Argon

18
Ar
Group
18
Period
3
Block
p
Protons
Electrons
Neutrons
18
18
22
General Properties
Atomic Number
18
Atomic Weight
39.948
Mass Number
40
Category
Noble gases
Color
Colorless
Radioactive
No
From the Greek argos, inactive
Crystal Structure
Face Centered Cubic
History
Argon was suspected to be present in air by Henry Cavendish in 1785.

It was not isolated until 1894 by Lord Rayleigh and Sir William Ramsay in Scotland.

Argon became the first member of the noble gases to be discovered.

In 1957, IUPAC agreed that the symbol should change from A to Ar.
Electrons per shell
2, 8, 8
Electron Configuration
[Ne] 3s2 3p6
Ar
Argon makes a distinctive blue-green gas laser
Physical Properties
Phase
Gas
Density
0.0017837 g/cm3
Melting Point
83.8 K | -189.35 °C | -308.83 °F
Boiling Point
87.3 K | -185.85 °C | -302.53 °F
Heat of Fusion
1.18 kJ/mol
Heat of Vaporization
6.5 kJ/mol
Specific Heat Capacity
0.52 J/g·K
Abundance in Earth's crust
0.00015%
Abundance in Universe
0.02%
Vial
Image Credits: Images-of-elements
Vial of glowing ultrapure argon
CAS Number
7440-37-1
PubChem CID Number
23968
Atomic Properties
Atomic Radius
71 pm
Covalent Radius
106 pm
Electronegativity
-
Ionization Potential
15.7596 eV
Atomic Volume
22.4 cm3/mol
Thermal Conductivity
0.0001772 W/cm·K
Oxidation States
0
Applications
Argon gas is used to fill conventional incandescent and fluorescent light bulbs.

Argon is also used as an inert gas shield for arc welding and cutting, as blanket for the production of titanium and other reactive elements.

It is used as a protective atmosphere for growing silicon and germanium crystals.
Argon is considered to be non-toxic
Isotopes
Stable Isotopes
36Ar, 38Ar, 40Ar
Unstable Isotopes
30Ar, 31Ar, 32Ar, 33Ar, 34Ar, 35Ar, 37Ar, 39Ar, 41Ar, 42Ar, 43Ar, 44Ar, 45Ar, 46Ar, 47Ar, 48Ar, 49Ar, 50Ar, 51Ar, 52Ar, 53Ar