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 People realized
that atoms
exists surely.
Then they questioned
what the size
of an atom is.
According to various
experiments,
Avogadro's constant
has turned out to be
Since a solid
like a metal block
is tightly filled
with atoms as shown
in the following figure,
we can easily estimate
the size of the atom.
Suppose the radius of atom
to be r cm.
Then
atoms would line up in 1 cm
and
atoms occupy
the volume of
Suppose the density
of the metal to be
Let the molecular
weight of the metal,
which is equal to
the atomic weight
in the case of metal,
be A.
The volume of
1 mol
of the metal
is
 .
Therefore the volume
occupied by one atom
of the metal
is obtained by dividing
by Avogadro's constant
NA.
Namely,
Accordingly, the radius
of the atom is
considered to be
For example,
the radii of some
solid-state atoms
estimated by using
the above formula
are listed in the following
Table.
From these results,
we can presume that
the size of
an atom is approximately
several angstroms
(1 angstrom
= 10-8 cm
= 10-10 m).
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