| MadSci Network: Physics |
The atom is composed of a nucleus surrounded by a cloud of electrons. The cloud of electrons has a radius of about 1 Angstrom (10^-10 meters). The electron is a "lepton", the name given to a class of light elementary point particles that do not have strong interactions. The electron is the only lepton that is an important part of an atom. The electrons are bound to the nucleus by the Coulomb electric force between the positively charged nucleus and the negative electrons. You could consider virtual photons as particles that carry th eCoulomb force between charged particles. "Vitual" particles travel between the other particles carrying the force, but wouldn't show up on photograph. The nucleus has a radius of 1.2 X A^(1/3) fm (10^-15 meters). The nucleus is composed of Z protons and N neutrons. The mass number of a nucleus is denoted as A=Z+N. The protons and neutrons are "hadrons", the name given to particles with strong interactions. The strong interaction is about 100 times stronger than the electromagnetic interaction, but has a short range of about 1.4 fm. The neutron and proton have a radius of about 0.8 fm. The nucleus can be thought of as a liquid drop with the protons and neutrons moving about like the molecules in a liquid. The neutrons and protons themselves are composite particles composed of 3 quarks. The quarks are strongly interacting point particles, held together by springlike forces produced by gluons. The gluons themselves are not present, but are "virtual" particles that produce the force between quarks. The process by which this happens is a "Quantum Field Theory" (QFT) called "Quantum ChromoDynamics" (QCD). These concepts are very advanced (but well established) and well beyond anything you should consider for your project. I just mention them here for completeness. Similarly the Coulomb force between charges is caused by virtual photons in a process called "Quantum Electrodynamics" (QED), also beyond what you shuld consider. For your purposes the force holding the 3 quarks together could be represented by 3 springs between each pair of quarks. A little more detail about the quarks: They come in three colors, so that one is red, one green, and one blue. [These are not real colors, but are used to distinguish the three types.] You could color them that way in any picture. The proton is composed of 2 "u-quarks" and 1 "d-quark". The neutron of 2 d-uarks and 1 u-quark. [The u stands for "up" and the d for "down", which is how the quarks are sometimes repressented. The u-quark has a charge + (2/3)e, and the d-quark a charge -(1/3)e, where e is the magnitude of the electron charge. You can add these charges up to see that this gives the proton a charge of +e and the neutron zero charge. There are other types of quark, but only the u and d quarks are important for the proton and neutron. I hope this has not been too complicated for you. I don't know exactly what is meant by "5 components in an atom other than protons, electons, and neutrons." Maybe the quarks are counted as three components because of three colors. But then there would be six, namely uR, uG, uB, and dR, dG, dB. Perhaps they mean gluons as a component, represented as the springs. Also some nuclear models include pions as well as the protons and neutrons. Pions are strongly interacting particles with a mass about 1/7 that of a proton. They travel between the protons and nucleons, helping to bind them together. There are three different pions, charged +, -, and zero. Some models of the proton and neutron include a "sea" quark-antiquark pairs. The antiquarks could be another component. Again, where they came up with "5 components" is to clear to me. Let me know if there is anything detailed you want to know about any of the above, but I think there should be enough to work with. Too much detai would get even morre confusing.
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