Fundamentals of Chemistry
Forming Chemical Compounds
Chemistry and all other sciences are based on facts established through experimentation. A
scientific law is a condensed statement of facts which has been discovered by experiment.
There are three basic laws that apply to chemical reactions. They are the Law of Conservation
of Mass, the Law of Definite Proportions, and the Law of Multiple Proportions. These laws
are described here to help the reader in understanding the reasons elements and compounds
behave as they do.
The Law of Conservation of Mass
This law states that in a chemical reaction the total mass of the products equals
the total mass of the reactants. Antoine Lavoisier, a French chemist, discovered
that when tin reacts with air in a closed vessel, the weight of the vessel and its
contents is the same after the reaction as it was before. Scientists later
discovered that whenever energy (heat, light, radiation) is liberated during a
reaction, a very small change in mass does occur, but this change is insignificant
in ordinary chemical reactions.
The Law of Definite Proportions
This law states that no matter how a given chemical compound is prepared, it
always contains the same elements in the same proportions by mass. John
Dalton, an English physicist, discovered that when various metals are burned or
oxidized in air, they always combine in definite proportions by weight.
For example, one part by weight of oxygen always combines with 1.52 parts by
weight of magnesium or 37.1 parts by weight of tin. This law results from the
fact that a compound is formed by the combination of a definite number of
atoms of one element with a definite number of atoms of another.
The Law of Multiple Proportions
This law states that if two elements combine to form more than one compound,
the masses of one of the elements combining with a fixed mass of the other are
in a simple ratio to one another. For example, carbon forms two common
compounds with oxygen; carbon monoxide and carbon dioxide. With carbon
monoxide (CO), 1.33 grams of oxygen are combined with 1 gram of carbon.
With carbon dioxide (CO ), 2.67 grams of oxygen are combined with 1 gram of
carbon. Therefore, the masses of oxygen combining with a fixed mass of carbon
are in the ratio 2:1.