Chemical & Physical Properties of Argon
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.
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.