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A chemical
substance is a material with a specific chemical composition.
It is a concept that became firmly established in the late
eighteenth century after work by the chemist Joseph Proust on
the composition of some pure chemical compounds such as basic
copper carbonate. He deduced that, "All samples of a compound
have the same composition; that is, all samples have the same
proportions, by mass, of the elements present in the
compound." This is now known as the law of constant
composition. Later with the advancement of methods for
chemical synthesis particularly in the realm of organic
chemistry; the discovery of many more chemical elements and
new techniques in the realm of analytical chemistry used for
isolation and purification of elements and compounds from
chemicals that led to the establishment of modern chemistry,
the concept was defined as is found in most chemistry
textbooks. However, there are some controversies regarding
this definition mainly because the large number of chemical
substances reported in chemistry literature need to be
indexed.
A common example of a chemical substance is pure water; it has
the same properties and the same ratio of hydrogen to oxygen
whether it is isolated from a river or made in a laboratory. A
pure chemical substance cannot be separated into other
substances by a process that does not involve any chemical
reaction and is rarely found in nature. Some typical chemical
substances can be diamond, gold, salt (sodium chloride) and
sugar (sucrose). Generally, chemical substances exist as a
solid, liquid, or gas, and may change between these phases of
matter with changes in temperature or pressure.
Forms of energy, such as light and heat, are not considered to
be matter, and thus they are not "substances" in the
scientific regard. |
