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The molecular mass (for molecular compounds) and formula mass (for non-molecular compounds, such as ionic salts) are commonly used as synonyms of molar mass, differing only in units (daltons vs g/mol); however, the most authoritative sources define it differently. The difference is that molecular mass is the mass of one specific particle or ...
The IUPAC definition [1] of relative atomic mass is: An atomic weight (relative atomic mass) of an element from a specified source is the ratio of the average mass per atom of the element to 1/12 of the mass of an atom of 12 C.
The molar mass is usually the more appropriate quantity when dealing with macroscopic (weigh-able) quantities of a substance. The definition of molecular weight is most authoritatively synonymous with relative molecular mass; however, in common practice, use of this terminology is highly variable. When the molecular weight is given with the ...
Thus, the atomic mass of a carbon-12 atom is 12 Da by definition, but the relative isotopic mass of a carbon-12 atom is simply 12. The sum of relative isotopic masses of all atoms in a molecule is the relative molecular mass. The atomic mass of an isotope and the relative isotopic mass refers to a certain specific isotope of an element.
It can be converted into a measure of mass (with dimension M) by multiplying it with the dalton, also known as the atomic mass constant. Among various variants of the notion of atomic weight (A r, also known as relative atomic mass) used by scientists, the standard atomic weight (A r °) is the most common and practical.
The molar mass constant, usually denoted by M u, is a physical constant defined as one twelfth of the molar mass of carbon-12: M u = M(12 C)/12. [1] The molar mass of an element or compound is its relative atomic mass (atomic weight) or relative molecular mass (molecular weight or formula weight) multiplied by the molar mass constant.
Theoretical chemistry requires quantities from core physics, such as time, volume, temperature, and pressure.But the highly quantitative nature of physical chemistry, in a more specialized way than core physics, uses molar amounts of substance rather than simply counting numbers; this leads to the specialized definitions in this article.
The mass of an atom or other particle can be compared more precisely and more conveniently to that of another atom, and thus scientists developed the dalton (also known as the unified atomic mass unit). By definition, 1 Da (one dalton) is exactly one-twelfth of the mass of a carbon-12 atom, and thus, a carbon-12 atom has a mass of exactly 12 Da.