18Ar39.948
Argon
Noble gases · gas at STP · Block P
About
Argon is the third-most abundant gas in the Earth's atmosphere, making up nearly 1%. As a noble gas, it is colorless, odorless, and extremely inert. This non-reactive property makes it highly useful as a protective atmosphere in arc welding, electronics manufacturing to protect sensitive components, and as a fill gas in incandescent and fluorescent light bulbs to prevent filament oxidation.
Atomic Properties
Atomic Number18
Atomic Weight39.948 u
Neutrons (common)22
Electron Configuration[Ne] 3s² 3p⁶
Full Configuration1s² 2s² 2p⁶ 3s² 3p⁶
Electrons per Shell2, 8, 8
Electron Affinity-96 kJ/mol
Oxidation States0
Covalent Radius97 pm
Van der Waals Radius188 pm
Periodic Table Position
Group18
Period3
BlockP
Chemical SeriesNoble gases
Physical Properties
State at STPgas
Appearancecolorless gas
Crystal Structurefcc
Magnetic Orderingdiamagnetic
Speed of Sound323 m/s
Thermal Properties
Melting Point83.8 K
Boiling Point87.3 K
Triple Point83.806 K
Thermal Conductivity0.018 W/(m·K)
Specific Heat0.52 J/(g·K)
Molar Heat20.786 J/(mol·K)
Heat of Fusion1.18 kJ/mol
Heat of Vaporization6.53 kJ/mol
Abundance
In Earth's Crust3.5 ppm
In Ocean0.45 ppm
In Solar System102 ppm
In Universe200 ppm
Discovery
Discovered byLord Rayleigh & William Ramsay
Discovery Year1,894
Occurrenceprimordial
CAS Number7440-37-1
Electron Configuration
Energy
↿⇂
↿⇂
↿⇂
↿⇂
↿⇂
↿⇂
↿⇂
↿⇂
↿⇂
4s
3d
4p
5s
4d
5p
6s
4f
5d
6p
7s
5f
6d
7p
Isotopes of Argon
| Symbol ▲ | Mass (u) ▲ | Abundance ▲ | Half-life ▲ | Decay Mode ▲ |
|---|---|---|---|---|
| 36Ar | 35.967545 | 0.334% | Stable | Stable |
| 38Ar | 37.962732 | 0.063% | Stable | Stable |
| 39Ar | 38.964313 | Trace | 268 y | Beta Minus Decay |
| 40Ar | 39.962383 | 99.603% | Stable | Stable |
| 42Ar | 41.963046 | — | 32.9 y | Beta Minus Decay |
Interactive Visualization
Explore the 3D Bohr model of Argon in our interactive viewer.
View 3D Model of Argon