Argon (Ar)

Stable isotopes of argon available from ISOFLEX

Isotope Z(p) N(n) Atomic Mass Natural Abundance Enrichment Level Physical Form
Ar-36 18 18 35.9675462 0.34% ≥99.90% Gas
Ar-38 18 20 37.9627322 0.06% 99.90% Gas
Ar-40 18 22 39.96238312 99.60% 99.99% Gas

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Argon was discovered in 1894 by Sir William Ramsay and Lord Rayleigh. Its name derives from the Greek word argos, meaning “inactive.”  Today the chemical symbol for argon is Ar, but until 1957 its symbol was simply A.

Argon is a colorless and odorless gas that is present to a very small extent in the atmosphere. It is practically insoluble in water. It makes a good atmosphere for working with air-sensitive materials since it is heavier than air and less reactive than N2. It is an effective “blanket” for the production of titanium and other reactive elements. It provides a protective atmosphere for growing silicon and germanium crystals.

Commercial applications for argon include its use in electric light bulbs and in fluorescent tubes. It is also used as an inert gas shield for arc welding and cutting. 

Properties of Argon

Name Argon
Symbol Ar
Atomic number 18
Atomic weight 39.948
Standard state Gas at 298 ºK
CAS Registry ID 7440-37-1 
Group in periodic table 18 
Group name Noble gas 
Period in periodic table
Block in periodic table p-block 
Color Colorless
Classification Nonmetallic 
Melting point -189.3 ºC
Boiling point -185.8 ºC
Thermal conductivity 0.01772  W/(m-K)
Heat of vaporization 6.5  kJ·mol-1
Heat of fusion 1.18  kJ·mol-1
Density 1.784 g/cm3
Electron configuration [Ne]3s23p6
Oxidation state 0

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