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The dalton or unified atomic mass unit (symbols: Da or u, respectively) is a unit of mass defined as 1 / 12 of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest. [1] [2] It is a non-SI unit accepted for use with SI.
Relation to SI units atomic mass unit, unified: u; AMU Same as dalton (see below) ≈ 1.660 539 068 92 (52) × 10 −27 kg [20] atomic unit of mass, electron rest mass: m e: ≈ 9.109 383 7139 (28) × 10 −31 kg [21] bag : ≡ 60 kg = 60 kg bag (Portland cement) ≡ 94 lb av = 42.637 682 78 kg: barge: ≡ 22 + 1 ⁄ 2 short ton = 20 ...
The atomic mass of atoms, ions, or atomic nuclei is slightly less than the sum of the masses of their constituent protons, neutrons, and electrons, due to (per E = mc 2). Atomic mass is often measured in dalton (Da) or unified atomic mass unit (u). One dalton is equal to 1 ⁄ 12 the mass of a carbon-12 atom in its natural state.
The unified atomic mass unit (symbol: u) is equivalent to the dalton. One dalton is approximately the mass of one a single proton or neutron. [2] The unified atomic mass unit has a value of 1.660 538 921 (73) × 10 −27 kg. [3] The amu without the "unified" prefix is an obsolete unit based on oxygen, which was replaced in 1961.
The molar mass of atoms of an element is given by the relative atomic mass of the element multiplied by the molar mass constant, M u ≈ 1.000 000 × 10 −3 kg/mol ≈ 1 g/mol. For normal samples from Earth with typical isotope composition, the atomic weight can be approximated by the standard atomic weight [2] or the conventional atomic weight.
This value is then used to calculate a new approximation to A r (e), and the process repeated until the values no longer vary (given the relative uncertainty of the measurement, 2.1 × 10 −9): this happens by the fourth cycle of iterations for these results, giving A r (e) = 5.485 799 111 (12) × 10 −4 for these data.
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.
"Atomic mass unit" is rarely used in the scientific literature. It is, however, used in some contexts such as some primary schools. "dalton" and "Da" is the prevailing and most common name and symbol for this unit. "unified atomic mass unit" (not to be confused with "atomic mass unit") with its symbol "u" is less commonly used but accepted by SI.