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noble gas

 
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n.

Any of the elements in Group O of the periodic table, including helium, neon, argon, krypton, xenon, and radon, which are monatomic and with limited exceptions chemically inert. Also called inert gas.


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Science of Everyday Things: Noble Gases
 
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Concept

Along the extreme right-hand column of the periodic table of elements is a group known as the noble gases: helium, neon, argon, krypton, xenon, and radon. Also known as the rare gases, they once were called inert gases, because scientists believed them incapable of reacting with other elements. Rare though they are, these gases are a part of everyday life, as evidenced by the helium in balloons, the neon in signs—and the harmful radon in some American homes.

How It Works

Defining the Noble Gases

The periodic table of elements is ordered by the number of protons in the nucleus of an atom for a given element (the atomic number), yet the chart is also arranged in such a way that elements with similar characteristics are grouped together. Such is the case with Group 8, which is sometimes called Group 18, a collection of non-metals known as the noble gases. The six noble gases are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Their atomic numbers are, respectively, 2, 10, 18, 36, 54, and 86.

Several characteristics, aside from their placement on the periodic table, define the noble gases. Obviously, all are gases, meaning that they only form liquids or solids at extremely low temperatures—temperatures that, on Earth at least, are usually only achieved in a laboratory. They are colorless, odorless, and tasteless, as well as monatomic—meaning that they exist as individual atoms, rather than in molecules. (By contrast, atoms of oxygen—another gas, though not among this group—usually combine to form a molecule, O2.)

Low Reactivity

There is a reason why noble gas atoms tend not to combine: one of the defining characteristics of the noble gas "family" is their lack of chemical reactivity. Rather than reacting to, or bonding with, other elements, the noble gases tend to remain apart—hence the name "noble," implying someone or something that is set apart from the crowd, as it were. Due to their apparent lack of reactivity, the noble gases—also known as the rare gases—were once known as the inert gases.

Indeed, helium, neon, and argon have not been found to combine with other elements to form compounds. However, in 1962 English chemist Neil Bartlett (1932-) succeeded in preparing a compound of xenon with platinum and fluorine (XePtF6), thus overturning the idea that the noble gases were entirely "inert." Since that time, numerous compounds of xenon with other elements, most notably oxygen and fluorine, have been developed. Fluorine has also been used to form simple compounds with krypton and radon.

Nonetheless, low reactivity—instead of no reactivity, as had formerly been thought—characterizes the rare gases. One of the factors governing the reactivity of an element is its electron configuration, and the electrons of the noble gases are arranged in such a way as to discourage bonding with other elements.

Real-Life Applications

Isolation of the Noble Gases

Helium

Helium is an unusual element in many respects—not least because it is the only element to have first been identified in the Solar System before it was discovered on Earth. This is significant, because the elements on Earth are the same as those found in space: thus, it is more than just an attempt at sounding poetic when scientists say that humans, as well as the world around them, are made from "the stuff of stars."

In 1868, a French astronomer named Pierre Janssen (1824-1907) was in India to observe a total solar eclipse. To aid him in his observations, he used a spectroscope, an instrument for analyzing the spectrum of light emitted by an object. What Janssen's spectroscope showed was surprising: a yellow line in the spectrum, never seen before, which seemed to indicate the presence of a previously undiscovered element. Janssen called it "helium" after the Greek god Helios, or Apollo, whom the ancients associated with the Sun.

Janssen shared his findings with English astronomer Sir Joseph Lockyer (1836-1920), who had a worldwide reputation for his work in analyzing light waves. Lockyer, too, believed that what Janssen had seen was a new element, and a few months later, he observed the same unusual spectral lines. At that time, the spectroscope was still a new invention, and many members of the worldwide scientific community doubted its usefulness, and therefore, in spite of Lockyer's reputation, they questioned the existence of this "new" element. Yet during their lifetimes, Janssen and Lockyer were proven correct.

Neon, Argon, Krypton, and Xenon

They had to wait a quarter century, however. In 1893, English chemist Sir William Ramsay (1852-1916) became intrigued by the presence of a mysterious gas bubble left over when nitrogen from the atmosphere was combined with oxygen. This was a phenomenon that had also been noted by English physicist Henry Cavendish (1731-1810) more than a century before, but Cavendish could offer no explanation. Ramsay, on the other hand, had the benefit of observations made by English physicist John William Strutt, Lord Rayleigh (1842-1919).

Up to that time, scientists believed that air consisted only of oxygen, carbon dioxide, and water vapor. However, Rayleigh had noticed that when nitrogen was extracted from air after a process of removing those other components, it had a slightly higher density than nitrogen prepared from a chemical reaction. In light of his own observations, Ramsay concluded that whereas nitrogen obtained from chemical reactions was pure, the nitrogen extracted from air contained trace amounts of an unknown gas.

Ramsay was wrong in only one respect: hidden with the nitrogen was not one gas, but five. In order to isolate these gases, Ramsay and Rayleigh subjected air to a combination of high pressure and low temperature, allowing the various gases to boil off at different temperatures. One of the gases was helium—the first confirmation that the element existed on Earth—but the other four gases were previously unknown. The Greek roots of the names given to the four gases reflected scientists' wonder at discovering these hard-to-find elements: neos (new), argos (in active), kryptos (hidden), and xenon (stranger).

Radon

Inspired by the studies of Polish-French physicist and chemist Marie Curie (1867-1934) regarding the element radium and the phenomenon of radioactivity (she discovered the element, and coined the latter term), German physicist Friedrich Dorn (1848-1916) became fascinated with radium. Studying the element, he discovered that it emitted a radioactive gas, which he dubbed "radium emanation." Eventually, however, he realized that what was being produced was a new element. This was the first clear proof that one element could become another through the process of radioactive decay.

Ramsay, who along with Rayleigh had received the Nobel Prize in 1904 for his work on the noble gases, was able to map the new element's spectral lines and determine its density and atomic mass. A few years later, in 1918, another scientist named C. Schmidt gave it the name "radon." Due to its behavior and the configuration of its electrons, chemists classified radon among what they continued to call the "inert gases" for another half-century—until Bartlett's preparation of xenon compounds in 1962.

Presence of the Rare Gases on Earth

In the Atmosphere

Though the rare gases are found in minerals and meteorites on Earth, their greatest presence is in the planet's atmosphere. It is believed that they were released into the air long ago as a by-product of decay on the part of radioactive materials in the Earth's crust. Within the atmosphere, argon is the most "abundant"—in comparative terms, given the fact that the "rare gases" are, by definition, rare.

Nitrogen makes up about 78% of Earth's atmosphere and oxygen 21%, meaning that these two elements constitute fully 99% of the air above the Earth. Argon ranks a distant third, with 0.93%. The remaining 0.07% is made up on water vapor, carbon dioxide, ozone (O3), and traces of the noble gases. These are present in such small quantities that the figures for them are not typically presented as percentages, but rather in terms of parts per million (ppm). The concentrations of neon, helium, krypton, and xenon in the atmosphere are 18, 5, 1, and 0.09 ppm respectively.

