| atomic weight | <chemistry> The average weight of an atom of an element, i.e. The total mass of protons and neutrons in an atom. (09 Oct 1997) |
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| gram-atomic weight | Atomic weight expressed in grams. Compare: mole. (05 Mar 2000) |
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| atomic | 1. Of or pertaining to atoms. 2. Extremely minute; tiny. Atomic philosophy, or Doctrine of atoms, a system which assuming that atoms are endued with gravity and motion accounted thus for the origin and formation of all things. This philosophy was first broached by Leucippus, was developed by Democritus, and afterward improved by Epicurus, and hence is sometimes denominated the Epicurean philosophy. <chemistry> Atomic theory, or the Doctrine of definite proportions, the weight of the atom of an element as compared with the weight of the atom of hydrogen, taken as a standard. Origin: Cf. F. Atomique. Source: Websters Dictionary (01 Mar 1998) |
| atomic absorption spectrophotometry | Determination of concentration by the ability of atoms to absorb radiant energy of specific wavelengths. (05 Mar 2000) |
| atomic bomb | <physics, radiobiology> A weapon with a large explosive power due to the sudden release of energy when the nuclei of heavy atoms such as plutonium-239 or uranium-235 are split. This fission is brought about by the bombardment of the fuel with neutrons, setting off a chain reaction. The bomb releases shock, blast, heat, light, and lethal radiation. The world's first atomic bomb was successfully tested by the United States on July 16, 1945. (13 Nov 1997) |
| atomic core | The nucleus plus the nonvalence electrons. (05 Mar 2000) |
| atomic heat | The amount of heat required to raise an atom from 0 |
| atomic mass | <chemistry, physics> The mass of an atom relative to other atoms. The present-day basis of the scale of atomic weights is carbon, the most common isotope of this element has arbitrarily been assigned an atomic weight of 12. The unit of the scale is 1/12 the weight of the carbon atom or roughly the mass of one proton or one neutron. The atomic weight of any element is approximately equal to the total number of protons and neutrons in is nucleus (16 Dec 1997) |
| atomic mass unit | <chemistry> One-twelfth the mass of a neutral atom of the most abundant isotope of carbon. (16 Dec 1997) |
| atomic number | <chemistry> Symbol Z. The number of protons in the nucleus of an atom and also its characteristic atomic number. The atomic numbers of the known elements form a complete series from 1 (hydrogen) to 103 (lawrencium). (16 Dec 1997) |
| atomic theory | That chemical compounds are formed by the union of atoms in certain definite proportions; in its modern form, first advanced in 1803 by John Dalton. (05 Mar 2000) |
| atomic volume | The atomic weight of an element divided by its density in the solid state; the volume of the gram-atomic weight of a solid element. (05 Mar 2000) |
| microscopy, atomic force | Microscopy in which a probe systematically rides across the surface of a sample being scanned in a raster pattern. The vertical position is recorded as a spring attached to the probe rises and falls in response to peaks and valleys on the surface. A microcomputer keeps track of the vertical excursions as a function of the position of the probe in the horizontal plane and presents the sample's image. (12 Dec 1998) |
| spectrophotometry, atomic absorption | A highly sensitive technique used to analyze various elements, especially metals, including aluminum, arsenic, beryllium, calcium, copper, iron, lead, and lithium, which are present in trace amounts. The atoms are excited above a ground state by flame vaporization, and the radiation emitted as the molecules return to a ground state is measured in unexcited non-ionised molecules. (12 Dec 1998) |
| adrenal weight factor | A postulated substance of adenohypophysial origin responsible for maintenance of the weight of the adrenal cortex. (05 Mar 2000) |
| apothecaries' weight | An obsolescent system of weights based upon the weight of a grain of wheat. Has been used for centuries in weighing medicines and precious metals (Troy measure). Some drugs which have been available for long periods are still often designated as grains (e.g., 5 grains of aspirin, 1/2 grain of codeine, 1/100 grain nitroglycerin). This weight system has been largely superseded by the metric system (based on grams). One grain is the equivalent of 64.8 milligrams. One scruple contains 20 grains; one dram contains 60 grains; one apothecary ounce contains 8 drams (480 grains); one apothecary pound contains 12 ounces (5760 grains). (05 Mar 2000) |