Chemistry Reference
In-Depth Information
A preliminary term for the chemical elements already appeared in the philo-
sophic schools of ancient Greece: Empedocles talked about the four roots of all
things, which he perceived in a mythical way as deities. These four deities represent
earth, fire, air and water, out of which every being is made - the term “element” can
be traced back to him. Closer inspection of this idea reveals that the Greek
philosophers developed this and other constructs without any experiments: “Indeed
their achievements were based on a range of thorough and classified observation in
nature, but there can be no talk of experimentation in a scientific way.”
The alchemy of medieval times was dominated by the idea of producing gold
from base metal: small amounts of gold and silver were set free during the
refinement of ore. It was also tried to obtain gold and silver by “metal transmuta-
tion” in many ways. During those attempts it was observed that metallic copper
deposits, when to vitriol solution - nowadays called a copper sulfate solution - an
iron nail is placed. The alchemist van Helmont found that he could also obtain
copper from vitriol solution in different other ways and that “copper is somehow
contained in the vitriol solution” and just needed to be isolated. The way how
“copper is contained” could not be answered.
Boyle took up this thought in his work “The Skeptical Chymist,” to arrive at his
theory of elements being basic substances, which cannot be decomposed. He
pointed out repeatedly that theories about chemical substances cannot be consid-
ered valid, unless they are proven by experimental evidence.
However, Lavoisier was the first to successfully topple the phlogiston theory by
consequent usage of scales. He showed that pure metals are indecomposable, whereas
“metal limes” (today: metal oxides) deliver metal and colorless gases. With his
famous mercury oxide decomposition (see Fig. 1.1), he found that red mercury
oxide produces silvery shining liquid mercury and colorless gas which ignites a
glowing wooden splint. Because of his experiments with dissolved metal and non-
metal oxides in water and proving that nonmetal oxides show acidic reactions, he
called that colorless gas “oxygen” and defined the basics of the “oxidation theory.”
After many experiences concerning mercury and other pure metals Lavoisier
stated that these substances should be
elements
, and the decomposable substances
compounds
. But he also considered that at first indecomposable substances may be
later proven to be decomposable with improved technology: “Certain substances
are chemically considered to be elements, unless and as long as we do not have an
instrument to further decompose them. They are elements for us and our aspects,
pour nous, a` notre e´gard
”[
2
].
The preliminary ideas of the elements, the old Greek philosophy, the Phlogiston
theory, and others were the base for thinking and acting before the time of
Lavoisier. With the help of his decomposition hypothesis Lavoisier derived many
experiments and proved his hypothesis step by step - through him the experiment
got the scientific meaning of an instrument that judges the validity of assumptions,
principles, and theories!
According to the chemical elements, a big last step has to appear in science
history: the connection of the idea of elements with the idea of atoms as smallest
particles. Through his experiments Dalton found this relationship, defined the
