Argon at Chemical Elements.com 

Basic Information


Name: Argon
Symbol: Ar
Atomic Number: 18
Atomic Mass: 39.948 amu
Melting Point: -189.3 °C (83.85 °K, -308.74 °F)
Boiling Point: -186.0 °C (87.15 °K, -302.8 °F)
Number of Protons/Electrons: 18
Number of Neutrons: 22
Classification: Noble Gas
Crystal Structure: Cubic
Density @ 293 K: 1.784 g/cm3
Color: Colorless Gas


Atomic Structure

[Bohr Model of Argon]  
Number of Energy Levels: 3

    First Energy Level: 2
    Second Energy Level: 8
    Third Energy Level: 8

Isotopes

Isotope Half Life
Ar-36 Stable
Ar-37 35.0 days
Ar-38 Stable
Ar-39 269.0 years
Ar-40 Stable
Ar-41 1.8 hours

Facts


Date of Discovery: 1894
Discoverer: Sir William Ramsey
Name Origin: From the Greek word argon (inactive)
Uses: Lighting
Obtained From: air