In the Soil

Radon in the atmosphere is virtually negligible, which is a fortunate thing, in light of its radioactive qualities. Few Americans, in fact, even knew of its existence until 1988, when the United States Environmental Protection Agency (EPA) released a report estimating that some ten million American homes had potentially harmful radon levels. This set off a scare, and during the late 1980s and 1990s, sales of home radon detectors boomed. Meanwhile, the federal government increased concerns with additional reports, advising people to seal their basements and ventilate their homes if radon exceeded certain levels.

A number of scientists have disputed the government's claims, yet some regions of the United States appear to be at relatively high risk due to the presence of radon in the soil. The element seems to be most plentiful in soils containing high concentrations of uranium. If radon is present in a home that has been weather-sealed to improve the efficiency of heating and cooling systems, it is indeed potentially dangerous to the residents.

Chinese scientists in the 1960s made an interesting discovery regarding radon and its application to seismography, or the area of the earth sciences devoted to studying and predicting earthquakes. Radon levels in groundwater, the Chinese reports showed, rise considerably just before an earthquake. Since then, the Chinese have monitored radon concentrations in water, and used this data to predict earthquakes.

Extracting Rare Gases

Radon, in fact, is not the only rare gas that can be obtained as the result of radioactive decay: in 1903, Ramsay and British chemist Frederick Soddy (1877-1956) showed that the breakdown of either uranium or radium results in the production of helium atoms (beta particles). A few years later, English physicist Ernest Rutherford (1871-1937) demonstrated that radiation carrying a positive electrical charge (alpha rays) was actually a stream of helium atoms stripped of an electron.

Many of the noble gases are extracted by liquefying air—that is, by reducing it to temperatures at which it assumes the properties of a liquid rather than a gas. By controlling temperatures in the liquefied air, it is possible to reach the boiling point for a particular noble gas and thereby extract it, much as was done when these gases were first isolated in the 1890s.

The Unique Situation of Helium

Helium is remarkable, in that it only liquefies at a temperature of −457.6°F (−272°C), just above absolute zero. Absolute zero is the temperature at which the motion of atoms or molecules comes to a virtual stop, but the motion of helium atoms never completely ceases. In order to liquefy it, in fact, even at those low temperatures, it must be subjected to pressures many times that exerted by Earth's atmosphere.

Given these facts, it is difficult to extract helium from air. More often, it is obtained from natural gas wells, where it is present in relatively large concentrations—between 1% and 7% of the natural gas. The majority of the Earth's helium supply belongs to the United States, where the greatest abundance of helium-supplying wells are in Texas, Oklahoma, and Kansas. During World War II, the United States took advantage of this supply of relatively inexpensive helium to provide buoyancy for a fleet of airships used for reconnaissance.

There is one place with an abundant supply of helium, but there are no plans for a mining expedition any time soon. That place is the Sun, where the nuclear fusion of hydrogen atoms creates helium. Indeed, helium seems to be the most plentiful element of all, after hydrogen, constituting 23% of the total mass of the universe. Why, then, is it so difficult to obtain on Earth? Most likely because it is so light in comparison to air; it simply floats off into space.

Applications for the Noble Gases

Radon, Argon, Krypton, and Xenon

Though radon is known primarily for the hazards it poses to human life and well-being, it has useful applications. As noted above, its presence in groundwater appears to provide a possible means of predicting earthquakes. In addition, it is used for detecting leaks, measuring flow rates, and inspecting metal welds.

One interesting use of argon and, in particular, the stable isotope argon-40, is in dating techniques used by geologists, paleontologists, and other scientists studying the distant past. When volcanic rocks are subjected to extremely high temperatures, they release argon, and as the rocks cool, argon-40 accumulates. Because argon-40 is formed by the radioactive decay of a potassium isotope, potassium-40, the amount of argon-40 that forms is proportional to the rate of decay for potassium-40. The latter has a half-life of 1.3 billion years, meaning that it takes 1.3 billion years for half the potassium-40 originally present to be converted to argon-40. Using argon-40, paleontologists have been able to estimate the age of volcanic layers above and below fossil and artifact remains in east Africa.

Krypton has a number of specialized applications—for instance, it is mixed with argon and used in the manufacture of windows with a high level of thermal efficiency. Used in lasers, it is often mixed with a halogen such as fluorine. In addition, it is also sometimes used in halogen sealed-beam headlights. Many fans of Superman, no doubt, were disappointed at some point in their lives to discover that there is no such thing as "kryptonite," the fictional element that caused the Man of Steel to lose his legendary strength. Yet krypton—the real thing—has applications that are literally out of this world. In the development of fuel for space exploration, krypton is in competition with its sister element, xenon. Xenon offers better performance, but costs about ten times more to produce; thus krypton has become more attractive as a fuel for space flight.

In addition to its potential as a space fuel, xenon is used in arc lamps for motion-picture film projection, in high-pressure ultraviolet radiation lamps, and in specialized flashbulbs used by photographers. One particular isotope of xenon is utilized for tracing the movement of sands along a coastline. Xenon is also applied in high-energy physics for detecting nuclear radiation in bubble chambers. Furthermore, neuroscientists are experimenting with the use of xenon in diagnostic procedures to clarify x-ray images of the human brain.

Neon

Neon, of course, is best-known for its application in neon signs, which produce an eye-catching glow when lit up at night. French chemist Georges Claude (1870-1960), intrigued by Ramsay's discovery of neon, conducted experiments that led to the development of the neon light in 1910. That first neon light was simply a glass tube filled with neon gas, which glowed a bright red when charged with electricity.

Claude eventually discovered that mixing other gases with neon produced different colors of light. He also experimented with variations in the shapes of glass tubes to create letters and pictures. By the 1920s, neon light had come into vogue, and it is still popular today. Modern neon lamps are typically made of plastic rather than glass, and the range of colors is much greater than in Claude's day: not only the gas filling, but the coating inside the tube, is varied, resulting in a variety of colors from across the spectrum.

Though the neon sign is its best-known application, neon is used for many other things. Neon glow lamps are often used to indicate on/off settings on electronic instrument panels, and lightweight neon lamps are found on machines ranging from computers to voltage regulators. In fact, the first practical color television, produced in 1928, used a neon tube to produce the red color in the receiver. Green came from mercury, but the blue light in that early color TV came from another noble gas, helium.

Helium

Helium, of course, is widely known for its use in balloons—both for large airships and for the balloons that have provided joy and fun to many a small child. Though helium is much more expensive than hydrogen as a means of providing buoyancy to airships, hydrogen is extremely flammable, and after the infamous explosion of the airship Hindenburg in 1937, helium became the preferred medium for airships. As noted earlier, the United States military made extensive use of helium-filled airships during the World War II.

