Atomic weights

weight (wāt)

1. heaviness; the degree to which a body is drawn toward the earth by gravity. 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 a system of weights used in compounding prescriptions, based on the grain (64.8 mg). Its units are the scruple (20 grains), dram (3 scruples), ounce (8 drams), and pound (12 ounces).

atomic weight the sum of the masses of the constituents of an atom; it can be expressed in atomic mass units, SI units, or as a dimensionless ratio based on its value relative to the 12C isotope of carbon, defined as 12.00000. Abbreviated At wt.

avoirdupois weight the system of weight commonly used for ordinary commodities in English-speaking countries; its units are the grain, dram (27.344 grains), ounce (16 drams), and pound (16 ounces).

equivalent weight the amount of a substance that combines with or displaces 8.0 g of oxygen (or 1.008 g of hydrogen); it is the ratio of the molecular weight to the number of protons (acid/base reactions) or electrons (redox reactions) involved in the reaction.

molecular weight the weight of a molecule of a substance as compared with that of an atom of carbon-12; it is equal to the sum of the atomic weights of its constituent atoms and is dimensionless. Abbreviated Mol wt or MW. Although widely used, it is not technically correct; relative molecular mass (M r) is preferable.

atomic weight

n. Abbr. at wt, AW

The average mass of an atom of an element, usually expressed relative to the atomic mass of carbon 12.

atomic weight.

See atomic mass.

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.

atomic weight,

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

atomic (

tom´ik),

adj pertaining to the atom.

atomic energy,

n See energy, atomic.

atomic mass number,

n (symbol: A), the total number of nucleons (protons and neutrons) of which an atom is composed.

atomic number (Z),

n 1. the number of electrons outside the nucleus of a neutral atom.
n 2. the number of protons in the nucleus.

atomic structure theory,

n the theory that matter is composed of a vast number of particles, or atoms, bound together by a force of attraction of electrical charges.

atomic weight,

n the weight of one atom of an element as compared with the weight of an atom of hydrogen.

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.

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atomic weight (redirected from Atomic weights)

atomic weight
(redirected from Atomic weights)