The Foundations of Chemistry

As Table 2-4 suggests, the concept of a mole as applied to atoms is especially useful.
It provides a convenient basis for comparing the masses of equal numbers of atoms of
different elements.
Figure 2-9 shows what one mole of atoms of each of some common elements looks
like. Each of the examples in Figure 2-9 represents 6.022
1023 atomsof the element.
The relationship between the mass of a sample of an element and the number of moles
of atoms in the sample is illustrated in Example 2-3.
In this textbook we usually work problems involving atomic weights (masses) or for-
mula weights (masses) rounded to only one decimal place. We round the answer further
if initial data do not support the number of significant figures obtained using the rounded
atomic weights. Similarly, if the initial data indicate that more significant figures are jus-
tified, we will rework such problems using atomic weights and formula weights contain-
ing values beyond the tenths place.

Figure 2-8 Three ways of representing amounts.

2-6 The Mole 59

12 large eggs

or

1 dozen eggs

or

24 ounces of eggs

6.022 
 1023 Fe atoms

or

1 mole of Fe atoms

or

55.847 grams of iron

TABLE 2-4 Mass of One Mole of Atoms of Some Common

Elements

A Sample with a

Element Mass of Contains

carbon 12.0 g C 6.02
 1023 C atoms or 1 mol of C atoms

titanium 47.9 g Ti 6.02
 1023 Ti atoms or 1 mol of Ti atoms

gold 197.0 g Au 6.02
 1023 Au atoms or 1 mol of Au atoms

hydrogen 1.0 g H 2 6.02
 1023 H atoms or 1 mol of H atoms

(3.01
 1023 H 2 molecules or ^12 mol

of H 2 molecules)

sulfur 32.1 g S 8 6.02
 1023 S atoms or 1 mol of S atoms

(0.753
 1023 S 8 molecules or ^18 mol

of S 8 molecules)