by Harry Stevens

Created on: February 18, 2009

The elementary particles are the particles that make up everything that we know and understand about our world and our universe. The majority of the particles that we know of are described by a wonderful masterpiece called the Standard Model. This model describes all of the known forces (except gravity) and particles (except the theoretical graviton). While the Standard Model is not entirely perfect in describing the way that the particles behave, it has, in its own way, an excellent method of grouping the particles to make it easier to understand their behaviors with other particles in the immediate vicinity.

The Standard Model divides all the particles in the universe into to categories: the fermions and the bosons. Fermions are the particles that have a 1/2 angular momentum (like 1/2, 3/2, 5/2, etc.). The bosons are the particles that have angular momentums that are integers (like 1, 2, 3, etc.). The fermions are further split into two major categories: the leptons and the quarks. Leptons are fundamental particles, and they include the electron, the muon, the tau particle, and their respective neutrinos (the electron neutrino, the muon neutrino, you get the idea). One of these six, as you may be able to recognize, is one of the particles in the atom. The electron is actually the only particle of the atom that is a fundamental particle (you will see why in a minute). It is also the most commonly occurring of the leptons, as the others break down quickly and are unstable.

Quarks are fermions that have fractional charges (meaning that instead of having a +1 charge, they have a +2/3 charge). There are six different types of quarks: the up quark, the down quark, the charm quark, the strange quark, the top quark, and the bottom quark. The up, charm, and top have a +2/3 charge, and the down, strange, and bottom quark all have a -1/3 charge. The only differences between each type of quark is that the charm quark is more massive than the up quark, the top quark is more massive than the charm quark, and the same applies for the other set (in the respective order).

Do you remember how I mentioned earlier that the electron is the only fundamental particle in the atom? Well, that is because the neutron and the proton are both formed of these quarks. The proton is composed of two up quarks and one down quark (resulting in an overall charge of +1), and the neutron is composed of one up quark and two down quarks (thus resulting in an overall charge of 0). The addition of the

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