[hee-lee-uh
m] 
| an inert, gaseous element present in the sun's atmosphere and in natural gas, and also occurring as a radioactive decomposition product, used as a substitute for flammable gases in dirigible balloons. Symbol: He; atomic weight: 4.0026; atomic number: 2; density: 0.1785 g/l at 0°C and 760 mm pressure. |
| colorless liquid helium existing below its boiling point of 4.2 K and above the lambda point of 2.186 K. |
| liquid helium existing as a superfluid below the lambda point of 2.186 K, having very low viscosity and very high thermal conductivity. |
| he·li·um (hē'lē-əm) n. Symbol He A colorless, odorless inert gaseous element occurring in natural gas and with radioactive ores. It is used as a component of artificial atmospheres and laser media, as a refrigerant, as a lifting gas for balloons, and as a superfluid in cryogenic research. Atomic number 2; atomic weight 4.0026; boiling point -268.9°C; density at 0°C 0.1785 gram per liter. See Table at element. [From Greek hēlios, sun (so called because its existence was deduced from the solar spectrum); see sāwel- in Indo-European roots.] |
A chemical element, usually found in the form of a gas, in which two electrons are in orbit, and the nucleus consists of two protons and two neutrons. Its symbol is He.
Note: Helium is the best known of the inert gases.
Note: Because it is lighter than air, helium is used to fill balloons.
helium he·li·um (hē'lē-əm)
n.
Symbol He
An inert gaseous element occurring in natural gas and used as a component of artificial atmospheres and laser media. Atomic number 2; atomic weight 4.0026; boiling point -268.9°C; density at 0°C 0.1785 gram per liter.
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