"Atomic weight" is often loosely and incorrectly used as a synonym for standard atomic weight (incorrectly because standard atomic weights are not from a single sample). It is sometimes interpreted as the expected range of the relative atomic mass values for the atoms of a given element from all terrestrial sources, with the various sources being taken from Earth. The more common, and more specific quantity known as standard atomic weight ( A r, standard) is an application of the relative atomic mass values obtained from multiple different samples. For example, due to a different mixture of stable carbon-12 and carbon-13 isotopes, a sample of elemental carbon from volcanic methane will have a different relative atomic mass than one collected from plant or animal tissues. This quantity can vary substantially between samples because the sample's origin (and therefore its radioactive history or diffusion history) may have produced unique combinations of isotopic abundances. Since both quantities in the ratio are masses, the resulting value is dimensionless hence the value is said to be relative.įor a single given sample, the relative atomic mass of a given element is the weighted arithmetic mean of the masses of the individual atoms (including their isotopes) that are present in the sample. The atomic mass constant (symbol: m u) is defined as being 1 / 12 of the mass of a carbon-12 atom. Relative atomic mass (symbol: A r sometimes abbreviated RAM or r.a.m.), also known by the deprecated synonym atomic weight, is a dimensionless physical quantity defined as the ratio of the average mass of atoms of a chemical element in a given sample to the atomic mass constant.
0 Comments
Leave a Reply. |