Hydrogen: physical properties
Under ambient conditions, hydrogen is a colourless highly flammable diatomic gas with the molecular formula H2. Hydrogen gas has no small or taste. It is possible to make liquid hydrogen at atmospheric pressure by cooling it to below 20.28 K (-252.87 °C). Liquid hydrogen can be stored in insulated containers under pressure. Solid hydrogen may be made by cooling below the melting point of 14.01 K (-259.14 °C) and has a low density 88 kg m-3 (0.088 g cm-3). Hydrogen is not an electrical conductor. It may be that a liquid metallic hydrogen is present in the highly compressed interiors of Jupiter and Saturn where pressures are in the millions of atmospheres.
Mechanical properties
Density properties
Density of solid: 88 kg m‑3
Molar volume: 11.42 cm3
Elastic properties
Young's modulus: (no data) GPa
Rigidity modulus: (no data) GPa
Bulk modulus: (no data) GPa
Poisson's ratio: (no data) (no units)
Hardnesses
Mineral hardness: (no data) (no units)
Brinell hardness: (no data) MN m-2
Vickers hardness: (no data) MN m-2
Electrical properties
Electrical resistivity: (no data) × 10‑8 Ω m; or mΩ cm
Heat and conduction
Thermal conductivity: 0.1805 W m‑1 K‑1
Coefficient of linear thermal expansion: (no data) × 10‑6 K‑1
Optical properties
Reflectivity: (no data) %
Refractive index: 1.000132 (gas; liquid 1.12) (no units)
Acoustic properties
Velocity of sound: 1270 m s‑1
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