Argon (Ar)

Noble gases · Period 3 · Gas

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Element identity

Atomic number (Z): 18
Symbol: Ar
Atomic weight / isotope mass number: 39.95(16)
Category: Noble gases
Physical state (reference): Gas
Period: 3
Group (reference): 18
Block: p

Physical properties

Appearance: Colorless gas exhibiting a lilac/violet glow when placed in a high voltage electric field
Density: 1.784×10⁻³ g·cm⁻³
Melting point: 83.81 K / −189.34 °C / −308.81 °F
Boiling point: 87.302 K / −185.848 °C / −302.526 °F
Sublimation point: Not available

Atomic and material properties

Electron configuration: [Ne] 3s² 3p⁶
Electrons per shell: K2 L8 M8
Oxidation states: 0
Electronegativity (Pauling): Not available
Atomic radius: 71 pm
Covalent radius: 106±10 pm
Molar ionization energies: 1st: 1520.6 kJ·mol⁻¹ 2nd: 2665.8 kJ·mol⁻¹ 3rd: 3931 kJ·mol⁻¹ 4th: 5771 kJ·mol⁻¹ 5th: 7238 kJ·mol⁻¹ 6th: 8781 kJ·mol⁻¹ 7th: 11,995 kJ·mol⁻¹ 8th: 13,842 kJ·mol⁻¹ 9th: 40,760 kJ·mol⁻¹ 10th: 46,186 kJ·mol⁻¹ 11th: 52,002 kJ·mol⁻¹ 12th: 59,653 kJ·mol⁻¹ 13th: 66,199 kJ·mol⁻¹ 14th: 72,918 kJ·mol⁻¹ 15th: 82,473 kJ·mol⁻¹ 16th: 88,576 kJ·mol⁻¹ 17th: 397,605 kJ·mol⁻¹ 18th: 427,066 kJ·mol⁻¹
Thermal conductivity: 17.72×10⁻³ W·m⁻¹·K⁻¹
Molar heat capacity: 20.85 J·mol⁻¹·K⁻¹
Crystal structure: Face-centered cubic
CAS number: 7440-37-1

Property source: Wikipedia — Argon, adapted from the Nuclides App snapshot. Quoted conditions and qualifiers are retained.

Sources and interpretation

Snapshot exported 24 October 2026 from the element assets used by Nuclides. Properties are a reference compilation, not a new evaluation. Missing values are shown as “Not available”. Density and phase depend on temperature, pressure and allotrope; retained conditions are part of the quoted property.

Atomic weight is dimensionless. Parentheses give uncertainty in the last quoted digits. A single integer in square brackets is an isotope mass number, not a standard atomic weight. The snapshot can differ from current evaluations; consult CIAAW standard atomic weights and the IUPAC periodic table for current values and conventions.

Element properties in the App snapshot are adapted from Wikipedia. Each element page links to its source article; text adaptations are available under CC BY-SA 4.0. No third-party images are included.

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