and the mass of one mole of any substance is its atomic or molecular mass (these
values are given in the Periodic Table of Elements). For example, the mass of a
carbon-12 atom (the most abundant isotope of carbon) has a mass of exactly 12
atomic mass units, and a mole of these atoms has a mass of 12 grams. Oxygen has
an atomic mass of 16 g, so a mole of carbon dioxide (CO 2 ), which is made up of
one carbon atom and two oxygen atoms, has a mass of 12 g + 2(16 g) = 44 g. The
molar mass of an object is defined as M = mNA, where m represents the unit mass
of a certain substance.
The Mole
The mole is a unit of measurement
that expresses
the quantity of a certain
substance. It has the unit
symbol mol and is related
to Avogadro’s constant,
NA = 6.022 × 10^23. For
example, a mol of oxygen
is 6.022 × 10^23 atoms of
oxygen.