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metal

(Encyclopedia)metal, chemical element displaying certain properties by which it is normally distinguished from a nonmetal, notably its metallic luster, the capacity to lose electrons and form a positive ion, and th...

Bohr, Niels Henrik David

(Encyclopedia)Bohr, Niels Henrik David bōr [key], 1885–1962, Danish physicist, one of the foremost scientists of modern physics. He studied at the Univ. of Copenhagen (Ph.D. 1911) and carried on research on the...

catalyst

(Encyclopedia)catalyst, substance that can cause a change in the rate of a chemical reaction without itself being consumed in the reaction; the changing of the reaction rate by use of a catalyst is called catalysis...

airship

(Encyclopedia)airship, an aircraft that consists of a cigar-shaped gas bag, or envelope, filled with a lighter-than-air gas to provide lift, a propulsion system, a steering mechanism, and a gondola accommodating pa...

aurora borealis

(Encyclopedia)aurora borealis ôstrāˈlĭs [key], luminous display of various forms and colors seen in the night sky. The aurora borealis of the Northern Hemisphere is often called the northern lights, and the aur...

neutron

(Encyclopedia)neutron, uncharged elementary particle of slightly greater mass than the proton. It was discovered by James Chadwick in 1932. The stable isotopes of all elements except hydrogen and helium contain a n...

nitrate

(Encyclopedia)nitrate, chemical compound containing the nitrate (NO3) radical. Nitrates are salts or esters of nitric acid, HNO3, formed by replacing the hydrogen with a metal (e.g., sodium or potassium) or a radic...

mucopolysaccharide

(Encyclopedia)mucopolysaccharide myo͞oˌkəpŏlēsăkˈərīd [key], class of polysaccharide molecules, also known as glycosaminoglycans, composed of amino-sugars chemically linked into repeating units that give a...

technetium

(Encyclopedia)technetium tĕknēˈshēəm [key] [Gr. technetos=artificial], artificially produced radioactive chemical element; symbol Tc; at. no. 43; mass no. of most stable isotope 98; m.p. 2,200℃; b.p. 4,877�...

alkaloid

(Encyclopedia)alkaloid, any of a class of organic compounds composed of carbon, hydrogen, nitrogen, and usually oxygen that are often derived from plants. Although the name means alkalilike, some alkaloids do not e...