Instead, atomic mass is expressed in unified atomic mass units (unit symbol: u). A unit of mass that describes the mass of an atom or molecule. In chemistry, an atomic mass unit or AMU is a physical constant equal to one-twelfth of the mass of an unbound atom of carbon-12.It is a unit of mass used to express atomic masses and molecular masses.When the mass is expressed in AMU, it roughly reflects the sum of the number of protons and neutrons in the atomic nucleus (electrons have so much less mass … However, because each atom has a very small mass, this is not very helpful. amu A unit of mass equal to 1/12 the mass of the most abundant isotope of carbon, carbon-12, which is assigned a mass of 12. It is equal to the sum of the atomic masses of all the atoms present in one molecule of the substance.e.g. one molecule of water (H 2 O) contains two atoms of hydrogen and one atom of oxygen. The carbon-12 atom has six neutrons and six protons in its nucleus. Atomic mass can be expressed in grams. An atomic unit of mass is defined as accurately 1/12 the mass of a carbon-12 atom. 1 AMU = Average of the proton rest mass and the neutron rest mass. The atomic unit mass is symbolized as AMU or amu. n. Abbr. Number of protons in an atom. Atomic mass unit definition, a unit of mass, equal to 1/12 (0.0833) the mass of the carbon-12 atom and used to express the mass of atomic and subatomic particles. (a) One atomic mass unit is defined as exactly one-twelfth the mass of an atom of carbon-12. 1 atomic mass unit is defined as 1/12 of the mass of a single carbon-12 atom. atomic number. The atomic mass (m a or m) is the mass of an atom.Although the SI unit of mass is kilogram (symbol: kg), the atomic mass is often expressed in the non-SI unit dalton (symbol: Da, or u) where 1 dalton is defined as 1 ⁄ 12 of the mass of a single carbon-12 atom, at rest. 1 AMU = 1.67377 x 10 -27 kilogram or 1.67377 x 10 -24 gram. (d) Relative Formula Mass :- Its symbol is 'u'. atomic mass unit. See more. The molecular mass of substance is the relative mass of its molecule expressed in atomic mass unit(u). Define atomic mass unit. :18 1 u has a value of 1.660 539 066 60(50) × 10 −27 kg. Since 1961 the standard unit of atomic mass has been one-twelfth the mass of an atom of the isotope carbon-12.An isotope is one of two or more species of atoms of the same chemical element that have different atomic mass numbers (protons + … atomic mass unit synonyms, atomic mass unit pronunciation, atomic mass unit translation, English dictionary definition of atomic mass unit. Atomic weight, also called relative atomic mass, ratio of the average mass of a chemical element’s atoms to some standard. (b) The atomic mass of an element is the relative mass of its atom as compared with the mass of a carbon-12 atom taken as 12 units. (c) It means that one atom of oxygen is 16 times heavier than 1/12 of a C-12 atom. Molecular mass of NH3= Atomic mass of N + 3 x Atomic mass of H = 14 + 3 x 1 Q12 : Calculate the formula unit masses of ZnO, Na2O, K2CO3, given atomic masses of Zn = 65 u, Na = 23 u, K = 39 u, C = 12 u, and O = 16 u. atomic mass. The protons and neutrons of the nucleus account for nearly all of the total mass of atoms, with the electrons … isotopes. neutrons. Atomic mass unit definition is - a unit of mass for expressing masses of atoms, molecules, or nuclear particles equal to 1/12 the mass of a single atom of the most abundant carbon isotope 12C —called also dalton. the particles of the nucleus that have no charge. The average mass of all the isotopes of an element. Mass and the neutron rest mass of define atomic mass unit topper is 16 times heavier than 1/12 of a C-12 atom 539... Not very helpful rest mass one atomic mass unit or molecule than 1/12 of a carbon-12.... A value of 1.660 539 066 60 ( 50 ) × 10 −27 kg however, because atom. 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