Argon is an inert, colorless and odorless element — one of the Noble gases. Used in fluorescent lights and in welding, this element gets its name from the Greek word for "lazy," an homage to how little it reacts to form compounds.
On Earth, the vast majority of argon is the isotope argon-40, which arises from the radioactive decay of potassium-40, according to Chemicool. But in space, argon is made in stars, when a two hydrogen nuclei, or alpha-particles, fuse with silicon-32. The result is the isotope argon-36. (Isotopes of an element have varying numbers of neutrons in the nucleus.)
Though inert, argon is far from rare; it makes up 0.94 percent of Earth's atmosphere, according to the Royal Society of Chemistry (RSC). By Chemicool's calculations, that translates to 65 trillion metric tons — and the number increases over time as potassium-40 decays.
Just the facts
According to the Jefferson National Linear Accelerator Laboratory, the properties of argon are:
- Atomic number (number of protons in the nucleus): 18
- Atomic symbol (on the Periodic Table of the Elements): Ar
- Atomic weight (average mass of the atom): 39.948
- Density: 0.0017837 grams per cubic centimeter
- Phase at room temperature: Gas
- Melting point: minus 308.83 degrees Fahrenheit (minus 189.35 degrees Celsius)
- Boiling point: minus 302.53 F (minus 185.85 C)
- Number of isotopes (atoms of the same element with a different number of neutrons): 25; 3 stable
- Most common isotopes: Ar-40 (99.6035 percent natural abundance), Ar-40 (0.0629 percent natural abundance), Ar-36 (0.3336 percent natural abundance)
Uses for an inert gas
The first hint of argon's existence came in 1785, when British scientist Henry Cavendish reported a seemingly inert portion of air, according to the RSC. Cavendish wasn't able to figure out what this mysterious 1 percent was; the discovery would come more than a century later, in 1894. Working concurrently and in communication with Lord Rayleigh (John William Strutt), Scottish chemist William Ramsey identified and described the mysterious gas. The two shared the Nobel Prize in Chemistry in 1904 for the discovery. Argon led to other eureka moments for Ramsey, as well. While investigating the element, he also discovered helium, according to the Nobel Prize organization. Realizing that related elements likely existed, he then found neon, krypton and xenon in quick succession.
Because argon is inert, it is used in industrial processes that require a non-reactive atmosphere. Examples, according to gas supply company Praxair, include welding specialty alloys and producing semiconductor wafers. Argon is also a good insulator, so it's often pumped into deep-sea diving dry suits to keep the diver warm.
Another use for argon is in historical preservation. The gas is pumped around important documents such as a map of the world dating back to 1507 in the Library of Congress, and a copy of the Magna Carta held by the U.S. National Archives. Unlike reactive oxygen, the argon doesn't degrade the paper or ink on delicate documents.
- Neon lights that shine blue actually contain argon, according to Bill Concannon, a neon-sign artist in Crockett, California. (Neon itself makes an orange-red glow.)
- Argon is also used in laser technology, including the argon fluoride (ArF) excimer laser used to do LASIK or PRK surgeries that correct vision. In 1981, IBM's Rangaswamy "Sri" Srinivasan tested out one of these lasers on a leftover Thanksgiving turkey bone and discovered its potential as a surgical tool for delicate operations, according to the Optical Society.
- In September 2014, researchers discovered that contaminated groundwater in Pennsylvania and Texas came not from the oil extraction method known as hydrofracking, but from leaky well casings. They made this discovery by injecting argon and other noble gas tracers into the wells, where they mixed with methane.
- Argon's undergone some changes: In 1957, the International Union of Pure and Applied Chemistry (IUPAC) altered its atomic symbol from "A" to today's "Ar."
For many years, the noble gas xenon has been researched as a treatment for brain injuries. Xenon, however, is expensive, leading researchers to turn to its noble gas cousin, argon, as a potential alternative.
The research field is still young, but experiments in cell cultures and in animals suggest that argon could one day be used to limit brain damage after traumatic injuries or oxygen deprivation. One review published in the journal Medical Gas Research in February 2014 found that in most cases, argon treatment reduces brain cell death by significant amounts — 15 to 25 percent, said Derek Nowrangi, one of the paper's authors and a doctoral student at the Loma Linda University School of Medicine in California.
No one yet understands why argon has this effect. Brain cells communicate with the use of chemicals called neurotransmitters and with neuroreceptors that fit together like lock and key. Most likely, Nowrangi told Live Science, the gas acts on these neuroreceptors, specifically the NMDA receptor (which stands for N-methyl-D-aspartate for the neurotransmitter it receives) or the GABA receptor (which stands for gamma-aminobutyric acid). Somehow, when taken up by these receptors, the argon seems to act to prevent cells from self-destructing in response to brain damage.
In research, argon gas is either directly applied to cells in a culture dish that are under stress, such as an oxygen- and glucose-deprived environment, or given mixed with oxygen in a facemask for animal studies. Researchers then quantify the number of cells that died with and without argon treatment.
As research on argon picks up, it's more likely that human trials will begin, Nowrangi said. But there are caveats: Some studies find mixed results or negative effects to argon treatment. In one, Nowrangi said, the brain as a whole seemed protected by argon, but damage to one area was actually increased with the gas treatment. This could be because the argon didn't penetrate to that region, or because different brain regions have different cell types and cell densities.
"This still needs a lot of research to be actually able to translate into the clinic," Nowrangi said.
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Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.