Well, there are indeed lots subatomic particles, and new ones keep
being found, and we do not know if there may be more. Some are more
"elmentary" than others, in that some are the building blocks for the
others. Just as protons, neutrons and electrons are the building blocks
of atoms, there is a small list of ingredients for the large number of
particles we know of.
The list of ingredients are:
Quarks: There are six kinds, whimsically called "flavors" by
physicists, with whimsical names, up, down, strange, charm, top and
bottom. Of these, the up and down type quarks are the most important
for everyday particles, as they compose the neutrons and protons. A
proton has two up-flavored quarks and one down-flavored one, while a
neutron has two down-flavored ones and one up-flavored one. Mixing and
matching these types gives different particles. For exmple, three
up-type quarks stuck together makes a particle called a Delta++, which
a charge of +2. It's unstable and decays right away into a proton and a
charged pion. Each quark has an antimatter counterpart. An up quark and
an antidown quark make up a charged pion, called a pi+. The proton,
neutron, Delta++ and pions are known to be "composite", that is, made
up of quarks.
Gluons: These "stick" the quarks together. They are a lot like photons, except they interact with quarks (and other gluons).
Photons: You may already know about these -- light is made up of photons.
Leptons: A category name for electrons, and particles like
electrons. Heavier cousins of the electron are the muon (found in
cosmic rays) and the tau. As far as we can tell, they don't have pieces
making them up.
Neutrinos: Very light, neutral particles produced in some kinds of
nuclear interactions. A neutron will decay into a proton and an
electron and an electron antineutrino. There are three flavors, one
corresponding to each lepton (electron neutrino, muon neutrino, and tau
W and Z bosons -- carriers of the weak nuclear force, which has a
very short range. The W weighs about 80 times that of a proton and the
Z about 90 times that of a proton.
Apart from the quarks and gluons, the other particles don't really
stick to each other well enough to make composite particles.
Stuck-together combinations of quarks and gluons make up a large count
of the 293 particles your teacher mentioned, and new ones keep being
discovered. We can usually fit them into our models, saying "oh yeah,
that's just this and that kind of quark stuck together with gluons".
293 may be a little out of date by now. There are also "excited states"
where the quarks are found in orbits with more energy than other
states, and these are counted as additional particles.
You can find out all about particles and their interactions here at the Particle Data Group's web page
. Check out the "Particle Adventure" for fun, educational links.
(republished on 07/21/06)