8A Group 8A GROUP 8A Ne
Group 8A
Group 8A
The names of all the noble gases except radon come from Greek words. Helium comes from helios, meaning "sun." Xenon comes from xenos, meaning "strange." Krypton comes from kryptos, meaning "hidden." Argon comes from argos, meaning "inert." Neon comes from neos, or "new."
Physical and Chemical Properties
More than 80 compounds of xenon have been produced. Krypton forms the colorless solid krypton(II) fluoride, KrF2. The compound of argon, argon fluorohydride (HArF), produced in 2000 exists only at temperatures below -246?C.
To Do
Show students how to draw an electron dot structure for xenon(II) fluoride (XeF2). Then have students draw electron dot structures for xenon(IV) fluoride (XeF4), xenon(IV) oxide (XeO3), and xenon(VIII) oxide (XeO4). As a further challenge, students could try drawing the electron dot structures for XeO2F2 or XeOF4.
Sources
Although there are measurable amounts of radon in most regions of the United States, the highest levels are recorded in regions where the bedrock is granite. Radon is a product of the natural decay of uranium238. Radon can seep through cracks in foundations and basements floors. Because it is denser than air, radon tends to collect in the lower levels of a house. Inhaling radon may increase the risk of lung cancer. High levels of radon can be reduced by improved ventilation in basements and other closed areas where radon collects.
8A GROUP
22
He
Helium 4.0026
Helium discovered in 1868 by Pierre Janssen
10
2 8
Ne
Neon 20.179
Neon discovered in 1898 by Sir William Ramsay & Morris Travers
18
2 8
Ar 8
Argon 39.948
Argon discovered in 1894 by Lord Rayleigh & Sir William Ramsay
36
2 8
Kr 18 8
Krypton 83.80
Krypton discovered in 1898 by Sir William Ramsay & Morris Travers
54
2 8
Xe 18 18 8
Xenon
131.30
Xenon discovered in 1898 by Sir William Ramsay & Morris Travers
86
2 8
Rn 18 32 18
Radon 8
(222)
Radon discovered in 1900 by Friedrich E. Dorn
Sources
r Helium is separated from natural gas deposits. Neon, argon, krypton, and xenon are separated from air by fractional distillation.
r Because of its low density, helium is used in weather balloons and airships.
r In addition to "neon" lights, noble gases are used in fluorescent bulbs, strobe lights, and headlights.
r Liquid helium cools the magnets used for magnetic resonance imaging (MRI).
R32 Elements Handbook
Temperature (C) Density (g/L)*
Physical and Chemical Properties
r All Group 8A elements are monatomic gases at STP.
r Noble gases are colorless, odorless, and tasteless.
r The first compound of a noble gas, XePtF6, was made in 1962. More than 100 compounds of fluorine and xenon are now known.
Incandescent light bulbs are filled with argon instead of air to extend the life of the filament.
r A compound of argon, HArF, exists only at temperatures below 246?C.
Melting and Boiling Points
0
- 70 - 140 - 210 - 280
?62 ?108 ?71 ?153 ?112
?186 ?157
?189
?246
bp
?269 ?249
mp
?272
He Ne Ar Kr Xe Rn
Density
10.0
9.73
7.5
5.90
5.0
3.75
2.5
1.78
0.18 0.90 0
He Ne Ar Kr Xe Rn
*at STP
Atomic Properties
r Noble gases have an electron configuration that ends in ns2np6, except for helium (1s2).
r In noble gas compounds, the most common oxidation number for the gas is ?2.
r Noble gases have the highest ionization energies because their energy levels are filled.
Energy (kJ/mol)
First Ionization Energy
2400 1800 1200
2372 2080 1520 1351 1170 1037
600
0
He Ne Ar Kr Xe Rn
Helium Neon
Argon
Krypton
Xenon
Each noble gas emits a characteristic color in a gas discharge tube.
0132525763_R32-R33.indd 32
Atomic Properties
The noble gases that form compounds most readily have larger atoms in which there are more electrons to shield the electrons in the highest occupied energy level from the nuclear charge.
