An atom is made up of a very small but heavy central nucleus with
a positive charge, surrounded by a negatively charged cloud of electrons.
Because atoms are so small, the familiar units of feet or centimeters
are useless in measuring them. A more common unit of length is the
angstrom, symbolized .
There are 100,000,000 or 10
in one centimeter, or to express matters the other way around,
1 = 1/10
cm = 10
cm = 0.00000001 cm
Most atoms are of the order of 1.0
in diameter, which is why angstroms are so convenient. The nucleus
of an atom is much smaller yet, typically with a diameter of 10
cm or 10
If an atom were as large as a football stadium, the nucleus would
be the size of a small ladybug crawling across the 50-yard line.
In spite of this size difference, virtually an of the mass of an
atom is concentrated in its nucleus. One electron, which has a negative
charge, weighs only 1/1836 as much as the lightest of all nuclei,
that of the hydrogen atom (proton).