   #copyright

Argon

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                18              chlorine ← argon → potassium
                Ne
                ↑
                Ar
                ↓
                Kr

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                        Name, Symbol, Number argon, Ar, 18
                                               Chemical series noble gases
                                             Group, Period, Block 18, 3, p
                                                      Appearance colorless
                                              Atomic mass 39.948 (1) g/mol
                                     Electron configuration [Ne] 3s^2 3p^6
                                               Electrons per shell 2, 8, 8
                                                       Physical properties
                                           Phase gas (At room temperature)
                                              Density (0 °C, 101.325 kPa)
                                                                 1.784 g/L
                                                    Melting point 83.80  K
                                              (-189.35 ° C, -308.83 ° F)
                                                     Boiling point 87.30 K
                                              (-185.85 ° C, -302.53 ° F)
                                        Critical point 150.87 K, 4.898 MPa
                                          Heat of fusion 1.18 kJ·mol^−1
                                    Heat of vaporization 6.43 kJ·mol^−1
                         Heat capacity (25 °C) 20.786 J·mol^−1·K^−1

   CAPTION: Vapor pressure

                                             P/Pa  1 10 100 1 k 10 k 100 k
                                            at T/K   47 53  61   71   87

                                                         Atomic properties
                                     Crystal structure cubic face centered
                                                        Oxidation states 0
                                 Electronegativity no data (Pauling scale)
                                                       Ionization energies
                                          ( more) 1st: 1520.6 kJ·mol^−1
                                                  2nd: 2665.8 kJ·mol^−1
                                                    3rd: 3931 kJ·mol^−1
                                                       Atomic radius 71 pm
                                               Atomic radius (calc.) 71 pm
                                                     Covalent radius 97 pm
                                               Van der Waals radius 188 pm
                                                             Miscellaneous
                                             Magnetic ordering nonmagnetic
                     Thermal conductivity (300 K) 17.72 mW·m^−1·K^−1
                                      Speed of sound (gas, 27 °C) 323 m/s
                                             CAS registry number 7440-37-1
                                                         Selected isotopes

                  CAPTION: Main article: Isotopes of argon

                                iso    NA    half-life DM  DE ( MeV)  DP
                               ^36Ar 0.337%  Ar is stable with 18 neutrons
                               ^37Ar syn     35 d      ε    ?        ^37Cl
                               ^38Ar 0.063%  Ar is stable with 20 neutrons
                               ^39Ar syn     269 y     β^- 0.565     ^39K
                               ^40Ar 99.600% Ar is stable with 22 neutrons
                               ^42Ar syn     32.9 y    β^- 0.600     ^42K

                                                                References

   Argon ( IPA: /ˈɑːgɒn/) is a chemical element designated by the symbol
   Ar. Argon has atomic number 18 and is the third element in group 18 of
   the periodic table ( noble gases). Argon is present in the Earth's
   atmosphere at slightly less than 1%, making it the most common noble
   gas on Earth.

Characteristics

   Argon and oxygen have approximately the same solubility in water and
   are 2.5 times more soluble in water than nitrogen. This highly stable
   chemical element is colorless, odorless, tasteless and nontoxic in both
   its liquid and gaseous forms. Argon is inert under most conditions and
   forms no confirmed stable compounds at room temperature. The creation
   of argon hydrofluoride (HArF), a metastable compound of argon with
   fluorine and hydrogen, was first reported by researchers at the
   University of Helsinki in 2000.

   Although the neutral ground-state chemical compounds of argon are
   presently limited to HArF, argon can form clathrates with water when
   atoms of it are trapped in a lattice of the water molecules. Also
   argon-containing ions e.g. ArH+ and excited state complexes e.g. ArF
   are well known. Theoretical calculations on computers have shown
   several argon compounds that should be stable but for which no
   synthesis routes are currently known.

Applications

   Canisters containing Argon Gas for use in extinguishing fire without
   damaging server equipment
   Enlarge
   Canisters containing Argon Gas for use in extinguishing fire without
   damaging server equipment
   An argon and mercury discharge tube. The mercury vapour glows brightly
   when an electric current is passed through it while the argon acts as
   the current carrier.
   Enlarge
   An argon and mercury discharge tube. The mercury vapour glows brightly
   when an electric current is passed through it while the argon acts as
   the current carrier.

