chemistry of Krypton”. Coordination Chemistry Reviews. 233–234: 1–39. doi:10.1016/S0010-8545(02)00202-3
- Ozima, Minoru; Podosek, Frank A. (2002). Noble Gas Geochemistry. Cambridge University Press. ISBN 0-521-80366-7.
- Partington, J. R. (1957). “Discovery of Radon”. Nature. 179 (4566): 912. doi:10.1038/179912a0
- Renouf, Edward (1901). “Noble gases”. Science. 13 (320): 268–270.