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 ?
Another student from one of the high schools in Thimphu, Yangchen Dolkar, who also signed the petition, said the atomic weight table should have been provided as it had been in the past exams.
Atomic weights confirm bipolar model of oscillations in a chain system.
This was to develop into his success in correlating chemical properties and atomic weights in the periodic table.
If hydrogen was supposed to have an atomic weight of 1, oxygen would have one of 8.
5 does not apply at all to the relative atomic weights, while the bipolar model with phase shifts of approximately [+ or -] 1.
These adjustments may seem trivial, but they reflect a valuable recognition of the importance of atomic weight in chemistry--and reveal some of the nuances hiding within Feynman's concise sentence.
Entering the 19th century and the era of atomic weights and atomic theory, chemistry began to disengage from its qualitative and descriptive character in the previous century when applications of chemistry to medicine were directed to the understanding of disease rather than to its relief.
It is necessary to note that the dates published in the table of "Experience of Systems of Elements Founded on Their Atomic Weights and Chemical Similarity" permits us to use them in order to prove the correctness of Mendeleev's work.
Now, it's undergoing one of its most substantial changes in a decade with changes to the atomic weights of no fewer than 10 elements.
Just as the weight listed on your driver's license doesn't necessarily reflect your actual poundage, the official atomic weights of most chemical elements are actually more like ballpark estimates than precise constants.
Taylor, The Atomic Weights of the Elements, Review 2000, Pure Appl.
Since Dalton had first advanced his atomic theory (see 1803), chemists had been determining the atomic weights of the chemical elements.