Five important subatomic particles

For most beginning science students, the five most important subatomic
particles are the proton, neutron, electron, neutrino, and positron.
Each of these particles can be described completely by its mass, electric
charge, and spin. Because the mass of subatomic particles is so small, it
is usually not measured in ounces or grams but in atomic mass units (label:
amu) or electron volts (label: eV). An atomic mass unit is approximately
equal to the mass of a proton or neutron. An electron volt is actually
a unit of energy but can be used to measure mass because of the
relationship between mass and energy (E mc2).
All subatomic particles (indeed, all particles) can have one of three
electric charges: positive, negative, or none (neutral). All subatomic particles
also have a property known as spin, meaning that they rotate on
their axes in much the same way that planets such as Earth do. In general,
the spin of a subatomic particle can be clockwise or counterclockwise,
although the details of particle spin can become quite complex.
Proton. The proton is a positively charged subatomic particle with an
atomic mass of about 1 amu. Protons are one of the fundamental constituents
of all atoms. Along with neutrons, they are found in a very concentrated
region of space within atoms referred to as the nucleus.
The number of protons determines the chemical identity of an atom.
This property is so important that it is given a special name: the atomic
number. Each element in the periodic table has a unique number of protons
in its nucleus and, hence, a unique atomic number.
Neutron. A neutron has a mass of about 1 amu and no electric charge.
It is found in the nuclei of atoms along with protons. The neutron is nor-
mally a stable particle in that it can remain unchanged within the nucleus
for an infinite period of time. Under some circumstances, however, a neutron
can undergo spontaneous decay, breaking apart into a proton and an
electron. When not contained with an atomic nucleus, the half-life for this
change—the time required for half of any sample of neutrons to undergo
decay—is about 11 minutes.
The nuclei of all atoms with the exception of the hydrogen-1 isotope
contain neutrons. The nuclei of atoms of any one element may contain
different numbers of neutrons. For example, the element carbon is
made of at least three different kinds of atoms. The nuclei of all three
kinds of atoms contain six protons. But some nuclei contain six neutrons,
others contain seven neutrons, and still others contain eight neutrons.
These forms of an element that contain the same number of protons but
different numbers of neutrons are known as isotopes of the element.
Electron. Electrons are particles carrying a single unit of negative electricity
with a mass of about 1/1800 amu, or 0.0055 amu. All atoms contain
one or more electrons located in the space outside the atomic nucleus.
Electrons are arranged in specific regions of the atom known as energy
levels. Each energy level in an atom may contain some maximum number
of electrons, ranging from a minimum of two to a maximum of eight.
Electrons are leptons. Unlike protons and neutrons, they are not
thought to consist of any smaller particles but are regarded themselves as
elementary particles that cannot be broken down into anything simpler.
All electrical phenomena are caused by the existence or absence of
electrons or by their movement through a material.
Neutrino. Neutrinos are elusive subatomic particles that are created by
some of the most basic physical processes of the universe, like decay of
radioactive elements and fusion reactions that power the Sun. They were
originally hypothesized in 1930 by Swiss physicist Wolfgang Pauli
(1900–1958). Pauli was trying to find a way to explain the apparent loss
of energy that occurs during certain nuclear reactions.
Neutrinos (“little neutrons”) proved very difficult to actually find in
nature, however. They have no electrical charge and possibly no mass. They
rarely interact with other matter. They can penetrate nearly any form of matter
by sliding through the spaces between atoms. Because of these properties,
neutrinos escaped detection for 25 years after Pauli’s prediction.