Atomic Number: 18
Atomic Weight: 39.948
Discovery: Sir William Ramsay, Baron Rayleigh, 1894 (Scotland)
Electron Configuration: [Ne] 3s2 3p6
Word Origin: Greek: argos: inactive
Isotopes: There are 22 known isotopes of argon ranging from Ar-31 to Ar-51 and Ar-53. Natural argon is a mixture of three stable isotopes: Ar-36 (0.34%), Ar-38 (0.06%), Ar-40 (99.6%). Ar-39 (half-life = 269 yrs) is to determine the age of ice cores, ground water and igneous rocks.
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
CAS Registry Number: 7440–37–1
- The first noble gas to be discovered was argon.
- Argon glows violet in a gas discharge tube.
- William Ramsay, in addition to argon, discovered all the noble gases except radon. This earned him the 1904 Noble Prize in Chemistry.
- The original atomic symbol for argon was A. In 1957, the IUPAC changed the symbol to the current Ar.
- Argon is the 3rd most common gas in Earth's atmosphere.
- Argon is produced commercially by fractional distillation of air.
- Substances are stored in argon gas to prevent interactions with the atmosphere.
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.) International Atomic Energy Agency ENSDF database (Oct 2010)