The use of helium for buoyancy is one of the most prominent applications of this noble gas, but far from the only one. In fact, not only have people used helium to go up in balloons, but divers use helium for going down beneath the surface of the ocean. In that situation, of course, helium is not used for providing buoyancy, but as a means of protecting against the diving-related condition known as "the bends," which occurs when nitrogen in the blood bubbles as the diver rises to the surface. Helium is mixed with oxygen in diver's air tanks because it does not dissolve in the blood as easily as nitrogen.

Among the most fascinating applications of helium relate to its extraordinarily low freezing point. Helium has played a significant role in the low-temperature science known as cryogenics, and has found application in research concerning superconductivity: the use of very low temperatures to develop materials that conduct electrical power with vastly greater efficiency than ordinary conductors. Close to absolute zero, helium transforms into a highly unusual liquid unlike any known substance, in that it has no measurable resistance to flow. This means that it could carry an electrical current hundreds of times more efficiently than a copper wire.

Where to Learn More

"The Chemistry of the Rare Gases" (Web site). <http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch10/raregas.html> (May 13, 2001).

"Homework: Science: Chemistry: Gases" Channelone.com (Web site). <http://www.channelone.com/fasttrack/science/chemistry/gases.html> (May 12, 2001).

Knapp, Brian J.; David Woodroffe; David A. Hardy. Elements. Danbury, CT: Grolier Educational, 2000.

Mebane, Robert C. and Thomas R. Rybolt. Air and OtherGases. Illustrations by Anni Matsick. New York: Twenty-First Century Books, 1995.

"Noble Gases" Xrefer.com (Web site). <http://www.xrefer.com/entry/643259> (May 13, 2001).

Rare Gases. Praxair (Web site). <http://www.praxair.com/Praxair.nsf/X1/gase_rarega?openDocument> (May 13, 2001).

Stwertka, Albert. Superconductors: The Irresistible Future. New York: F. Watts, 1991.

Taylor, Ron. Facts on Radon and Asbestos. Illustrated by Ian Moores. New York: F. Watts, 1990.

 
Dental Dictionary: noble gas
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n

A gas that will not oxidize; the inert gases (for example, helium and neon).

 
Britannica Concise Encyclopedia: noble gas
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Any of the seven chemical elements that make up the rightmost group of the periodic table as usually arranged: helium, neon, argon, krypton, xenon, radon, and element 118. All are colourless, odourless, and nonflammable and, except for element 118, occur in tiny amounts in the atmosphere (though helium is the most plentiful element in the universe after hydrogen). Their stable electronic configurations, with no unpaired electrons to share, make them extremely unreactive — hence "noble" (i.e., aloof) or inert — though krypton, xenon, and radon, with outer electrons held less firmly, can form compounds (mainly with fluorine). These gases absorb and give off electromagnetic radiation in a much less complex way than other substances, a property exploited in their use in fluorescent lighting devices and discharge lamps. They glow with a characteristic colour when confined in a transparent container at low pressure with an electric current passing through it. Their very low boiling and melting points make them useful as refrigerants for low-temperature research (see cryogenics).

For more information on noble gas, visit Britannica.com.

 
Wikipedia: Noble gas
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Group → 18
↓ Period
1 2
He
2 10
Ne
3 18
Ar
4 36
Kr
5 54
Xe
6 86
Rn
7 118
Uuo
Legend
Noble gas
Gas
Primordial element
From decay
Synthetic

The noble gases are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with a very low chemical reactivity. The six noble gases that occur naturally are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn).

For the first six periods of the periodic table, the noble gases are exactly the members of group 18 (8A) of the periodic table (previously known as group 0). However, this no longer hold in the seventh period (due to relativistic effects): The next member of group 18, ununoctium, is probably not a noble gas.[1] Instead, group 14 member ununquadium exhibits noble-gas-like properties.[2]

The properties of the noble gases can be well explained by modern theories of atomic structure: their outer shell of valence electrons is considered to be "full", giving them little tendency to participate in chemical reactions, and only a few hundred noble gas compounds have been prepared. The melting and boiling points for each noble gas are close together, differing by less than 10 °C (18 °F); consequently, they are liquids only over a small temperature range.

Neon, argon, krypton, and xenon are obtained from air using the methods of liquefaction of gases and fractional distillation. Helium is typically separated from natural gas, and radon is usually isolated from the radioactive decay of dissolved radium compounds. Noble gases have several important applications in industries such as lighting, welding, and space exploration. A helium-oxygen breathing gas is often used by deep-sea divers at depths of seawater over 180 feet (55 m) to keep the diver from experiencing oxygen toxemia, the lethal effect of high-pressure oxygen, and nitrogen narcosis, the distracting narcotic effect of the nitrogen in air beyond this partial-pressure threshold. After the risks caused by the flammability of hydrogen became apparent, it was replaced with helium in blimps and balloons.

Contents

History

Noble gas is translated from the German noun Edelgas, first used in 1898 by Hugo Erdmann[3] to indicate their extremely low level of reactivity. The name makes an analogy to the term "noble metals", such as gold, which were associated with wealth and nobility, and also have low reactivity. The noble gases have also been referred to as inert gases, but this label is now deprecated as many noble gas compounds are now known.[4] Rare gases is another term that was used,[5] but this is also inaccurate because argon forms a fairly considerable part (0.94% by volume, 1.3% by mass) of the Earth's atmosphere.[6]

Helium was first detected in the Sun due to its characteristic spectral lines.

Pierre Janssen and Joseph Norman Lockyer were the first to discover a noble gas on August 18, 1868 while looking at the chromosphere of the Sun, and named it helium after the Greek word for the Sun, ήλιος (ílios or helios).[7] Before them, in 1784, the English chemist and physicist Henry Cavendish had discovered that air contains a small proportion of a substance less reactive than nitrogen.[8] A century later, in 1895, Lord Rayleigh discovered that samples of nitrogen from the air were of a different density than nitrogen resulting from chemical reactions. Along with scientist William Ramsay at University College, London, Lord Rayleigh theorized that the nitrogen extracted from air was mixed with another gas, leading to an experiment that successfully isolated a new element, argon, from the Greek word αργός (argós, "inactive").[8] With this discovery, they realized an entire class of gases was missing from the periodic table. During his search for argon, Ramsay also managed to isolate helium for the first time while heating cleveite, a mineral. In 1902, having accepted the evidence for the elements helium and argon, Dmitri Mendeleev included these noble gases as group 0 in his arrangement of the elements, which would later become the periodic table.[9]

Ramsay continued to search for these gases using the method of fractional distillation to separate liquid air into several components. In 1898, he discovered the elements krypton, neon, and xenon, and named them after the Greek words κρυπτός (kryptós, "hidden"), νέος (néos, "new"), and ξένος (xénos, "stranger"), respectively. Radon was first identified in 1898 by Friedrich Ernst Dorn,[10] and was named radium emanation, but was not considered a noble gas until 1904 when its characteristics were found to be similar to those of other noble gases.[11] Rayleigh and Ramsay received the 1904 Nobel Prizes in Physics and in Chemistry, respectively, for their discovery of the noble gases;[12][13] in the words of J. E. Cederblom, then president of the Royal Swedish Academy of Sciences, "the discovery of an entirely new group of elements, of which no single representative had been known with any certainty, is something utterly unique in the history of chemistry, being intrinsically an advance in science of peculiar significance".[13]

