APPENDIX 1
General Chemical
Relationships
ATOMIC AND MOLECULAR WEIGHTS
VALENCE
Atomic and molecular weights are basic to all quantitative chemical reactions and
are used in all calculations associated with these reactions. An understanding of the
principles of their use is necessary to apply them to the calculations involved in
chemical determinations. The molecular weight of H 2 S0 4 and percentage composition
ofthe elements in this compound may be obtained by referring to the atomic weights as
follows:
Hydrogen, 2 at wt = 2 x 1.008 = 2.016
Sulfur, 1 at wt = 1 x 32.060 = 32.060
Oxygen, 4 at wt = 4 x 16.000 = 64.000
Molecular wt 98.076
The percentage by weight of hydrogen is 2.016/98.076 x 100 = 2.056. A complete listing
of atomic weights and numbers and other elemental parameters can be found in various
handbooks.
In all cases, knowing the equation for a given reaction, the weight ratios can be
determined from the atomic weights of the elements and the formulas of the
compounds involved. Because the weight ratios can be calculated, when the actual
weight of any compound entering into the reaction is known, the weights of all of the
other compounds involved can also be determined.
The combining power, or ratio in which atoms of one element combine with atoms of
other elements, is called valence. The valence of hydrogen is 1; the valence of the other
elements is determined by their electron charge and is evaluated by examining the
formula of the compound in which the element occurs. The positive and negative
valences of elements in different compounds assume different values under various
conditions, but the sum of positive and negative valences for anyone compound must
be equal to O.
359
General Chemical
Relationships
ATOMIC AND MOLECULAR WEIGHTS
VALENCE
Atomic and molecular weights are basic to all quantitative chemical reactions and
are used in all calculations associated with these reactions. An understanding of the
principles of their use is necessary to apply them to the calculations involved in
chemical determinations. The molecular weight of H 2 S0 4 and percentage composition
ofthe elements in this compound may be obtained by referring to the atomic weights as
follows:
Hydrogen, 2 at wt = 2 x 1.008 = 2.016
Sulfur, 1 at wt = 1 x 32.060 = 32.060
Oxygen, 4 at wt = 4 x 16.000 = 64.000
Molecular wt 98.076
The percentage by weight of hydrogen is 2.016/98.076 x 100 = 2.056. A complete listing
of atomic weights and numbers and other elemental parameters can be found in various
handbooks.
In all cases, knowing the equation for a given reaction, the weight ratios can be
determined from the atomic weights of the elements and the formulas of the
compounds involved. Because the weight ratios can be calculated, when the actual
weight of any compound entering into the reaction is known, the weights of all of the
other compounds involved can also be determined.
The combining power, or ratio in which atoms of one element combine with atoms of
other elements, is called valence. The valence of hydrogen is 1; the valence of the other
elements is determined by their electron charge and is evaluated by examining the
formula of the compound in which the element occurs. The positive and negative
valences of elements in different compounds assume different values under various
conditions, but the sum of positive and negative valences for anyone compound must
be equal to O.
359