1 atom
×
16.000
(the atomic weight of oxygen)
16.000 amu
2 atoms ×
1.008 (the atomic weight of hydrogen)
2.016 amu
molecular weight of water
18.016 amu
hydrogen
2 atoms ×
1.008 amu
2.016 amu
sulfur
1 atom × 32.064 amu
32.064 amu
oxygen
4 atoms × 15.999 amu
63.996 amu
molecular weight
98.076 amu
hydrogen
1 atom ×
1.008 amu
1.008 amu
chlorine
1 atom × 35.453 amu
35.453 amu
molecular weight
36.461 amu
CHARACTERISTICS OF ATOMS
DOE-HDBK-1015/1-93
Fundamentals of Chemistry
CH-01
Rev. 0
Page 8
Example 1:
The compound water has a formula of HO. This means there is one atom of
2
oxygen and two atoms of hydrogen. Calculate the molecular weight.
Solution:
The molecular weight is calculated as follows:
Example 2:
Calculate the molecular weight of HSO .
2
4
Solution:
Example 3:
Calculate the molecular weight of HCl.
Solution:
Avogadro's Number
Consider one atom of oxygen and one atom of sulfur, and compare their atomic weights.
Oxygen's atomic weight = 15.999 amu
Sulfur's atomic weight = 32.06 amu
The sulfur atom weighs approximately twice as much as the oxygen atom.
(32.06 ÷ 15.99 2)
