- Notes: The spectroscopic data below are for the isotope 4 He. He I Ground State 1s 2 1 S 0 Ionization energy 198310.669 cm-1 (24.587387 eV) Ref. M02 He II Ground State 1s 2 S 1 / 2.
- Hydrogen is a chemical element with atomic number 1 which means there are 1 protons and 1 electrons in the atomic structure. The chemical symbol for Hydrogen is H. With a standard atomic weight of circa 1.008, hydrogen is the lightest element on the periodic table. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass.
Helium Mass Number 3
Chemical, Physical and Thermal Properties of Helium - He
Chemical, physical and thermal properties of Helium - He :
(values at 25oC (77oF, 298 K) and atmospheric pressure)
The two gases have comparable mass (H 2 and He). Single helium atoms are so small they pass between many other molecules. This is why a filled helium balloon deflates over time - the helium escapes through tiny pores in the material. Atomic number 2 is the second most abundant element in the universe, after hydrogen.
| Molecular Weight | 4.0026 |
| Specific Gravity, air = 1 | 0.138 |
| Specific Volume (ft3/lb, m3/kg) | 97.86, 6.11 |
| Density of liquid at atmospheric pressure (lb/ft3, kg/m3) | 7.80, 125 |
| Absolute Viscosity (lbm/ft s, centipoises) | 13.4 10-6, 0.02 |
| Sound velocity in gas (m/s) | 1015 |
| Specific Heat - cp - (Btu/lboF or cal/goC, J/kgK) | 1.24, 5188 |
| Specific Heat Ratio - cp/cv | 1.66 |
| Gas constant - R - (ft lb/lboR, J/kgoC) | 386, 2077 |
| Thermal Conductivity (Btu/hr ft oF, W/moC) | 0.086, 0.149 |
| Boiling Point - saturation pressure 14.7 psia and 760 mm Hg - (oF, oK) | -452, 4.22 |
| Latent Heat of Evaporation at boiling point (Btu/lb, J/kg) | 10.0, 23300 |
| Critical Temperature (oF, oK) | -450.3, 5.2 |
| Critical Pressure (psia, MN/m2) | 33.22, - |
| Critical Volume (ft3/lb, m3/kg) | 0.231, 0.0144 |
| Flammable | no |
Follow the links below to get values for the listed properties of helium at varying pressure and temperature:
See also more about atmospheric pressure, and STP - Standard Temperature and Pressure & NTP - Normal Temperature and Pressure,
as well as Thermophysical properties of: Acetone, Acetylene, Air, Ammonia, Argon, Benzene, Butane, Carbon dioxide, Carbon monoxide, Ethane, Ethanol, Ethylene, Hydrogen, Hydrogen sulfide, Methane, Methanol, Nitrogen, Oxygen, Pentane, Propane, Toluene, Water and Heavy water, D2O.
Related Topics
Helium Mass Number
- Material Properties - Material properties for gases, fluids and solids - densities, specific heats, viscosities and more
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