Argon
Atomic Number: 18
Symbol: Ar
Atomic Weight: 39.948
Discovery: Sir William Ramsey, Baron Rayleigh, 1894 (Scotland)
Electron Configuration: [Ne] 3s2 3p6
Word Origin: Greek: argos: inactive
Isotopes: Eight isotopes of argon are known. Natural argon is a mixture of three stable isotopes. The other five isotopes are radioactive.
Properties: Argon has a freezing point of -189.2°C, boiling point of -185.7°C, and density of 1.7837 g/l. Argon is considered to be a noble or inert gas and does not form true chemical compounds, although it does form a hydrate with a dissociation pressure of 105 atm at 0°C. Ion molecules of argon have been observed, including (ArKr)+, (ArXe)+, and (NeAr)+. Argon forms a clathrate with b hydroquinone, which is stable yet without true chemical bonds. Argon is two and a half times more soluble in water than nitrogen, with approximately the same solubility as oxygen. Argon's emission spectrum includes a characteristic set of red lines.
Uses: Argon is used in electric lights and in fluorescent tubes, photo tubes, glow tubes, and in lasers. Argon is used as an inert gas for welding and cutting, blanketing reactive elements, and as a protective (nonreactive) atmosphere for growing crystals of silicon and germanium.
Sources: Argon gas is prepared by fractionating liquid air. The Earth's atmosphere contains 0.94% argon. Mars' atmosphere contains 1.6% Argon-40 and 5 ppm Argon-36.
Element Classification: Inert Gas
Density (g/cc): 1.40 (@ -186°C)
Melting Point (K): 83.8
Boiling Point (K): 87.3
Appearance: colorless, tasteless, odorless noble gas
Atomic Radius (pm): 2-
Atomic Volume (cc/mol): 24.2
Covalent Radius (pm): 98
Specific Heat (@20°C J/g mol): 0.138
Evaporation Heat (kJ/mol): 6.52
Debye Temperature (K): 85.00
Pauling Negativity Number: 0.0
First Ionizing Energy (kJ/mol): 1519.6
Lattice Structure: Face-Centered Cubic
Lattice Constant (Å): 5.260
References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952), CRC Handbook of Chemistry & Physics (18th Ed.), CRC Handbook of Chemistry & Physics (1983.)
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