The discovery of the noble gases aided in the development of a general understanding of atomic structure. In 1895, French chemist Henri Moissan attempted to form a reaction between fluorine, the most electronegative element, and argon, one of the noble gases, but failed. Scientists were unable to prepare compounds of argon until the end of the 20th century, but these attempts helped to develop new theories of atomic structure. Learning from these experiments, Danish physicist Niels Bohr proposed in 1913 that the electrons in atoms are arranged in shells surrounding the nucleus, and that for all noble gases except helium the outermost shell always contains eight electrons.[11] In 1916, Gilbert N. Lewis formulated the octet rule, which concluded an octet of electrons in the outer shell was the most stable arrangement for any atom; this arrangement caused them to be unreactive with other elements since they did not require any more electrons to complete their outer shell.[14]

It was not until 1962 that Neil Bartlett discovered the first chemical compound of a noble gas, xenon hexafluoroplatinate.[15] Compounds of other noble gases were discovered soon after: in 1962 for radon, radon fluoride,[16] and in 1963 for krypton, krypton difluoride (KrF2).[17] The first stable compound of argon was reported in 2000 when argon fluorohydride (HArF) was formed at a temperature of 40 K (−233.2 °C; −387.7 °F).[18]

In December 1998, scientists at the Joint Institute for Nuclear Research working in Dubna, Russia bombarded plutonium (Pu) with calcium (Ca) to produce a single atom of element 114,[19] which they temporarily named ununquadium (Uuq).[20] Preliminary chemistry experiments have indicated this element may be the first superheavy element to show abnormal noble-gas-like properties, even though it is a member of group 14 on the periodic table.[21] In October 2006, scientists from the Joint Institute for Nuclear Research and Lawrence Livermore National Laboratory successfully created synthetically ununoctium (Uuo), the seventh element in group 18,[22] by bombarding californium (Cf) with calcium (Ca).[23]

Physical and atomic properties

Property[11][24] Helium Neon Argon Krypton Xenon Radon
Density (g/dm³) 0.1786 0.9002 1.7818 3.708 5.851 9.97
Boiling point (K) 4.4 27.3 87.4 121.5 166.6 211.5
Melting point (K) 0.95[25] 24.7 83.6 115.8 161.7 202.2
Enthalpy of vaporization (kJ/mol) 0.08 1.74 6.52 9.05 12.65 18.1
Solubility in water at 20 °C (cm3/kg) 8.61 10.5 33.6 59.4 108.1 230
Atomic number 2 10 18 36 54 86
Atomic radius (calculated) (pm) 31 38 71 88 108 120
Ionization energy (kJ/mol) 2372 2080 1520 1351 1170 1037
Allen electronegativity[citation needed] 4.16 4.79 3.24 2.97 2.58 2.60
For more data, see Noble gas (data page).

The noble gases have weak interatomic force, and consequently have very low melting and boiling points. They are all monatomic gases under standard conditions, including the elements with larger atomic masses than many normally solid elements.[11] Helium has several unique qualities when compared with other elements: its boiling and melting points are lower than those of any other known substance; it is the only element known to exhibit superfluidity; it is the only element that cannot be solidified by cooling under standard conditions—a pressure of 25 standard atmospheres (2,500 kPa; 370 psi) must be applied at a temperature of 0.95 K (−272.200 °C; −457.960 °F) to convert it to a solid.[26] The noble gases up to xenon have multiple stable isotopes. Radon has no stable isotopes; its longest-lived isotope, 222Rn, has a half-life of 3.8 days and decays to form helium and polonium, which ultimately decays to lead.[11]

This is a plot of ionization potential versus atomic number. The noble gases, which are labeled, have the largest ionization potential for each period.

The noble gas atoms, like atoms in most groups, increase steadily in atomic radius from one period to the next due to the increasing number of electrons. The size of the atom is related to several properties. For example, the ionization potential decreases with an increasing radius because the valence electrons in the larger noble gases are farther away from the nucleus and are therefore not held as tightly together by the atom. Noble gases have the largest ionization potential among the elements of each period, which reflects the stability of their electron configuration and is related to their relative lack of chemical reactivity.[24] Some of the heavier noble gases, however, have ionization potentials small enough to be comparable to those of other elements and molecules. It was the insight that xenon has an ionization potential similar to that of the oxygen molecule that led Bartlett to attempt oxidizing xenon using platinum hexafluoride, an oxidizing agent known to be strong enough to react with oxygen.[15] Noble gases cannot accept an electron to form stable anions; that is, they have a negative electron affinity.[27]

The macroscopic physical properties of the noble gases are dominated by the weak van der Waals forces between the atoms. The attractive force increases with the size of the atom as a result of the increase in polarizability and the decrease in ionization potential. This results in systematic group trends: as one goes down group 18, the atomic radius, and with it the interatomic forces, increases, resulting in an increasing melting point, boiling point, enthalpy of vaporization, and solubility. The increase in density is due to the increase in atomic mass.[24]

The noble gases are nearly ideal gases under standard conditions, but their deviations from the ideal gas law provided important clues for the study of intermolecular interactions. The Lennard-Jones potential, often used to model intermolecular interactions, was deduced in 1924 by John Lennard-Jones from experimental data on argon before the development of quantum mechanics provided the tools for understanding intermolecular forces from first principles.[28] The theoretical analysis of these interactions became tractable because the noble gases are monatomic and the atoms spherical, which means that the interaction between the atoms is independent of direction, or isotropic.

Chemical properties

Neon, like all noble gases, has a full valence shell. Noble gases have eight electrons in the outermost shell, except in the case of helium, which has two.

The noble gases are colorless, odorless, tasteless, and nonflammable under standard conditions. They were once labeled group 0 in the periodic table because it was believed they had a valence of zero, meaning their atoms cannot combine with those of other elements to form compounds. However, it was later discovered some do indeed form compounds, causing this label to fall into disuse.[11] Very little is known about the properties of the most recent member of group 18, ununoctium (Uuo).[29]

Like other groups, the members of this family show patterns in its electron configuration, especially the outermost shells resulting in trends in chemical behavior:

Z Element No. of electrons/shell
2 helium 2
10 neon 2, 8
18 argon 2, 8, 8
36 krypton 2, 8, 18, 8
54 xenon 2, 8, 18, 18, 8
86 radon 2, 8, 18, 32, 18, 8
118 ununoctium 2, 8, 18, 32, 32, 18, 8

The noble gases have full valence electron shells. Valence electrons are the outermost electrons of an atom and are normally the only electrons that participate in chemical bonding. Atoms with full valence electron shells are extremely stable and therefore do not tend to form chemical bonds and have little tendency to gain or lose electrons.[30] However, heavier noble gases such as radon are held less firmly together by electromagnetic force than lighter noble gases such as helium, making it easier to remove outer electrons from heavy noble gases.

