Properties of Helium (He)
Helium is a chemical element with the symbol (He) and the atomic number 2. It is a colorless, odorless, tasteless, and non-toxic gas that is the second lightest and second most abundant element in the universe, primarily produced through nuclear fusion in stars.
The following table provides a comprehensive list of helium properties in both SI and US customary/Imperial units at normal temperature and pressure (NTP).
Click on the icon to switch between Metric and Imperial units.
| Physical Properties | Metric |
|---|---|
| Molar Mass | 4.0026 g/mol |
| Density (0°C) | 0.1786 kg/m3 |
| Dynamic Viscosity (25°C) | 19.9 µPa·s |
| Speed of Sound in Gas (0°C) | 973 m/s |
| Thermal Properties | Metric |
| Melting Point | -272.2 °C |
| Boiling Point | -268.9 °C |
| Thermal Conductivity (25°C) | 0.148 W/m·K |
| Specific Heat Capacity (Cp) | 5194 J/kg·K |
| Critical Constants | Metric |
| Critical Temperature (Tc) | -267.95 °C |
| Critical Pressure (Pc) | 0.23 MPa |
| Critical Density (ρc) | 69.3 kg/m3 |
| Electrical Properties | Metric |
| Relative Permittivity (εr) | 1.000684 |
| Optical Properties | Metric |
| Refractive Index (589 nm) | 1.000036 |
Unless stated otherwise, all values are taken at room temperature (approximately 20°C or 68°F) and 1 atm pressure. (1 atm = 101,325 Pa)
Related Pages
References: 1) Cardarelli, François. Materials Handbook: A Concise Desktop Reference. Switzerland: Springer International Publishing, 2018. 2) CRC Handbook of Chemistry and Physics, 97th Edition. United Kingdom: CRC Press, 2016-2017. 3) Yaws, Carl L. The Yaws Handbook of Physical Properties for Hydrocarbons and Chemicals. Netherlands: Elsevier Science, 2015. 4) Fire Protection Guide to Hazardous Materials, 14th Edition. United States: National Fire Protection Association, 2010.