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alkyl group

(Encyclopedia)alkyl group ălˈkĭl [key], in chemistry, group of carbon and hydrogen atoms derived from an alkane molecule by removing one hydrogen atom (see radical). The name of the alkyl group is derived from t...

fallout

(Encyclopedia)fallout, minute particles of radioactive material produced by nuclear explosions (see atomic bomb; hydrogen bomb; Chernobyl) or by discharge from nuclear-power or atomic installations and scattered th...

biodiesel

(Encyclopedia)biodiesel, fuel made from natural, renewable sources, such as new and used vegetable oils and animal fats, for use in a diesel engine. Biodiesel has physical properties very similar to petroleum-deriv...

gunpowder

(Encyclopedia)gunpowder, explosive mixture; its most common formula, called “black powder,” is a combination of saltpeter, sulfur, and carbon in the form of charcoal. Historically, the relative amounts of the c...

Franklin, Rosalind Elsie

(Encyclopedia)Franklin, Rosalind Elsie, 1920–58, English molecular biologist and chemist, grad. Newnham College, Cambridge (1941). She spent most of the war years (1942–45) working for the British Coal Utilisat...

chemical bond

(Encyclopedia)chemical bond, mechanism whereby atoms combine to form molecules. There is a chemical bond between two atoms or groups of atoms when the forces acting between them are strong enough to lead to the for...

protactinium

(Encyclopedia)protactinium prōˌtăktĭnˈēəm [key], radioactive chemical element; symbol Pa; at. no. 91; mass number of most stable isotope 231; m.p. greater than 1,600℃; b.p. 4,026℃; sp. gr. 15.37 (calcula...

quartz

(Encyclopedia)quartz, one of the commonest of all rock-forming minerals and one of the most important constituents of the earth's crust. Chemically, it is silicon dioxide, SiO2. It occurs in crystals of the hexagon...

occupational disease

(Encyclopedia)occupational disease, illness incurred because of the conditions or environment of employment. Unlike with accidents, some time usually elapses between exposure to the cause and development of symptom...

energy, sources of

(Encyclopedia)energy, sources of, origins of the power used for transportation, for heat and light in dwelling and working areas, and for the manufacture of goods of all kinds, among other applications. The develop...