The periodic table is one of the great classifications
of the natural world and ranks on a par with several other major classifications,
including the classification of plant species by Linnaeus in the 1750s, the
classification of stars by Hertzsprung and Russell in 1913, and the
classification of subnuclear particles by Gell-Mann and Ne’eman in the 1950s.
The periodic table has for its primary purpose the
classification of the chemical elements, the basis for this being the analogies
they exhibit in their physical and chemical properties. As the story of the
periodic table is closely entwined with that of the elements, we shall explore
these two concepts concomitantly here. From this broad perspective, some of the
most colorful events that have occurred in chemical history over the past 2600
years are encompassed. In developing our theme, we shall endeavor to stimulate
a greater interest in and bring a new awareness of the very rich legacy
bequeathed to us by our pioneering predecessors. It is our hope that such an approach
may in some way compensate for the often rather cursory treatment afforded our
theme in elementary chemistry textbooks and foundational courses.
Because there can be no periodic table without an understanding
of the nature of the elements, we shall start by delving into the history of
the chemical elements. First, we mention the somewhat ironic fact that around
nine genuine elements were known in ancient times, these being carbon, sulfur,
copper, iron, lead, tin, mercury, silver, gold, and possibly antimony, though
none of them was recognized as an element. Like everything else that was
material, these true elements were thought to be composed of metaphysical
entities such as essences or principles. The notion that all material objects
consisted of essences or principles was a remarkably enduring one that was to
persist for well over 2000 years.
In fact, this notion remained dominant until the end
of the alchemical era was reached toward the end of the eighteenth century. In
the Western World, the conception of meta physical elements is usually traced
back to and considered to originate from certain of the natural philosophers of
ancient Greece.
However, it is important to point out that all of the
other major civilizations of the past paid homage to the idea that physical reality
manifests itself in terms of metaphysical entities that were regarded as
elements. There was even substantial overlap in these entities in different
civilizations. Thus, virtually all of the early civilizations conceived of air
and fire as elements.
Before probing further into the history of the
elements, a brief comment on the etymological derivation of the word element
seems appropriate. The first usage of the term element was made by the Greek
philosopher Plato (427–347 BCE) in the fifth century BCE. The Latin equivalent of
this Greek term is elementum, and this was first used by the Roman poet
Lucretius in his famous poem De Rerum Natura (On the Nature of Things)
extolling the virtues of an atomic conception of the world. While on the subject
of words, we mention in passing the origin of the word quintessence. It was
thought by the ancient Greeks that four elements comprised all of the matter on
Earth whereas the celestial sphere was constituted from only one transcendent element
referred to as the ether or the quinta essentia, the fifth essence, from which
our modern word quintessence is derived. Interestingly, the ether turned out to
be by far the longest lived of the Greek elements, for it was not until the dawn
of the twentieth century that belief in the ether was finally abandoned.
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