As a result of a full shell, the noble gases can be used in conjunction with the electron configuration notation to form the noble gas notation. To do this, the nearest noble gas that precedes the element in question is written first, and then the electron configuration is continued from that point forward. For example, the electron notation of carbon is 1s²2s²2p², and the noble gas notation is [He]2s²2p². This notation makes it easier to identify elements, and is shorter than writing out the full notation of atomic orbitals.[31]

Compounds

Main article: Noble gas compound
Structure of XeF4, one of the first noble gas compounds to be discovered

The noble gases show extremely low chemical reactivity; consequently, only a few hundred noble gas compounds have been formed. Neutral compounds in which helium and neon are involved in chemical bonds have not been formed (although there are some theoretical evidence for a few helium compounds), while xenon, krypton, and argon have shown only minor reactivity.[32] The reactivity follows the order Ne < He < Ar < Kr < Xe < Rn.

In 1933, Linus Pauling predicted that the heavier noble gases could form compounds with fluorine and oxygen. He predicted the existence of krypton hexafluoride (KrF6) and xenon hexafluoride (XeF6), speculated XeF8 might exist as an unstable compound, and suggested xenic acid could form perxenate salts.[33][34] These predictions were shown to be generally accurate, except XeF8 is now thought to be both thermodynamically and kinetically unstable.[35]

Xenon compounds are the most numerous of the noble gas compounds that have been formed.[36] Most of them have the xenon atom in the oxidation state of +2, +4, +6, or +8 bonded to highly electronegative atoms such as fluorine or oxygen, as in xenon difluoride (XeF2), xenon tetrafluoride (XeF4), xenon hexafluoride (XeF6), xenon tetroxide (XeO4), and sodium perxenate (Na4XeO6). Some of these compounds have found use in chemical synthesis as oxidizing agents; XeF2, in particular, is commercially available and can be used as a fluorinating agent.[37] As of 2007, about five hundred compounds of xenon bonded to other elements have been identified, including organoxenon compounds (those bonded to carbon), and xenon bonded to nitrogen, chlorine, gold, mercury, and xenon itself.[32][38] Compounds of xenon bound to boron, hydrogen, bromine, iodine, beryllium, sulphur, titanium, copper, and silver have also been observed but only at low temperatures in noble gas matrices, or in supersonic noble gas jets.[32]

In theory, radon is more reactive than xenon, and therefore should form chemical bonds more easily than xenon does. However, due to the high radioactivity and short half-life of radon isotopes, only a few fluorides and oxides of radon have been formed in practice.[39]

Krypton is less reactive than xenon, but several compounds have been reported with krypton in the oxidation state of +2.[32] Krypton difluoride is the most notable and easily characterized. Compounds in which krypton forms a single bond to nitrogen and oxygen have also been characterized,[40] but are only stable below −60 °C (−76.0 °F) and −90 °C (−130.0 °F) respectively).[32]

Krypton atoms chemically bound to other nonmetals (hydrogen, chlorine, carbon) as well as some late transition metals (copper, silver, gold) have also been observed, but only either at low temperatures in noble gas matrices, or in supersonic noble gas jets.[32] Similar conditions were used to obtain the first few compounds of argon in 2000, such as argon fluorohydride (HArF), and some bound to the late transition metals copper, silver, and gold.[32] As of 2007, no stable neutral molecules involving covalently bound helium or neon are known.[32]

The noble gases—including helium—can form stable molecular ions in the gas phase. The simplest is the helium hydride molecular ion, HeH+, discovered in 1925.[41] Because it is composed of the two most abundant elements in the universe, hydrogen and helium, it is believed to occur naturally in the interstellar medium, although it has not been detected yet.[42] In addition to these ions, there are many known neutral excimers of the noble gases. These are compounds such as ArF and KrF that are stable only when in an excited electronic state; some of them find application in excimer lasers.

In addition to the compounds where a noble gas atom is involved in a covalent bond, noble gases also form non-covalent compounds. The clathrates, first described in 1949,[43] consist of a noble gas atom trapped within cavities of crystal lattices of certain organic and inorganic substances. The essential condition for their formation is that the guest (noble gas) atoms must be of appropriate size to fit in the cavities of the host crystal lattice. For instance, argon, krypton, and xenon form clathrates with hydroquinone, but helium and neon do not because they are too small or insufficiently polarizable to be retained.[44] Neon, argon, krypton, and xenon also form clathrate hydrates, where the noble gas is trapped in ice.[45]

An endohedral fullerene compound containing a noble gas atom

Noble gases can form endohedral fullerene compounds, in which the noble gas atom is trapped inside a fullerene molecule. In 1993, it was discovered that when C60, a spherical molecule consisting of 60 carbon atoms, is exposed to noble gases at high pressure, complexes such as He@C60 can be formed (the @ notation indicates He is contained inside C60 but not covalently bound to it).[46] As of 2008, endohedral complexes with helium, neon, argon, krypton, and xenon have been obtained.[47] These compounds have found use in the study of the structure and reactivity of fullerenes by means of the nuclear magnetic resonance of the noble gas atom.[48]

Bonding in XeF2 according to the 3-center-4-electron bond model

Noble gas compounds such as xenon difluoride (XeF2) are considered to be hypervalent because they violate the octet rule. Bonding in such compounds can be explained using a 3-center-4-electron bond model.[49][50] This model, first proposed in 1951, considers bonding of three collinear atoms. For example, bonding in XeF2 is described by a set of three molecular orbitals (MOs) derived from p-orbitals on each atom. Bonding results from the combination of a filled p-orbital from Xe with one half-filled p-orbital from each F atom, resulting in a filled bonding orbital, a filled non-bonding orbital, and an empty antibonding orbital. The highest occupied molecular orbital is localized on the two terminal atoms. This represents a localization of charge which is facilitated by the high electronegativity of fluorine.[51]

The chemistry of heavier noble gases, krypton and xenon, are well established. The chemistry of the lighter ones, argon and helium, is still at an early stage, while a neon compound is still yet to be identified.

