1. Elements and Compounds
Careful experimentation by Lavoisier and others led to the realization that
some pure substances were obviously chemical combinations of other pure
substances, while other substances were in some way fundamental and could
not be decomposed. The concept of fundamental substances from which all
other matter was composed had been introduced by Greek philosophers in
ancient times. They called these fundamental substances elements and
based their philosophy on the existence of four of them: earth, air, fire, and
water. Experiments from the early seventeenth century revealed flaws in this
philosophy, and alternative sets of elements were suggested, mercury, salt,
and sulfur for example, but as more observations were made it became
increasingly difficult to reconcile the facts with a small set of elements.
The boundaries of the transformation of chemistry from alchemical philosophy
to experimental science are marked by the publication of two important
books. The Sceptical Chymist, written by Robert Boyle and published in
1661, points out the problems with existing philosophies and argues that the
true nature of the elements should be discovered by experimentation. By
1789 the world was ready for the publication of the first modern chemistry
textbook, Traité Élémentaire de Chimie, written by Lavoisier and published in
English translation the following year as Elements of Chemistry. In his book
Lavoisier defined an element as a substance that could not be decomposed
by experiment into two or more other substances, and listed as elements 31
simple substances, most of which we still classify as elements.