[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.
| helium (hē'lē-əm) Pronunciation Key
Symbol He A very lightweight, colorless, odorless element in the noble gas group. Helium occurs in natural gas, in radioactive ores, and in small amounts in the atmosphere. It has the lowest boiling point of any substance and is the second most abundant element in the universe. Helium is used to provide lift for balloons and blimps and to create artificial air that will not react chemically. Atomic number 2; atomic weight 4.0026; boiling point -268.9°C; density at 0°C 0.1785 gram per liter. See Periodic Table. Our Living Language : The second most abundant element in the universe after hydrogen, Helium (symbol He) is a colorless, odorless, nonmetallic gas that is produced abundantly by the nuclear fusion in all stars and is found in smaller amounts on Earth. It was discovered by the British scientist—and founding editor of the journal Nature—Joseph Norman Lockyer in 1868, while he was studying a solar eclipse with a spectroscope, an instrument that breaks light up into a spectrum. If an element is heated up enough to glow, the emitted light produces a unique spectrum when refracted through a prism. Lockyer noticed that the spectrum of the Sun's corona, which is visible only during a solar eclipse, contained lines produced by an unknown element. He named the element helium from helios, the Greek word for "sun." Helios gives us many other words pertaining to the Sun, such as heliocentric and perihelion. |
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