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Unformatted text preview: 2.011 g
1 mol of O = 6.02214 * 1023 O atoms = 15.9994 g, and so on. ▲ Most elements are composed of mixtures of two or more isotopes so that the
atoms in a sample of the element are not all of the same mass but are present in
their naturally occurring proportions. Thus, in one mole of carbon, most of the
atoms are carbon-12, but some are carbon-13. In one mole of oxygen, most of
the atoms are oxygen-16, but some are oxygen-17 and some are oxygen-18. As
a result, The weighted-average
atomic mass of carbon was
calculated on page 48.
KEEP IN MIND
that molar mass has the unit
g> mol. FIGURE 2-17 One mole of an element
The watch glasses contain one mole of copper atoms (left)
and one mole of sulfur atoms (right). The beaker contains
one mole of mercury atoms as liquid mercury, and the
balloon, of which only a small portion is visible here,
contains one mole of helium atoms in the gaseous state. *Atomic mass (atomic weight) values in tables are often written without units, especially if they
are referred to as relative atomic masses. This simply means that the values listed are in relation
to exactly 12 (rather than 12 u) for carbon-12. We will use the atomic mass unit (u) when referring
to atomic masses (atomic weights). Most chemists do....
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