helium

• POS: Noun
• HYPHEN: he=li=um

CIDE DICTIONARY

helium, n. [NL., fr. Gr. "h`lios the sun.].

 An inert, monoatomic, gaseous element occurring in the atmosphere of the sun and stars, and in small quantities in the earth's atmosphere, in several minerals and in certain mineral waters. It is obtained from natural gas in industrial quantities. Symbol, He; atomic number 2; at. wt., 4.0026 (C=12.011). Helium was first detected spectroscopically in the sun by Lockyer in 1868; it was first prepared by Ramsay in 1895. Helium has a density of 1.98 compared with hydrogen, and is more difficult to liquefy than the latter. Chemically, it is an inert noble gas, belonging to the argon group, and cannot be made to form compounds. The helium nucleus is the charged particle which constitutes alpha rays, and helium is therefore formed as a decomposition product of certain radioactive substances such as radium. The normal helium nucleus has two protons and two neutrons, but an isotope with only one neutron is also observed in atmospheric helium at an abundance of 0.013 %. Liquid helium has a boiling point of -268.9Webster 1913 Suppl.]

OXFORD DICTIONARY

helium, n. Chem. a colourless light inert gaseous element occurring in deposits of natural gas, used in airships and as a refrigerant.

Usage

Symb.: He.

Etymology

Gk helios sun (having been first identified in the sun's atmosphere)