The Atom
...elements may also combine into systems
called MOLECULES, which are the smallest units
of chemical COMPOUNDS. In all these ordinary
processes, atoms may be considered as the
ancient Greeks imagined them to be: the ultimate
building blocks of matter. When stronger forces
are applied to atoms, however, the atoms may
break up into smaller parts. Thus atoms are
actually composites and not units, and have a
complex inner structure of their own. By studying
the processes in which atoms break up, scientists
in the 20th century have come to understand many
details of the inner structure of atoms. The size of
a typical atom is only about 10 (-10th) meters. A
cubic centimeter of solid matter contains
something like 10 (24th) atoms. Atoms cannot be
seen using optical microscopes, because they are
much smaller than the wavelengths of visible light.
By using more advanced imaging techniques such
as electron microscopes, scanning tunneling
microscopes, and atomic force microscopes,
however, scientists have been able to produce
images in which the sites of individual atoms can
be identified. EARLY ATOMIC THEORIES The
first recorded speculations that MATTER
consisted of atoms are found in the works of the
Greek philosophers LEUCIPPUS and
DEMOCRITUS. The essence of their views is
that all phenomena are to be understood in terms
of the motions, through empty space, of a large
number of tiny and indivisible bodies. (The name
"atom" comes from the Greek words atomos, for
"indivisible.") According to Democritus, these
bodies differ from one another in shape and size,
and the observed variety of substances derives
from these differences in the atoms composing
them. Greek atomic theory was not an attempt to
account for specific details of physical phenomena.
It was instead a philosophical response to the
question of how change can occur in nature....
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