James Linzel's List: Atomic Theory

• protons and neutrons

• Even though you cannot see a basketball, you can assume that one person threw  a basketball to the other person because you see its effect on the people.
• It turns out that all interactions which affect matter particles are due to an exchange of force carrier particles, a different type of particle altogether. These particles are like basketballs tossed between matter particles (which are like the basketball players)

• The carrier particle of the electromagnetic force is the photon ().  Photons of different energies span the electromagnetic spectrum of x rays, visible light, radio waves, and so forth.

  • A picture of the electromagnetic spectrum can be seen at:
    
    <a target="_blank" href="http://mynasadata.larc.nasa.gov/images/EM_Spectrum3-new.jpg">http://mynasadata.larc.nasa.gov/images/EM_Spectrum3-new.jpg</a>
    
    
    

• The best known lepton is the electron (e^-)
• Quarks are sociable and only exist in composite particles with other quarks, whereas leptons  are solitary particles.

• All visible matter in the universe is made from the first generation of matter particles -- up quarks, down quarks, and electrons. This is because all second and third generation particles are unstable and quickly decay into stable first generation particles.

• But what are protons, neutrons and electrons made from?
• Electrons are believed to be fundamental point-like particles with no further constituents. They are a member of a class of particles called leptons. However, protons and neutrons are both made from smaller particles called quarks. There are six different types of quark, which are believed to be fundamental. Only two of these, however, are needed to explain protons and neutrons. The proton is made from two up quarks and one down quark; the neutron consists of one up and two down quarks.
• Every part of the universe that we see during our everyday lives can be explained with only these particles.
• In the standard model, matter is made up of two classes of elementary particles: leptons, which include electrons, muons and neutrinos; and quarks, which come in six varieties and stick together in twos or threes to form heavier particles such as protons, neutrons and pions.

  • Ignore the anti-matter particles. We don't want to confuse the matter.
• The standard model does not just explain matter. It also explains the forces of nature. Both matter and forces are explained using particles. All these particles fit into two categories: fermions and bosons. Fermions are the quarks and leptons that make up matter; bosons include the photon and other particles associated with forces.

• The table below lists all the fermions in the standard model. (The range of names is due to the varying imagination of physicists.)

  Fermions
  Leptons			Quarks
  e - electron	μ - muon	τ - tau	u - up quark	s - strange quark	t - top quark
  νe - electron neutrino	νμ - muon neutrino	ντ - tau neutrino	d - down quark	c - charm quark	b - bottom quark

  • The only parts of this table you really need to remember are the electron, and the up and down quarks that form protons and neutrons.
• The great success of the standard model is that it explains how fundamental particles interact with each other. Particles interact by four fundamental forces: gravity, electromagnetism, the strong nuclear force and the weak nuclear force.
• BosonsForceCarrier particlesElectromagneticγ - photonWeak nuclearW⁺, W^-, Z⁰Strong nuclearg - gluonGravity?graviton?

  • Simply know that photons transmit the force of electromagnetism and that gluons are responsible for the strong nuclear force that holds neutrons and protons together.
• The strong nuclear force is what holds the nucleus of an atom together. As the nucleus contains only protons (with positive charge) and neutrons (with zero charge), the electromagnetic force would cause it to fly apart.
• the strong force has a very short range, so it plays no role in larger scale objects.

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