   Argon is used in incandescent lighting and other applications in which
   diatomic nitrogen is not sufficiently inert. Argon will not react with
   the filament of light bulbs even at high temperatures. Other uses:
     * Argon is used as an inert gas shield in many forms of welding,
       including metal inert gas welding and tungsten inert gas welding.
     * as the gas of choice for the plasma used in ICP spectroscopy.
     * as a non-reactive blanket in the manufacture of titanium and other
       reactive elements.
     * as a protective atmosphere for growing silicon and germanium
       crystals.
     * as a gas for use in plasma globes.
     * as a gas for thermal insulation in energy efficient windows.
     * Argon-39 has been used for a number of applications, primarily ice
       coring. It has also been used for ground water dating.
     * Cryosurgery procedures such as cryoablation use liquified argon to
       destroy cancer cells.
     * Liquid argon is used in calorimetry in experimental particle
       physics.
     * Argon is used in technical scuba diving to inflate the dry suit,
       because it is inert and has low thermal conductivity.
     * Blue argon lasers are used in surgery to weld arteries, destroy
       tumors, and to correct eye defects.
     * Due to its inert qualities, it is commonly used by museum
       conservators to protect old materials or documents, which are prone
       to gradual oxidation in the presence of air.
     * Argon is used to keep open bottles of wine from oxidizing, and is
       used in a number of dispensing units and keeper cap systems.
     * Argon is used in winemaking as barrels are often topped off with
       the gas to displace oxygen, thus preventing the wine from turning
       to vinegar during the aging process.
     * Argon is used in surgery when doctors are working in areas where it
       is easy for the person to die from blood loss and dries up all the
       bleeding as soon as the cut is opened by a sharp tool with a pipe
       connected to it which blows argon gas onto the inscision

History

   Argon ( Greek αργός meaning "inactive") was suspected to be present in
   air by Henry Cavendish in 1785 but was not discovered until 1894 by
   Lord Rayleigh and Sir William Ramsay in an experiment in which they
   removed all of the oxygen and nitrogen from the air. Argon was also
   encountered in 1882 through independent research of H.F. Newall and
   W.N. Hartley. Each observed new lines in the colour spectrum of air but
   were unable to identify the element responsible for the lines. Argon
   became the first member of the noble gases to be discovered.

   The symbol for Argon is now Ar, but until 1957 it was A.

Occurrence

   Argon constitutes 0.934% by volume and 1.29% by mass of the Earth's
   atmosphere, and air is the primary raw material used by industry to
   produce purified argon products. Argon is isolated from air by
   fractionation, most commonly by cryogenic fractional distillation, a
   process that also produces purified nitrogen, oxygen, neon, krypton and
   xenon.

   The Martian atmosphere in contrast contains 1.6% of argon-40 and 5 ppm
   of argon-36. The Mariner spaceprobe fly-by of the planet Mercury in
   1973 found that Mercury has a very thin atmosphere with 70% argon,
   believed to result from releases of the gas as a decay product from
   radioactive materials on the planet. In 2005, the Huygens probe also
   discovered the presence of argon-40 on Titan, the largest moon of
   Saturn.

Compounds

   Argon’s complete octet of electrons indicates full s and p subshells.
   This full outer energy level makes argon very stable and extremely
   resistant to bonding with other elements. Before 1962, argon and the
   other noble gases were considered to be chemically inert and unable to
   form compounds; however, compounds of the heavier noble gases have
   since been synthesized. In 2000, the first argon compounds were formed
   by researchers at the University of Helsinki. By shining ultraviolet
   light onto frozen argon containing a small amount of hydrogen fluoride,
   argon hydrofluoride (HArF) was formed. It is stable up to 40 kelvins
   (−233 ° C).

Isotopes

   The main isotopes of argon found on Earth are ^40Ar, ^36Ar, and ^38Ar.
   Naturally occurring ^40K with a half-life of 1.250×10^9 years, decays
   to stable ^40Ar (11.2%) by electron capture and by positron emission,
   and also transforms to stable ^40Ca (88.8%) via beta decay. These
   properties and ratios are used to determine the age of rocks.

   In the Earth's atmosphere, ^39Ar is made by cosmic ray activity,
   primarily with ^40Ar. In the subsurface environment, it is also
   produced through neutron capture by ^39K or alpha emission by calcium.
   ^37Ar is created from the decay of ^40Ca as a result of subsurface
   nuclear explosions. It has a half-life of 35 days.
   Retrieved from " http://en.wikipedia.org/wiki/Argon"
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   with only minor checks and changes (see www.wikipedia.org for details
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