Occurrence and production

The abundances of the noble gases in the universe decrease as their atomic numbers increase. Helium is the most common element in the universe after hydrogen, with a mass fraction of about 24%. Most of the helium in the universe was formed during Big Bang nucleosynthesis, but the amount of helium is steadily increasing due to the fusion of hydrogen in stellar nucleosynthesis.[52][53] Abundances on Earth follow different trends; for example, helium is only the third most abundant noble gas in the atmosphere. The reason is that there is no primordial helium in the atmosphere; due to the small mass of the atom, helium cannot be retained by the Earth's gravitational field.[54] Helium on Earth comes from the alpha decay of heavy elements such as uranium and thorium found in the Earth's crust, and tends to accumulate in natural gas deposits.[54] The abundance of argon, on the other hand, is increased as a result of the beta decay of potassium-40, also found in the Earth's crust, to form argon-40, which is the most abundant isotope of argon on Earth despite being relatively rare in the Solar System. This process is the base for the potassium-argon dating method.[55] Xenon has an unexpectedly low abundance in the atmosphere, in what has been called the missing xenon problem; one theory is that the missing xenon may be trapped in minerals inside the Earth's crust.[56] Radon is formed in the lithosphere as from the alpha decay of radium. It can seep into buildings through cracks in their foundation and accumulate in areas that are not well ventilated. Due to its high radioactivity, radon presents a significant health hazard; it is implicated in an estimated 21,000 lung cancer deaths per year in the United States alone.[57]

Abundance Helium Neon Argon Krypton Xenon Radon
Solar System (for each atom of silicon)[58] 2343 2.148 0.1025 5.515 × 10−5 5.391 × 10−6 –
Earth's atmosphere (volume fraction in ppm)[59] 5.20 18.20 9340.00 1.10 0.09 (0.06 – 18) × 10−19[60]
Igneous rock (mass fraction in ppm)[24] 3 × 10−3 7 × 10−5 4 × 10−2 – – 1.7 × 10−10
Gas 2004 price (USD/m3)[61]
Helium (industrial grade) 4.20–4.90
Helium (laboratory grade) 22.30–44.90
Argon 2.70–8.50
Neon 60–120
Krypton 400–500
Xenon 4000–5000

Neon, argon, krypton, and xenon are obtained from air using the methods of liquefaction of gases, to convert elements to a liquid state, and fractional distillation, to separate mixtures into component parts. Helium is typically produced by separating it from natural gas, and radon is isolated from the radioactive decay of radium compounds.[11] The prices of the noble gases are influenced by their natural abundance, with argon being the cheapest and xenon the most expensive. As an example, the table to the right lists the 2004 prices in the United States for laboratory quantities of each gas.

Applications

Liquid helium is used to cool the superconducting magnets in modern MRI scanners.

Noble gases have very low boiling and melting points, which makes them useful as cryogenic refrigerants.[62] In particular, liquid helium, which boils at 4.2 K (−268.95 °C; −452.11 °F), is used for superconducting magnets, such as those needed in nuclear magnetic resonance imaging and nuclear magnetic resonance.[63] Liquid neon, although it does not reach temperatures as low as liquid helium, also finds use in cryogenics because it has over 40 times more refrigerating capacity than liquid helium and over three times more than liquid hydrogen.[60]

Helium is used as a component of breathing gases to replace nitrogen, due its low solubility in fluids, especially in lipids. Gases are absorbed by the blood and body tissues when under pressure like in scuba diving, which causes an anesthetic effect known as nitrogen narcosis.[64] Due to its reduced solubility, little helium is taken into cell membranes, and when helium is used to replace part of the breathing mixtures, such as in trimix or heliox, a decrease in the narcotic effect of the gas at depth is obtained.[65] Helium's reduced solubility offers further advantages for the condition known as decompression sickness, or the bends.[11][66] The reduced amount of dissolved gas in the body means that fewer gas bubbles form during the decrease in pressure of the ascent. Another noble gas, argon, is considered the best option for use as a drysuit inflation gas for scuba diving.[67]

The Spirit of Goodyear, one of the iconic Goodyear Blimps

Since the Hindenburg disaster in 1937,[68] helium has replaced hydrogen as a lifting gas in blimps and balloons due to its lightness and incombustibility, despite an 8.6%[69] decrease in buoyancy.[11]

In many applications, the noble gases are used to provide an inert atmosphere. Argon is used in the synthesis of air-sensitive compounds that are sensitive to nitrogen. Solid argon is also used for the study of very unstable compounds, such as reactive intermediates, by trapping them in an inert matrix at very low temperatures.[70] Helium is used as the carrier medium in gas chromatography, as a filler gas for thermometers, and in devices for measuring radiation, such as the Geiger counter and the bubble chamber.[61] Helium and argon are both commonly used to shield welding arcs and the surrounding base metal from the atmosphere during welding and cutting, as well as in other metallurgical processes and in the production of silicon for the semiconductor industry.[60]

15,000-watt xenon short-arc lamp used in IMAX projectors

Noble gases are commonly used in lighting because of their lack of chemical reactivity. Argon, mixed with nitrogen, is used as a filler gas for incandescent light bulbs.[60] Krypton is used in high-performance light bulbs, which have higher color temperatures and greater efficiency, because it reduces the rate of evaporation of the filament more than argon; halogen lamps, in particular, use krypton mixed with small amounts of compounds of iodine or bromine.[60] The noble gases glow in distinctive colors when used inside gas-discharge lamps, such as neon lights, which produce an orange-red color. Xenon is commonly used in xenon arc lamps which, due to their nearly continuous spectrum that resembles daylight, find application in film projectors and as automobile headlamps.[60]

The noble gases are used in excimer lasers, which are based on short-lived electronically excited molecules known as excimers. The excimers used for lasers may be noble gas dimers such as Ar2, Kr2 or Xe2, or more commonly, the noble gas is combined with a halogen in excimers such as ArF, KrF, XeF, or XeCl. These lasers produce ultraviolet light which, due to its short wavelength (193 nm for ArF and 248 nm for KrF), allows for high-precision imaging. Excimer lasers have many industrial, medical, and scientific applications. They are used for microlithography and microfabrication, which are essential for integrated circuit manufacture, and for laser surgery, including laser angioplasty and eye surgery.[71]

Some noble gases have direct application in medicine. Helium is sometimes used to improve the ease of breathing of asthma sufferers.[60] Xenon is used as an anesthetic because of its high solubility in lipids, which makes it more potent than the usual nitrous oxide, and because it is readily eliminated from the body, resulting in faster recovery.[72] Xenon finds application in medical imaging of the lungs through hyperpolarized MRI.[73] Radon, which is highly radioactive and is only available in minute amounts, is used in radiotherapy.[11]

Colors produced by different noble gases when used in neon tubes

Helium

Neon

Argon (with some mercury)

Krypton

Xenon

See also

  • Noble gas (data page), for extended tables of physical properties.
  • Noble metal, for metals that are resistant to corrosion or oxidation.
  • Inert gas, for any gas that is not reactive under normal circumstances.

