Atomic Mass

What is the difference between atomic weight and atomic mass and molar mass and molecular weight?

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2014-09-26 17:08:07

The atomic mass is the mass of an atom at rest. This

refers to one atom, and is typically measured in so-called atomic

mass units, and describes a single isotope of that element. The

atomic weight is the abundance-weighted average mass of an

element (an average mass of all the isotopes that exist for that

element, weighted by how abundant each isotope is in nature).

Atomic weight is commonly reported in atomic mass units, as well as

in grams per mole. The molar mass is the mass of one mole of

something, and can refer to both a single element as well as

molecules and other compounds. The molecular weight is

essentially the same thing as the molar mass except that, as the

name implies, it refers to molecules rather than just elements. The

molar mass and molecular weight is typically given in units of

grams per mole.

The molecular weight of a compound is found by adding the atomic

weights of all of the atoms in the compound. Water, for example,

has a molecular weight of 18.0152 grams/mole, as there are two

hydrogen atoms that each have an atomic weight of 1.00079 g/mole

and one oxygen atom with an atomic weight 15.9994 grams/mole.

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