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Helium (He)

helium

History

In 1868, Pierre J. C. Janssen travelled to India to measure the solar spectrum during a total eclipse and observed a new yellow line which indicated a new element. Joseph Norman Lockyer recorded the same line by observing the sun through London smog and, assuming the new element to be a metal, he named it helium.

In 1882, the Italian Luigi Palmieri found the same line the spectrum of gases emitted by Vesuvius, as did the American William Hillebrand in 1889 when he collected the gas given off by the mineral uraninite (UO2) as it dissolves in acid. However, it was Per Teodor Cleve and Nils Abraham Langer at Uppsala, Sweden, in 1895, who repeated that experiment and confirmed it was helium and measured its atomic weight.

Did you know?

  1. The name is derived from the Greek, 'helios' meaning sun, as it was in the sun's corona that helium was first detected.
  2. After hydrogen, helium is the second most abundant element in the universe. It is present in all stars. It was, and is still being, formed from alpha-particle decay of radioactive elements in the Earth. Some of the helium formed escapes into the atmosphere, which contains about 5 parts per million by volume. This is a dynamic balance, with the low-density helium continually escaping to outer space.
  3. It is uneconomical to extract helium from the air. The major source is natural gas, which can contain up to 7% helium.
  • Atomic Properties
    Atomic number 10
    Atomic radius - Goldschmidt ( nm ) 0.158
    Atomic weight ( amu ) 20.18
    Electronic structure He 2s2 p6
    Ionization potential No. eV
    1 21.56
    2 40.96
    3 63.45
    4 97.11
    5 126.21
    6 157.93
    Natural isotope distribution Mass No. %
    20
    21
    22
    Valences shown 0
  • Physical Properties
    Boiling point ( C ) -246.05
    Melting point ( C ) -248.67
  • Thermal Properties
    Latent heat of evaporation ( J g-1 ) 88.5
    Latent heat of fusion ( J g-1 ) 17
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Neon (Ne)

neon

History

Neon is a colourless, odourless gas. Neon will not react with any other substance. Neon is the fifth most abundant element in the universe. However, it is present in the Earth’s atmosphere at a concentration of just 18 parts per million. It is extracted by fractional distillation of liquid air. This gives a fraction that contains both helium and neon. The helium is removed from the mixture with activated charcoal.

Did you know?

  1. The largest use of neon is in making the ubiquitous ‘neon signs’ for advertising. In a vacuum discharge tube neon glows a reddish orange colour. Only the red signs actually contain pure neon. Others contain different gases to give different colours.
  2. Neon is also used to make high-voltage indicators and switching gear, lightning arresters, diving equipment and lasers.
  3. Liquid neon is an important cryogenic refrigerant. It has over 40 times more refrigerating capacity per unit volume than liquid helium, and more than 3 times that of liquid hydrogen.
  • Atomic Properties
    Atomic number 10
    Atomic radius - Goldschmidt ( nm ) 0.158
    Atomic weight ( amu ) 20.18
    Electronic structure He 2s2 p6
    Ionization potential No. eV
    1 21.56
    2 40.96
    3 63.45
    4 97.11
    5 126.21
    6 157.93
    Natural isotope distribution Mass No. %
    20
    21
    22
    Valences shown 0
  • Physical Properties
    Boiling point ( C ) -246.05
    Melting point ( C ) -248.67
  • Thermal Properties
    Latent heat of evaporation ( J g-1 ) 88.5
    Latent heat of fusion ( J g-1 ) 17.0
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Argon (Ar)

argon

History

Argon makes up 0.94% of the Earth’s atmosphere and is the third most abundant atmospheric gas. Levels have gradually increased since the Earth was formed because radioactive potassium-40 turns into argon as it decays. Argon is obtained commercially by the distillation of liquid air.

Did you know?

  1. Argon is often used when an inert atmosphere is needed. It is used in this way for the production of titanium and other reactive elements. It is also used by welders to protect the weld area and in incandescent light bulbs to stop oxygen from corroding the filament.
  2. Argon is used in fluorescent tubes and low-energy light bulbs. A low-energy light bulb often contains argon gas and mercury. When it is switched on an electric discharge passes through the gas, generating UV light. The coating on the inside surface of the bulb is activated by the UV light and it glows brightly.
  3. Double-glazed windows use argon to fill the space between the panes. The tyres of luxury cars can contain argon to protect the rubber and reduce road noise.
  • Atomic Properties
    Atomic number 18
    Atomic radius - Goldschmidt ( nm ) 0.191
    Atomic weight ( amu ) 39.948
    Electronic structure Ne 3s2 p6
    Ionization potential No. eV
    1 15.759
    2 27.629
    3 40.74
    4 59.81
    5 75.02
    6 91.01
    Natural isotope distribution Mass No. %
    36
    38
    40
    Valences shown 0
  • Physical Properties
    Boiling point ( C ) -185.7
    Density @20C ( g cm-3 ) 0.001784
    Melting point ( C ) -189.2
  • Thermal Properties
    Latent heat of evaporation ( J g-1 ) 162.8
    Latent heat of fusion ( J g-1 ) 19.74
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Krypton (Kr)

Krypton

About

Krypton is one of the rarest gases in the Earth’s atmosphere. It makes up just 1 part per million by volume. It is extracted by distillation of air that has been cooled until it is a liquid. Krypton is a gas with no colour or smell. It does not react with anything except fluorine gas.

Did you know?