Notes

  1. ^ See references given in Ununoctium (last sentence of the introduction)
  2. ^ See reference given in Ununquadium.
  3. ^ Renouf, Edward (1901-02-15). "Noble gases". Science 13: 268–270. doi:10.1126/science.13.320.268. 
  4. ^ Ozima 2002, p. 30
  5. ^ Ozima 2002, p. 4
  6. ^ "argon". Encyclopædia Britannica. 2008. http://www.britannica.com/eb/article-9009382/argon. 
  7. ^ Oxford English Dictionary (1989), s.v. "helium". Retrieved December 16, 2006, from Oxford English Dictionary Online. Also, from quotation there: Thomson, W. (1872). Rep. Brit. Assoc. xcix: "Frankland and Lockyer find the yellow prominences to give a very decided bright line not far from D, but hitherto not identified with any terrestrial flame. It seems to indicate a new substance, which they propose to call Helium."
  8. ^ a b Ozima 2002, p. 1
  9. ^ Mendeleev 1903, p. 497
  10. ^ Partington, J. R. (May 1957). "Discovery of Radon". Nature 179 (4566): 912. doi:10.1038/179912a0. 
  11. ^ a b c d e f g h i j "Noble Gas". Encyclopædia Britannica. 2008. http://www.britannica.com/eb/article-9110613/noble-gas. 
  12. ^ Cederblom, J. E. (1904). "The Nobel Prize in Physics 1904 Presentation Speech". http://nobelprize.org/nobel_prizes/physics/laureates/1904/press.html. 
  13. ^ a b Cederblom, J. E. (1904). "The Nobel Prize in Chemistry 1904 Presentation Speech". http://nobelprize.org/nobel_prizes/chemistry/laureates/1904/press.html. 
  14. ^ Gillespie, R. J.; Robinson, E. A. (January 2007). "Gilbert N. Lewis and the chemical bond: the electron pair and the octet rule from 1916 to the present day". J Comput Chem 28 (1): 87–97. doi:10.1002/jcc.20545. PMID 17109437. 
  15. ^ a b Bartlett, N. (1962). "Xenon hexafluoroplatinate Xe+[PtF6]–". Proceedings of the Chemical Society (6): 218. doi:10.1039/PS9620000197. 
  16. ^ Fields, Paul R.; Stein, Lawrence; Zirin, Moshe H. (1962). "Radon Fluoride". Journal of the American Chemical Society 84 (21): 4164–4165. doi:10.1021/ja00880a048. 
  17. ^ Grosse, A. V.; Kirschenbaum, A. D.; Streng, A. G.; Streng, L. V. (1963). "Krypton Tetrafluoride: Preparation and Some Properties". Science 139: 1047–1048. doi:10.1126/science.139.3559.1047. PMID 17812982. 
  18. ^ Khriachtchev, Leonid; Pettersson, Mika; Runeberg, Nino; Lundell, Jan; Räsänen, Markku (2000-08-24). "A stable argon compound". Nature 406 (406): 874–876. doi:10.1038/35022551. 
  19. ^ Oganessian, Yu. Ts. (1999). "Synthesis of Superheavy Nuclei in the 48Ca + 244Pu Reaction". Physical Review Letters (American Physical Society) 83: 3154. doi:10.1103/PhysRevLett.83.3154. 
  20. ^ Woods, Michael (2003-05-06). "Chemical element No. 110 finally gets a name—darmstadtium". Pittsburgh Post-Gazette. http://www.post-gazette.com/healthscience/20030506element0506p4.asp. Retrieved on 2008-06-26. 
  21. ^ "Gas Phase Chemistry of Superheavy Elements" (PDF). Texas A&M University. http://lch.web.psi.ch/files/lectures/TexasA&M/TexasA&M.pdf. Retrieved on 2008-05-31. 
  22. ^ Wilson, Elaine (2005). "Making Meaning in Chemistry Lessons". Electronic Journal of Literacy through Science 4 (2). 
  23. ^ Oganessian, Yu. Ts. (2006-10-09). "Synthesis of the isotopes of elements 118 and 116 in the 249Cf and 245Cm + 48Ca fusion reactions". Physical Review C 74 (4): 44602. doi:10.1103/PhysRevC.74.044602. 
  24. ^ a b c d Greenwood 1997, p. 891
  25. ^ Under pressure of 25 bar
  26. ^ "Solid Helium". University of Alberta. http://www.phys.ualberta.ca/~therman/lowtemp/projects1.htm. Retrieved on 2008-06-22. 
  27. ^ Wheeler, John C. (1997). "Electron Affinities of the Alkaline Earth Metals and the Sign Convention for Electron Affinity". Journal of Chemical Education 74: 123–127. ; Kalcher, Josef; Sax, Alexander F. (1994). "Gas Phase Stabilities of Small Anions: Theory and Experiment in Cooperation". Chemical Reviews 94: 2291–2318. doi:10.1021/cr00032a004. 
  28. ^ Mott, N. F. (1955). "John Edward Lennard-Jones. 1894-1954". Biographical Memoirs of Fellows of the Royal Society 1: 175–184. doi:10.1098/rsbm.1955.0013. 
  29. ^ "Scientists Announce Creation of Atomic Element, the Heaviest Yet". Washington Post. 2006-10-17. http://www.washingtonpost.com/wp-dyn/content/article/2006/10/16/AR2006101601083.html. Retrieved on 2008-06-26. 
  30. ^ Ozima 2002, p. 35
  31. ^ CliffsNotes 2007, p. 15
  32. ^ a b c d e f g h Grochala, Wojciech (2007). "Atypical compounds of gases, which have been called noble". Chemical Society Reviews 36 (36): 1632–1655. doi:10.1039/b702109g. 
  33. ^ Pauling, Linus (June 1933). "The Formulas of Antimonic Acid and the Antimonates". Journal of the American Chemical Society 55 (5): 1895–1900. doi:10.1021/ja01332a016. 
  34. ^ Holloway 1968
  35. ^ Seppelt, Konrad (June 1979). "Recent developments in the Chemistry of Some Electronegative Elements". Accounts of Chemical Research 12: 211–216. doi:10.1021/ar50138a004. 
  36. ^ Moody, G. J. (October 1974). "A Decade of Xenon Chemistry". Journal of Chemical Education 51 (10): 628–630. http://www.eric.ed.gov/ERICWebPortal/custom/portlets/recordDetails/detailmini.jsp?_nfpb=true&_&ERICExtSearch_SearchValue_0=EJ111480&ERICExtSearch_SearchType_0=no&accno=EJ111480. Retrieved on 2007-10-16. 
  37. ^ Zupan, Marko; Iskra, Jernej; Stavber, Stojan (1998). "Fluorination with XeF2. 44. Effect of Geometry and Heteroatom on the Regioselectivity of Fluorine Introduction into an Aromatic Ring". J. Org. Chem 63 (3): 878–880. doi:10.1021/jo971496e. 
  38. ^ Harding 2002, pp. 90–99
  39. ^ .Avrorin, V. V.; Krasikova, R. N.; Nefedov, V. D.; Toropova, M. A. (1982). "The Chemistry of Radon". Russian Chemical Review 51 (1): 12–20. doi:10.1070/RC1982v051n01ABEH002787. 
  40. ^ http://dx.doi.org/10.1016/S0010-8545(02)00202-3 doi:10.1016/S0010-8545(02)00202-3
