There are two categories of fermions, quarks and leptons. Each of these categories classifies six types of particles. If a fermion interacts through what is labeled the color charge then it is a quark, otherwise it is a lepton.
Quarks and Color Charge
Quarks themselves appear structureless and interact through all four of the known forces. They are believed to be truly fundamental. Each has a mass and exhibits spin, and they are always found in combination with other quarks (or anti-quarks).
Each quark has an electric charge of +2/3 or -1/3. These charges determine how composite particles can be formed. The resulting charge of the composite particle is always either a -1, 0, or +1.
Quark color charges come in red, green, and blue (and anti-red, anti-green, and anti-blue). A quark's color can be changed by gluons, and when they combine the resulting color always add up to white.
The white color is produced with the combination of red, green, and blue quarks. White is also produced by anti-quark unions (red and anti-red).
Quark Flavors and Generations
The six types, or flavors, of quark are: up, down, charm, strange, top, and bottom. Only the up and down quarks are stable, meaning that they can exist for long periods of time without changing form (unless there is a collision).
Quarks come in one of three generations. The up and down quarks constitute the first generation, the charm and strange make up the second generation, and the top and bottom are third generation.
Lepton Types and Generations
The six types leptons are the electron, electron neutrino, muon, muon neutrino, tau, and tau neutrino. All leptons have a +1/2 spin and negative charge. Though lepton flavors are not necessarily preserved in original form, the overall lepton number is conserved through interactions.
Leptons are, like fermions, also categorized into three generations. The electron and electron neutrino constitute the first generation, the muon and muon neutrino comprise the second generation, and the tau and tau neutrino make up the third generation.
Characteristics of Leptons
Electrons are responsible for chemical bonding, and they are a fundamental constituent of higher-order composites called atoms. Electrons absorb and emit radiation in the form of photons.
Electrons are the lightest stable subatomic particles known. Their electrical charge is the base criterion of electricity.
Muons have a mass roughly 207 times of the electrons. Sometimes referred to as mu-mesons, the muon is in fact purely a lepton. All known natural muons are produced by cosmic rays.
The tau are the only leptons capable of decaying into a group of composite particles called hadrons. The tau can also decay into muons.
Neutrinos lack an electric charge, and they pass through ordinary matter almost completely unperturbed or detectable. Trillions are passing through every person right now, many directed from our sun.
How Atoms Are Created
Quarks combine to form nucleons, the center of atoms. Two up quarks and one down quark make up the proton, and two down quarks with one up quark make up the neutron.
Electrons surround nucleons in clouds, and the final formation is called an atom. Atoms bond and form molecules; once a certain level of complexity is reached, organic compounds are created. From that point, according to certain models, it is only a matter of progressing organization before life is reached.
General References
1. Sakurai, J.J. Modern Quantum Mechanics
2. Herbert, Nick. Quantum Reality
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