To Do
Encourage students to research the role of krypton-86 in the development of a definition for a meter. Ask them to determine why a definition based on krypton-86 was adopted in 1960 and why it was replaced in 1983.
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R32 Elements Handbook
Group 8A
Ne Neon Lights
By 1855, scientists could produce light by passing an electric current through a gas under low pressure in a sealed glass tube. With the discovery of the noble gases, a new technology emerged. In 1910, George Claude displayed the first neon lamp in Paris, France.
In 1923, a car dealer from Los Angeles bought two signs that spelled out "Packard" for $24,000 (about $250,000 in today's dollars). When he displayed the signs in Los Angeles, people described the light as "liquid fire." By the 1930s, businesses were using neon lights to draw the attention of customers.
Neon and argon are the gases most often used in neon lights. Orangered lights contain only neon. Other colors are produced by adding a bit of mercury to the noble gas. The tube is coated with a material that glows when exposed to UV light emitted by mercury vapor.
Ar Taken For a Ride By Argon
Whether riding on a paved city street or on an unpaved mountain trail, a bicyclist is likely to find rough patches. When faced with rough terrain, the cyclist may worry about the tires, but probably not about the bicycle frame. The metal frames are made of steel, aluminum alloy, or titanium tubes that are joined together.
The tubes are joined together by Tungsten Inert Gas (TIG) welding. An electric arc is struck between a tungsten electrode and the parts to be welded. Heat from the arc melts the ends of the tubes and fuses them together. Filler may be placed between the ends of the tubes to increase the strength of the joint or to produce a smoother joint.
During welding in air, there is a danger that the metal tubes or electrode will oxidize. To prevent oxidation, the area around the arc is filled with an inert gas, most often argon. Welding with argon has an added benefit. Because argon is a poor conductor of heat, the arc that forms is narrow. This narrow arc produces a weld that is both neat in appearance and mechanically strong.
Xe Xenon-Ion Engine
The signals for a television program may bounce off a communication satellite. The satellite is in orbit above the equator. The position of the satellite may be maintained by a xenon-ion propulsion system.
When electrons strike xenon atoms in a xenon-ion engine, the atoms lose electrons and form positive ions. The ions are accelerated by a charged grid and shot from the engine at about 105 km/h. This action pushes, or thrusts, the satellite in the opposite direction. With multiple engines facing in different directions, a satellite can be moved in any direction.
Although a xenon-ion engine produces a relatively small amount of thrust, it can provide thrust for months or years. This makes xenon-ion engines a good choice for lengthy space missions. In addition, an inert gas poses no hazard for the satellite or the people who handle the propellant tanks.
Did You Know?
When liquid helium is cooled to below 2 K, its viscosity drops to zero. It will escape from an unsealed container by flowing up the sides of the container.
Group 8A R33
Ne Neon Lights
The development of neon lights can be traced back to an observation made by the French astronomer Jean Picard in 1675. He observed a faint glow in the tube of a mercury barometer when the tube was shaken.
Los Angeles in the 1930s was a low-rise city. Businesses used elaborate, art deco neon signs to attract motorists, who could see the signs from miles away. Many of the vintage signs have been restored. In 1949, Raymond Chandler wrote, "There ought to be a monument to the man who invented neon lights." (A monument to Claude might be a problem given his political choices. He was imprisoned from 1945?1949 for his support of the Vichy government in occupied France.)
Xe Xenon-Ion Engines
Because it completes one orbit in 24 hours, a communication satellite appears to be stationary above Earth. The altitude at which a satellite orbits Earth depends on its task. Stationary weather and communication satellites orbit at an altitude of about 22,300 miles. The region in which they orbit is called the Clarke Belt in honor of the science-fiction writer Arthur C. Clarke. Countries are assigned positions in the Clarke Belt for their communications and weather satellites.
Ar Taken For a Ride By Argon
Welders who use TIG must be aware of a safety issue. Breathing argon-rich air can deprive the body of oxygen. A person could pass out or even die from asphyxiation. So argon must be used in a wellventilated room.
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Group 8A R33
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