Argon

Argon (Ar)

Monatomic noble gas. Makes up 0.93% of the air. Colourless, odorless. Is inert and has no true compounds. Lord Rayleigh and Sir william Ramsey identified argon in 1894.
Atomic Number18
Atomic Weight39.948
Mass Number40
Group18
Period3
Blockp
Protons18 p+
Neutrons22 n0
Electrons18 e-
Argon ice 1.jpg Animated Bohr Model Enhanced Bohr Model Bohr Model Orbital Diagram

Properties

Atomic Radius
71 pm
Atomic Volume
Covalent Radius
96 pm
Metallic Radius
Ionic Radius
Crystal Radius
Van der Waals radius
188 pm
Density
0.001633 g/cm³
Boiling Point
87.3 K
Melting Point
83.8 K
Electrons per shell2, 8, 8
Electronegativity
Electrophilicity
0.083201331459 eV/particle
Proton Affinity
369.2 kJ/mol
Electron Affinity
Ionization Potential
15.7596112 eV/particle
Heat of Vaporization
6.52 kJ/mol
Heat of Fusion
Heat of Formation
Molar Heat Capacity
20.786 J/(mol K)
Specific Heat Capacity
Thermal Conductivity
0.0177 W/(m K)
Gas Basicity
346.3 kJ/mol
Dipole Polarizability
11.083 a₀
C6 Dispersion Coefficient
64.2 a₀
Oxidation States0
Color
Colorless
Crystal StructureFace Centered Cubic (FCC)
Lattice Constant
5.26 Å
Bulk Modulus
Electrical Resistivity
Electron Configuration[Ne] 3s2 3p6
Magnetic Ordering
Magnetic Susceptibility
PhaseGas
Poisson Ratio
Shear Modulus
Young's Modulus
Allotropes
Alternate Names
Adiabatic Index
Appearance
Electric Conductivity
Critical Pressure
Critical Temperature
Curie Point
Electrical
Hardness
Magnetic Susceptibility
Magnetic
Neel Point
Neutron Cross Section
Neutron Mass Absorption
Gas Phase
Quantum Numbers
Refractive Index
Space Group
Speed of Sound
Superconducting Point
Thermal Expansion
Valence Electrons
Classification
CategoryNoble gases, Noble gases
CAS GroupVIII
IUPAC GroupVIIIA
Glawe Number3
Mendeleev Number114
Pettifor Number3
Geochemical Classvolatile
Goldschmidt Classatmophile
Radioactivity
RadioactiveNo
Decay Mode
Half-Life
Lifetime
Abundance
Abundance in Earth's crust
3.5 mg/kg
Abundance in Oceans
0.45 mg/L
Abundance in Human Body
Abundance in Meteor
Abundance in Sun
Abundance in Universe0.02%

Isotopes of Argon

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

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. From the Greek argos, inactive

DiscoverersSir William Ramsey, Baron Rayleigh
Discovery LocationScotland
Discovery Year1894
Name OriginGreek: argos (inactive).
Argon is considered to be non-toxic
Argon makes a distinctive blue-green gas laser

Uses

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. Used in lighting products. It is often used in filling incandescent light bulbs. Some is mixed with krypton in fluorescent lamps. Crystals in the semiconductor industry are grown in argon atmospheres.

Sources

Continuously released into the air by decay of radioactive potassium-40. Pure form is obtained from fractional distillation of liquid air.