  1. Krypton is used commercially as a filling gas for energy-saving fluorescent lights. It is also used in some flash lamps used for high-speed photography.
  2. Unlike the lighter gases in its group, it is reactive enough to form some chemical compounds. For example, krypton will react with fluorine to form krypton fluoride. Krypton fluoride is used in some lasers.
  3. Radioactive krypton was used during the Cold War to estimate Soviet nuclear production. The gas is a product of all nuclear reactors, so the Russian share was found by subtracting the amount that came from Western reactors from the total in the air.
  • Atomic Properties
    Atomic number 36
    Atomic weight ( amu ) 83.8
    Electronic structure Ar 3d1O 4s2 p6
    Ionization potential No. eV
    1 14.0
    2 24.34
    3 36.95
    4 52.5
    5 64.7
    6 78.5
    Natural isotope distribution Mass No. %
    78 0.35
    80 0.25
    82 11.6
    83 11.5
    84 57.9
    86 17.3
    Thermal neutron absorption cross-section ( Barns ) 24.5
    Valences shown 0
  • Physical Properties
    Boiling point ( C ) -152.3
    Density @20C ( g cm-3 ) 0.00374
    Melting point ( C ) -156.6
  • Thermal Properties
    Latent heat of evaporation ( J g-1 ) 107.7
    Latent heat of fusion ( J g-1 ) 19.57
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Xenon (Xe)

Xenon

History

Xenon is a colourless, odourless gas. It is very unreactive. Xenon has no known biological role. It is not itself toxic, but its compounds are highly toxic because they are strong oxidising agents.

Xenon is present in the atmosphere at a concentration of 0.086 parts per million by volume. It can also be found in the gases that evolve from certain mineral springs. It is obtained commercially by extraction from liquid air.

Did you know?

  1. Xenon is used in certain specialised light sources. It produces a beautiful blue glow when excited by an electrical discharge. Xenon lamps have applications as high-speed electronic flash bulbs used by photographers, sunbed lamps and bactericidal lamps used in food preparation and processing. Xenon lamps are also used in ruby lasers.
  2. Xenon ion propulsion systems are used by several satellites to keep them in orbit, and in some other spacecraft.
  3. Xenon difluoride is used to etch silicon microprocessors. It is also used in the manufacture of 5-fluorouracil, a drug used to treat certain types of cancer.
  • Atomic Properties
    Atomic number 54
    Atomic radius - Goldschmidt ( nm ) 0.218
    Atomic weight ( amu ) 131.29
    Electronic structure Kr 4d1O 5s2 p6
    Ionization potential No. eV
    1 12.13
    2 21.29
    3 32.1
    Natural isotope distribution Mass No. %
    129 26.4
    130 4.1
    131 21.2
    132 26.9
    134 10.4
    136 8.9
  • Physical Properties
    Boiling point ( C ) -107
    Density @20C ( g cm-3 ) 0.0059
    Melting point ( C ) -111.9
  • Thermal Properties
    Latent heat of evaporation ( J g-1 ) 96.3
    Latent heat of fusion ( J g-1 ) 17.5
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Radon (Rn)

Radon

History

Radon is a colourless and odourless gas. It is chemically inert, but radioactive.

In 1899, Ernest Rutherford and Robert B. Owens detected a radioactive gas being released by thorium. That same year, Pierre and Marie Curie detected a radioactive gas emanating from radium. In1900, Friedrich Ernst Dorn at Halle, Germany, noted that a gas was accumulating inside ampoules of radium. They were observing radon. That from radium was the longer-lived isotope radon-222 which has a half-life 3.8 days, and was the same isotope which the Curies has observed. The radon that Rutherford detected was radon-220 with a half-life of 56 seconds.

In 1900, Rutherford devoted himself to investigating the new gas and showed that it was possible to condense it to a liquid. In 1908, William Ramsay and Robert Whytlaw-Gray at University College, London, collected enough radon to determine its properties and reported that it was the heaviest gas known.

Did you know?

  1. Radon decays into radioactive polonium and alpha particles. This emitted radiation made radon useful in cancer therapy. Radon was used in some hospitals to treat tumours by sealing the gas in minute tubes, and implanting these into the tumour, treating the disease in situ. Other, safer treatments are now more commonly used.
  2. In some places, high concentrations of radon can build up indoors, escaping from the ground or from granite buildings. Home testing kits are available which can be sent away for analysis.
  3. Radon has no known biological role. It is, however, thought that it may have had a significant role in evolution. This is because it is responsible for much of the Earth’s background radiation that can lead to genetic modifications.
  • Atomic Properties
    Atomic number 86
    Atomic radius - Goldschmidt ( nm ) 0.132
    Atomic weight ( amu ) (222)
    Electronic structure Xe 4f14 5d1O
    Ionization potential No. eV
    1 10.75
    Valences shown 0
  • Physical Properties
    Boiling point ( C ) -61.8
    Density @27C ( g cm-3 ) 0.0099
    Melting point ( C ) -71
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Oganesson (Og)

oganesson

History

The Danish physicist Niels Bohr was the first to seriously consider the possibility of an element with atomic number as high as 118, noting in 1922 that such an element would take its place in the periodic table below radon as the seventh noble gas.

Following this, Aristid von Grosse wrote an article in 1965 predicting the likely properties of element 118. These were remarkably early predictions, given that it was not yet known how to produce elements artificially in 1922, and that the existence of the island of stability had not yet been theorized in 1965.

It took eighty years from Bohr's initial prediction before oganesson was first successfully synthesised, although its chemical properties have not yet been investigated to see if it really does behave as the heavier congener of radon.

Did you know?

  1. The radioactive oganesson atom is very unstable, and since 2005, only four atoms of the isotope 294Og have been detected.
  2. It was first synthesized in 2002 by a joint team of Russian and American scientists at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia. In December 2015, it was recognized as one of four new elements by the Joint Working Party of international scientific bodies IUPAC and IUPAP. It was formally named on 28 November 2016.
  • Atomic Properties
    Atomic number 118