atomic weight

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weight

 [wāt]
1. heaviness; the degree to which a body is drawn toward the earth by gravity. (See also Tables of Weights and Measures in the Appendix.) Abbreviated wt.
2. in statistics, the process of assigning greater importance to some observations than to others, or a mathematical factor used to apply such a process.
apothecaries' weight see apothecaries' system.
atomic weight the sum of the masses of the constituents of an atom, expressed in atomic mass units (or daltons), in SI units (i.e., kilograms), or as a dimensionless ratio derived by comparing the mass to the mass of an atom of carbon-12, which is taken as 12.000. Abbreviated At wt.
avoirdupois weight see avoirdupois system.
equivalent weight the amount of substance that combines with or displaces 8.0 g of oxygen (or 1.008 g of hydrogen), usually expressed in grams; for acid/base reactions, one equivalent donates or receives a mole of protons and the equivalent weight is the ratio of the molecular weight to the number of protons involved in the reaction. For oxidation-reduction reactions, one equivalent donates or receives a mole of electrons and the equivalent weight is the ratio of the molecular weight to the number of electrons involved in the reaction.
gram molecular weight the molecular weight of a substance expressed in grams; one gram molecular weight of a molecular substance contains one mole of molecules. See also mole1.
low birth weight (LBW) see under infant.
molecular weight the weight of a molecule of a chemical compound as compared with the weight of an atom of carbon-12; it is equal to the sum of the weights of its constituent atoms and is dimensionless. Abbreviated Mol wt or MW. Although widely used, the term is not technically correct; relative molecular mass is preferable.
very low birth weight (VLBW) see under infant.

a·tom·ic weight (at. wt., AW),

the mass in grams of 1 mol (6.02 × 1023 atoms) of an atomic species; the mass of an atom of a chemical element in relation to the mass of an atom of carbon-12 (12C), which is set equal to 12.000, thus a ratio and therefore dimensionless (although the actual mass, numerically the same, is sometimes expressed in daltons); not necessarily the weight of any individual atom of an element, since most elements are made up of several isotopes of different masses; for example, the atomic weight of chlorine is 35.4527, because it is composed of 35Cl and 37Cl in proportions that give an average of 35.4527.
See also: molecular weight.

atomic weight

a·tom·ic weight

(AW, at. wt.) (ă-tom'ik wāt)
The mass in grams of 1 mol (6.02 × 1023, atoms) of an atomic species; the mass of an atom of a chemical element in relation to the mass of an atom of carbon 12 (12C), which is set equal to 12.000, thus a ratio and therefore dimensionless (although the actual mass, numerically the same, is sometimes expressed in daltons); not necessarily the weight of any individual atom of an element, because most elements are made up of several isotopes of different masses.
See also: molecular weight

atomic weight

the weight of an atom of an element in relation to hydrogen, which is considered as one.

atomic weight,

n the total number of protons and neutrons within an atom's nucleus. This number represents the atom's approximate mass.

a·tom·ic weight

(AW, at. wt.) (ă-tom'ik wāt)
The mass in grams of 1 mol (6.02 × 1023, atoms) of an atomic species.
See also: molecular weight

weight

heaviness; the degree to which a body is drawn toward the earth by gravity. See also Tables 4.1 and 4.2.

apothecaries' weight
an outmoded system of weight used in compounding prescriptions based on the grain (equivalent 64.8 mg). Its units are the scruple (20 grains), dram (3 scruples), ounce (8 drams) and pound (12 ounces). See also Tables 4.2 and 4.3.
atomic weight
the weight of an atom of a chemical element, compared with the weight of an atom of carbon-12, which is taken as 12.00000.
avoirdupois weight
the system of weight still used for ordinary commodities in some English-speaking countries. Its units are the dram (27.344 grains), ounce (16 drams) and pound (16 ounces).
birth weight
weight of the newborn at the time of birth.
body weight
the animal's weight. In herbivores this is often debatable because of the variation in 'gut-fill' depending on the availability of palatable food. In the absence of scales the weights of large animals are often estimated on the basis of their age and their girth just behind the elbow. Called also liveweight. See also body condition score.
body weight-to-surface area
determination of many drug dosages is physiologically more accurate when based on body surface area rather than body weight; used particularly in cancer chemotherapy. For conversion table for use in dogs see Table 21.
equivalent weight
the weight in grams of a substance that is equivalent in a chemical reaction to 1.008 g of hydrogen. See also chemical equivalent.
weight gain
increase in body weight for specific periods; the principal measure of productivity in meat animals.
weight loss
the loss of body weight from that previously measured. This estimate must take into account the difference in 'gut-fill' and the effects of developing pregnancy and recent parturition.
metric weight
see Tables 4.1 and 4.2.
molecular weight
the weight of a molecule of a chemical compound as compared with the weight of an atom of carbon-12; it is equal to the sum of the weights of its constituent atoms. Abbreviated mol. wt. See also Table 6.
shifting weight limb to limb
sign indicative of lameness especially in horses; while standing the horse is continually shifting its weight from one limb to the opposite one of the pair.
References in periodicals archive ?
The standard atomic weights, including the proton and electron reference masses were taken from the web-site of the National Institute of Standards (NIST) and were expressed in the atomic mass unit u.
Now that it has completed the initial round, the International Union of Pure and Applied Chemistry's commission in charge of atomic weights will reassess the rest of the elements in the coming years.
Following approval by the International Union of Pure and Applied Physics and the International Union of Pure and Applied Chemistry, atomic weights are based on the carbon-12 nucleus equals 12 scale.
Berzelius published his table of atomic weights in 1826 with quite a few that were not an integral multiple of that of hydrogen.
Consequently some atomic weights ought to be reported as ranges, rather than the deceivingly exact numbers commonly printed on periodic tables.
Reuters reports that a team of German scientists discovered a new element with "an atomic weight of 272 - meaning it is 272 times heavier than hydrogen.
It was then found that the vast majority of atomic weights of the polynuclidic elements could be reproduced through continued fractions as well.
Isotopes are variants of the same element with different atomic weights.
Isotopes are variants of the same chemical element with different atomic weights due to having different numbers of neutrons, such as the most common carbon isotope, carbon-12, and a heavier stable isotope, carbon-13.
This results in those rare earths with lower atomic numbers and atomic weights actually having larger atoms than elements that are higher in the periodic table.
Table gets flex The atomic weights of 10 chemical elements in the periodic table (including chlorine, below) are listed as ranges rather than single numbers, the first phase in an overhaul of almost every element in the table (SN: 1/29/11, p.
Russian chemist Dmitri Mendeleev gets the credit for arranging the elements according to their atomic weights.