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Fluorine (F)

Fluorine

History

Fluorine is a very pale yellow-green, dangerously reactive gas. It is the most reactive of all the elements and quickly attacks all metals. Steel wool bursts into flames when exposed to fluorine.

The element is used to make uranium hexafluoride, needed by the nuclear power industry to separate uranium isotopes. It is also used to make sulfur hexafluoride, the insulating gas for high-power electricity transformers.

CFCs (chloro-fluoro-carbons) were once used as aerosol propellants, refrigerants and for ‘blowing’ expanded polystyrene. However, their inertness meant that, once in the atmosphere, they diffused into the stratosphere and destroyed the Earth’s ozone layer. They are now banned.

Did you know?

  1. There was no commercial production of fluorine until the Second World War, when the development of the atom bomb, and other nuclear energy projects, made it necessary to produce large quantities. Before this, fluorine salts, known as fluorides, were for a long time used in welding and for frosting glass.
  2. Hydrofluoric acid is used for etching the glass of light bulbs and in similar applications.
  3. Fluorine is used in many fluorochemicals, including solvents and high-temperature plastics, such as Teflon (poly(tetrafluoroethene), PTFE). Teflon is well known for its non-stick properties and is used in frying pans. It is also used for cable insulation, for plumber’s tape and as the basis of Gore-Tex® (used in waterproof shoes and clothing).
  • Atomic Properties
    Atomic number 9
    Atomic radius - Goldschmidt ( nm ) 0.071
    Atomic weight ( amu ) 19.00
    Electronic structure He 2s2 p5
    Ionisation potential No. eV
    1 17.42
    2 34.97
    3 62.70
    4 87.14
    5 114.24
    6 157.61
    Natural isotope distribution Mass No. %
    19 100
    Thermal neutron absorption cross-section ( Barns ) 0.0048
    Valences shown -1
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Chlorine (Cl)

Chlorine

History

Chlorine is not found uncombined in nature. Halite (sodium chloride or ‘common salt’) is the main mineral that is mined for chlorine. Sodium chloride is a very soluble salt that has been leached into the oceans over the lifetime of the Earth. Several salt beds, or ‘lakes’ are found where ancient seas have evaporated, and these can be mined for chloride.

Chlorine is also found in the minerals carnallite (magnesium potassium chloride) and sylvite (potassium chloride).

40 million tonnes of chlorine gas are made each year from the electrolysis of brine (sodium chloride solution). This process also produces useful sodium hydroxide.

Did you know?

  1. A major use for chlorine is in organic chemistry. It is used as an oxidising agent and in substitution reactions. 85% of pharmaceuticals use chlorine or its compounds at some stage in their manufacture.
  2. In the past chlorine was commonly used to make chloroform (an anaesthetic) and carbon tetrachloride (a dry-cleaning solvent). However, both of these chemicals are now strictly controlled as they can cause liver damage.
  3. Chlorine gas is itself very poisonous, and was used as a chemical weapon during the First World War.
  • Atomic Properties
    Atomic number 17
    Atomic radius - Goldschmidt ( nm ) 0.107
    Atomic weight ( amu ) 35.453
    Electronic structure Ne 3s2 p5
    Ionisation potential No. eV
    1 12.97
    2 23.81
    3 39.63
    4 53.46
    5 67.8
    6 97.03
    Natural isotope distribution Mass No. %
    35 75.77
    37 24.23
    Valences shown ±1, 3, 5, 7
  • Physical Properties
    Boiling point ( C ) -34.6
    Density @27C ( g cm-3 ) 0.00317
    Melting point ( C ) -100.98
  • Thermal Properties
    Latent heat of evaporation ( J g-1 ) 288.2
    Latent heat of fusion ( J g-1 ) 90.5
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Bromine (Br)

Bromine

History

Bromine is a deep-red, oily liquid with a sharp smell. It is toxic. Bromine is extracted by electrolysis from natural bromine-rich brine deposits in the USA, Israel and China. It was the first element to be extracted from seawater, but this is now only economically viable at the Dead Sea, Israel, which is particularly rich in bromide (up to 0.5%).

Bromine is used in many areas such as agricultural chemicals, dyestuffs, insecticides, pharmaceuticals and chemical intermediates. Some uses are being phased out for environmental reasons, but new uses continue to be found.

Did you know?

