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Atoms are composed of three basic particles: protons, neu-
trons and electrons. Electrons are extremely light, nega-
tively charged particles that exist as a cloud around the
center, or nucleus, of the atom. Sometimes the electrons
are said to occupy orbits around the nucleus. These elec-
trons are attracted to the nucleus because of the positively
charged protons that, along with the neutrons, make up the
nucleus. Atoms bond together in molecules when one atom
gives up or shares an electron with another atom. Chemical
reactions utilize this bonding process.
In all atoms, the number of electrons (and therefore the
number of negative charges) equals the number of protons
(positive charges). The number of protons or electrons in
an atom determines the chemical nature of the atom, and
each element has its own unique number (example: hydro-
gen = 1, helium - 2 etc.). The number of neutrons, how-
ever, may not always be the same in every atom of a par-
ticular element. Atoms of an element with different numbers
of neutrons are called isotopes. Every atom of a particular
element has the same atomic number, but different iso-
topes of a given element have different atomic weights.
It is the variable number of neutrons in the nucleus of an
atom that leads to a process called nuclear decay that
causes radiation. When an atom has too many or too few
neutrons in its nucleus, it will have a tendency to rearrange
itself spontaneously into a new combination of particles that
are more stable. In this decay process, bundles of excess
energy are shot out of the nucleus in one of a number of
ways.
When the neutrons are excessive, a neutron can
convert itself to a proton and shoot out an electron
at very high speed, known as beta radiation.
A proton may be converted to a neutron to cause
an unusual particle called a positron to be ejected
from the nucleus.
In still another process, the nucleus, in a vain
atempt to stabilize itself, kicks out two protons and
two neutrons all together as one particle, called an
alpha particle.