  41. ^ Hogness, T. R.; Lunn, E. G. (1925). "The Ionization of Hydrogen by Electron Impact as Interpreted by Positive Ray Analysis". Physical Review 26: 44–55. doi:10.1103/PhysRev.26.44. 
  42. ^ Fernandez, J.; Martin, F. (2007). "Photoionization of the HeH2+ molecular ion". J. Phys. B: At. Mol. Opt. Phys 40: 2471–2480. doi:10.1088/0953-4075/40/12/020. 
  43. ^ H. M. Powell and M. Guter (1949). "An Inert Gas Compound". Nature 164: 240–241. doi:10.1038/164240b0. 
  44. ^ Greenwood 1997, p. 893
  45. ^ Yuri A. Dyadin, Eduard G. Larionov, Andrei Yu. Manakov, Fridrich V. Zhurko, Evgeny Ya. Aladko, Tamara V. Mikina, Vladislav Yu. Komarov (1999). "Clathrate hydrates of hydrogen and neon". Mendeleev Communications 9 (5): 209–210. doi:10.1070/MC1999v009n05ABEH001104. 
  46. ^ Saunders, M.; Jiménez-Vázquez, H. A.; Cross, R. J.; Poreda, R. J. (1993). "Stable compounds of helium and neon. He@C60 and Ne@C60". Science 259: 1428–1430. doi:10.1126/science.259.5100.1428. PMID 17801275. 
  47. ^ Saunders, Martin; Jimenez-Vazquez, Hugo A.; Cross, R. James; Mroczkowski, Stanley; Gross, Michael L.; Giblin, Daryl E.; Poreda, Robert J. (1994). "Incorporation of helium, neon, argon, krypton, and xenon into fullerenes using high pressure". J. Am. Chem. Soc. 116 (5): 2193–2194. doi:10.1021/ja00084a089. 
  48. ^ Frunzi, Michael; Cross, R. James; Saunders, Martin (2007). "Effect of Xenon on Fullerene Reactions". Journal of the American Chemical Society 129: 13343. doi:10.1021/ja075568n. 
  49. ^ Greenwood 1997, p. 897
  50. ^ Weinhold 2005, pp. 275–306
  51. ^ Pimentel, G. C. (1951). "The Bonding of Trihalide and Bifluoride Ions by the Molecular Orbital Method". The Journal of Chemical Physics 19 (4): 446–448. doi:10.1063/1.1748245. 
  52. ^ Weiss, Achim. "Elements of the past: Big Bang Nucleosynthesis and observation". Max Planck Institute for Gravitational Physics. http://www.einstein-online.info/en/spotlights/BBN_obs/index.html. Retrieved on 2008-06-23. 
  53. ^ Coc, A.; et al. (2004). "Updated Big Bang Nucleosynthesis confronted to WMAP observations and to the Abundance of Light Elements". Astrophysical Journal 600: 544. doi:10.1086/380121. 
  54. ^ a b Morrison, P.; Pine, J. (1955). "Radiogenic Origin of the Helium Isotopes in Rock". Annals of the New York Academy of Sciences 62 (3): 71–92. doi:10.1111/j.1749-6632.1955.tb35366.x. 
  55. ^ Scherer, Alexandra (2007-01-16). "40Ar/39Ar dating and errors". Technische Universität Bergakademie Freiberg. http://www.geoberg.de/text/geology/07011601.php. Retrieved on 2008-06-26. 
  56. ^ Sanloup, Chrystèle; et al. (2005). "Retention of Xenon in Quartz and Earth's Missing Xenon". Science 310 (5751): 1174–1177. doi:10.1126/science.1119070. PMID 16293758. 
  57. ^ "A Citizen's Guide to Radon". U.S. Environmental Protection Agency. 2007-11-26. http://www.epa.gov/radon/pubs/citguide.html. Retrieved on 2008-06-26. 
  58. ^ Lodders, Katharina (2003). "Solar System Abundances and Condensation Temperatures of the Elements". The Astrophysical Journal 591: 1220–1247. doi:10.1086/375492. 
  59. ^ "The Atmosphere". National Weather Service. http://www.srh.noaa.gov/jetstream//atmos/atmos_intro.htm. Retrieved on 2008-06-01. 
  60. ^ a b c d e f g Häussinger, Peter; Glatthaar, Reinhard; Rhode, Wilhelm; Kick, Helmut; Benkmann, Christian; Weber, Josef; Wunschel, Hans-Jörg; Stenke, Viktor; Leicht, Edith; Stenger, Hermann (2002). "Noble gases". Ullmann's Encyclopedia of Industrial Chemistry. Wiley. doi:10.1002/14356007.a17_485. 
  61. ^ a b Hwang, Shuen-Chen; Lein, Robert D.; Morgan, Daniel A. (2005). "Noble Gases". Kirk Othmer Encyclopedia of Chemical Technology. Wiley. pp. 343–383. doi:10.1002/0471238961.0701190508230114.a01. 
  62. ^ "Neon". Encarta. 2008. 
  63. ^ Zhang, C. J.; Zhou, X. T.; Yang, L. (January 1992). "Demountable coaxial gas-cooled current leads for MRI superconducting magnets". Magnetics, IEEE Transactions on (IEEE) 28 (1): 957–959. doi:10.1109/20.120038. 
  64. ^ Fowler, B; Ackles, K. N.; Porlier, G. (1985). "Effects of inert gas narcosis on behavior—a critical review". Undersea Biomed. Res. 12 (4): 369–402. ISSN 0093-5387. OCLC 2068005. PMID 4082343. http://archive.rubicon-foundation.org/3019. Retrieved on 2008-04-08. 
  65. ^ Bennett 1998, p. 176
  66. ^ Vann, R. D. (ed) (1989). "The Physiological Basis of Decompression". 38th Undersea and Hyperbaric Medical Society Workshop 75(Phys)6-1-89: 437. http://archive.rubicon-foundation.org/6853. Retrieved on 2008-05-31. 
  67. ^ Maiken, Eric (2004-08-01). "Why Argon?". Decompression. http://www.decompression.org/maiken/Why_Argon.htm. Retrieved on 2008-06-26. 
  68. ^ "Disaster Ascribed to Gas by Experts". The New York Times: p. 1. 1937-05-07. 
  69. ^ Freudenrich, Craig (2008). "How Blimps Work". HowStuffWorks. http://science.howstuffworks.com/blimp2.htm. Retrieved on 2008-07-03. 
  70. ^ Dunkin, I. R. (1980). "The matrix isolation technique and its application to organic chemistry". Chem. Soc. Rev. 9: 1–23. doi:10.1039/CS9800900001. 
  71. ^ Basting, Dirk; Marowsky, Gerd (2005). Excimer Laser Technology. Springer. ISBN 3540200568. 
  72. ^ Sanders, Robert D.; Ma, Daqing; Maze, Mervyn (2005). "Xenon: elemental anaesthesia in clinical practice". British Medical Bulletin 71 (1): 115–135. doi:10.1093/bmb/ldh034. PMID 15728132. 
  73. ^ Albert, M. S.; Balamore, D. (1998). "Development of hyperpolarized noble gas MRI". Nuclear Instruments and Methods in Physics Research A 402: 441–453. doi:10.1016/S0168-9002(97)00888-7. http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=11543065&dopt=AbstractPlus. Retrieved on 2007-10-01. 

References

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