  1. Bromine compounds can be used as flame retardants. They are added to furniture foam, plastic casings for electronics and textiles to make them less flammable. However, the use of bromine as a flame retardant has been phased out in the USA because of toxicity concerns.
  2. Organobromides are used in halon fire extinguishers that are used to fight fires in places like museums, aeroplanes and tanks. Silver bromide is a chemical used in film photography.
  3. Before leaded fuels were phased out, bromine was used to prepare 1,2-di-bromoethane, which was an anti-knock agent.
  • Atomic Properties
    Atomic number 35
    Atomic radius - Goldschmidt ( nm ) 0.119
    Atomic weight ( amu ) 79.904
    Electronic structure Ar 3d1O 4s2 p5
    Ionisation potential No. eV
    1 11.814
    2 21.8
    3 36.0
    4 47.3
    5 59.7
    6 88.6
    Natural isotope distribution Mass No. %
    79 50.69
    81 49.31
    Thermal neutron absorption cross-section ( Barns ) 6.8
    Valences shown ± 1, 5
  • Electrical Properties
    Electrical resistivity @20 6.5 1015C ( µOhmcm ) 6.5 1015
  • Physical Properties
    Boiling point ( C ) 58.78
    Density @20C ( g cm-3 ) 3.12
    Melting point ( C ) -7.2
  • Thermal Properties
    Latent heat of evaporation ( J g-1 ) 184.3
    Latent heat of fusion ( J g-1 ) 66.14
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Iodine (I)

Iodine

History

Iodine is found in seawater, as iodide. It is only present in trace amounts (0.05 parts per million); however, it is assimilated by seaweeds. In the past iodine was obtained from seaweed.

Now the main sources of iodine are iodate minerals, natural brine deposits left by the evaporation of ancient seas and brackish (briny) waters from oil and salt wells.

Iodine is obtained commercially by releasing iodine from the iodate obtained from nitrate ores or extracting iodine vapour from the processed brine.

Did you know?

  1. Photography was the first commercial use for iodine after Louis Daguerre, in 1839, invented a technique for producing images on a piece of metal. These images were called daguerreotypes.
  2. Today, iodine has many commercial uses. Iodide salts are used in pharmaceuticals and disinfectants, printing inks and dyes, catalysts, animal feed supplements and photographic chemicals. Iodine is also used to make polarising filters for LCD displays.
  3. Iodide is added in small amounts to table salt, in order to avoid iodine deficiency affecting the thyroid gland. The radioactive isotope iodine-131 is sometimes used to treat cancerous thyroid glands.
  • Atomic Properties
    Atomic number 53
    Atomic radius - Goldschmidt ( nm ) 0.138
    Atomic weight ( amu ) 126.9
    Electronic structure Kr 4d1O 5s2 p5
    Ionisation potential No. eV
    1 10.45
    2 19.13
    3 33.0
    Natural isotope distribution Mass No. %
    127 100
    Thermal neutron absorption cross-section ( Barns ) 6.2
    Valences shown ±1, 5, 7
  • Thermal Properties
    Latent heat of evaporation ( J g-1 ) 164.6
    Latent heat of fusion ( J g-1 ) 61.1
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Astatine (At)

Astatine

History

According to the Royal Society of Chemistry, in 1939, two groups came near to discovering this element in mineral samples. Horia Hulubei and Yvette Cauchois analysed mineral samples using a high-resolution X-ray apparatus and thought they had detected it. Meanwhile, Walter Minder observed the radioactivity of radium and said it appeared have another element present. He undertook chemical tests which suggested it was like iodine.

Element 85 was convincingly produced for the first time at the University of California in 1940 by Dale R. Corson, K.R. Mackenzie, and Emilio Segré. Their astatine was made by bombarding bismuth with alpha particles. Although they reported their discovery, they were unable to carry on with their research due to World War II and the demands of the Manhattan project which diverted all researchers of radioactive materials towards the making of nuclear weapons.

Did you know?

  1. There are currently no uses for astatine outside of research. The half-life of the most stable isotope is only 8 hours, and only tiny amounts have ever been produced.
  2. A mass spectrometer has been used to confirm that astatine behaves chemically like other halogens, particularly iodine.
  3. Astatine can be obtained in a variety of ways, but not in weighable amounts. Astatine-211 is made in nuclear reactors by the neutron bombardment of bismuth-200.
  • Atomic Properties
    Atomic number 85
    Atomic weight ( amu ) (210)
    Electronic structure Xe 4f14 5d1O 6s2 p5
    Valences shown ±1, 3, 5, 7
  • Physical Properties
    Boiling point ( C ) 337
    Melting point ( C ) 302
  • Thermal Properties
    Latent heat of evaporation ( J g-1 ) 380.9
    Latent heat of fusion ( J g-1 ) 113.3