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- It is an average of relative isotope masses for an element from samples collected all over the Earth, so this value is subject to change as new element sources are discovered.
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Jul 1, 2019 · The atomic weight can change because it depends on our understanding of how much of each isotope of an element exists. Both atomic mass and atomic weight rely on the atomic mass unit (amu), which is 1/12th the mass of an atom of carbon-12 in its ground state.
- Anne Marie Helmenstine, Ph.D.
The atomic mass (relative isotopic mass) of an uncommon isotope can differ from the relative atomic mass, atomic weight, or standard atomic weight, by several mass units. Relative isotopic masses are always close to whole-number values, but never (except in the case of carbon-12) exactly a whole number, for two reasons:
The relative masses of atoms are reported using the atomic mass unit (amu), which is defined as one-twelfth of the mass of one atom of carbon-12, with 6 protons, 6 neutrons, and 6 electrons. The atomic mass of an element is the weighted average of the masses of the naturally occurring isotopes.
Atomic mass is a property unique to each element, while atomic weight is a value that can vary depending on the abundance of isotopes. Atomic mass is used to calculate the molar mass of a substance, while atomic weight is used to determine the amount of a substance in a chemical reaction.
Feb 25, 2021 · Atomic mass is calculated by measuring the masses of protons, neutrons, and electrons of the atom. Atomic weight is calculated by determining the percentage abundance of all the isotopes of a chemical element. Atomic mass doesn’t depend on the isotopic mass of different isotopes of an element.
Atomic weight can be defined as the average weight of an element with respect to all its isotopes and their relative abundances. Atomic weight is measured in units of atomic mass (usually abbreviated to AMU), also known as Daltons. A single element can have several isotopes.
The preference for the term ‘atomic mass’ over ‘atomic weight’ in scientific discourse stems from the desire for accuracy and clarity. Here’s why atomic mass is considered more correct: 1. Consistency with Fundamental Definitions. Mass is a fundamental property of matter, while weight is a force.
