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--------------------------- 2557 - ELECTRON - just the fundamentals?
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- In 1887 J.J. Thomson at Cambridge University first studied the electron in a cathode ray tube. The cathode ray tube is what televisions used to be made of in the 1960‘s. Thomson learned that he could direct the negative beam of electrons using a magnetic field.
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- That is how he determined electrons had a negative charge, although the negative part was arbitrary, the electron could have just as easily been called positive. But, whatever the choice everything else follows. As we will see later, how much the electron’s path curved as a result of the magnetic field can be used to calculate the mass of the electron.
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- The amount of electric charge on one electron was first measured by Robert Millikan in his famous oil drop experiment of 1909. Each of the 100 elements in the Periodic Table are determined by the number of electrons surrounding the nucleus in shells, there are an equal number of protons in the atom if the atom has a neutral charge. This was in 1913.
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- In 1916 Gilbert Lewis explained how chemistry binding worked by using the electrons in the outer shell.
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- Particle physics defines the electron as one of the Leptons. Lepton is Greek leptos, meaning “thin“. There are six Leptons. Leptons are the class of particles that are not affected by the Strong Force that binds protons and neutrons together, which are made of Quarks.
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- So, all ordinary matter are either Leptons or Quarks. There are three varieties of electrons and three varieties of neutrinos depending on their energy levels, or mass.
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- Energy = mass * c^2, the speed of light squared. Therefore Mass = Energy / c^2. In physics Mass is often specified in electron volts / c^2, and often the c^2 is left off and just understood to be there. The three varieties of electrons are:
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-------------------------- Electron ------------ 511,000 electron volts /c^2.
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-------------------------- Muon ------------- 106,000,000 electron volts / c^2
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-------------------------- Tau Lepton --------- 1,777,100,000 electron volts / c^2
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- If you heat up an electron, giving it more energy, when it reaches 106,000,000 eV it turns into a Muon. The Muon is 207 times heavier or higher energy than the electron. The Muon quickly decays back into an electron, an Electron-antineutrino and a Muon-neutrino in 2.2 * 10^-6 seconds.
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- If you heat up a Muon to 1,777,100,000 eV it transitions into a Tau Lepton. The Tau Lepton is 3,478 times heavier than an electron and it decays in 2.9*10^-13 seconds.
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- All three have the same charge. The electron’s charge = -1.6 *10^-19 Coulombs.
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- The electron’s mass is 9.1*10^-31 kilograms. It takes 1,836 electrons to equal the mass of one proton.
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- The way the electron mass was calculated goes back to Thomson’s cathode ray tube. A magnetic field around the tube could curve the path of the electron beam. The curved path represented the path where the magnetic force exactly balanced the centrifugal force.
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-------------------------- Hev = m * v^2 / r
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-------------------------- e / m = v / H * r
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- “H” is the strength of the magnetic field. “r” is the radius of the curved path. “v” is the velocity of the electron which was determined to be 30,000 km/sec, or 10% the speed of light. ”e / m” is the charge to mass ratio for the electron and that worked out to be 1,836 times greater than that of the proton, the hydrogen ion.
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- Since the mass of the hydrogen ion was known the mass of the electron must be 1/1836 of that, or 9.1*10^-31 kilograms. The proton weighs 1.67*10^-27 kilograms.
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- Whenever electrons move there is a flow of “charge“. Whenever there is a moving charge a magnetic field is generated. The speed of electric current in a wire causing electric current in other parts of the wire is 75% the speed of light, 140,000 miles per second.
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- The radius of an electron inferred from its electric charge is 2.8*10^-15 meters. An atom is 10^-10 meters. So, the electron is 1/10,000th the size of the atom.
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- The speed of an electron in a vacuum can approach but never exceed the speed of light. In a particle accelerator at Stanford University the energy of an electron has reached 51,000,000,000 electron volts. The linear particle accelerator has taken the electron’s velocity to 0.999,999,999,950 the speed of light.
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- If a photon is given enough energy it will turn into a electron - positron pair. The photon is a “Gamma Ray” at that energy, 1,020,000 electron volts. Matter-antimatter are created out of pure energy. Just like in the Big Bang.
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- The average density of electrons in the Universe is 1 electron per cubic meter. Therefore, there are 10^79 electrons in the Universe. There must also be 10^79 protons in the Universe as well because the Universe is electrically neutral. We think.
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- In introducing the Periodic Table we mentioned that the electrons travel around the nucleus in shells. Why is the atom structured to have shells and what determines how many electrons are in each shell?
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- The answer starts with the Pauli Exclusion Principle which states that no two electrons can share the same energy level. Pauli formulated his theory in 1927 and proved it with spin-statistics in 1940.
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- The second part of the answer has to do with the dual nature of the electron being both a wave-like particle and a particle-like wave. The wavelength of the electron is equal to Planck’s Constant of Action / the electron’s angular momentum, w = h / p. Or, momentum, p = h / w. Momentum is proportional to the inverse of wavelength. And, momentum is directly proportional to the frequency of the wave. The higher the energy the higher the frequency and the smaller the wavelength.
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- Pauli determined that all particles with an integer multiple of h / 2*pi spin are Bosons. Spin, or angular momentum, is equal to the number of the shell *2pi, p = n* h /2 pi. 2pi is 360 degrees or one cycle of a wavelength. And, that all particles with a ½ integer multiple of h/2*pi spin are Fermions.
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- Electrons are Fermions and have ½ integer spins. “n” is the number that represents the various shells an electron can have around the nucleus of an atom. There are 2 electrons in an atoms lowest, or first energy shell. Since due to the exclusion principle they can not occupy the same energy state, one of the electrons must be spinning clockwise and the other electron spinning counterclockwise.
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- The successive shells are all multiplies by successive squares of this configuration: 2*1 = 2 in the 1st shell, 2*4 = 8 in the second shell, 2*9=18 in the third shell, and 2*16 = 32 electrons in the 4th shell. This configuration goes all the way up through the Periodic Table.
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- Helium has 2 electrons in the first shell. Sodium has 2 in the first, 8 in the second and 1 in the third. Arsenic has 2 in the first, 8 in the second, 18 in the third , 2 in the forth, and 3 in the fifth shell. Lead has 2 in first, 8 in second, 18 in third, 32 in forth, 18 in the fifth, 4 in the sixth shell.
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- The progression continues until each shell is full according to the formula that allows electrons to form standing waves of complete wave cycles in each shell. However, the further the electrons are away from the nucleus the more lightly they are held. Once you get past Uranium that has 92 electrons the atoms become radioactive and decay into the lower level elements that have fewer electrons.
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- We understand electron behaviors very well, or we could not invent all the technology that we enjoy. However, we are still learning more about the quantum physics that causes electrons to have those behaviors.
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- Other Reviews available;
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- 507 - “What is an Electron. The Lorentz Factor”
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- 730 - “ Antimatter”
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- 1226 - there are 3 generations of electrons.
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- 1652 - electrons are all round us.
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- 2232 - what is the shape of an electron?
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- 2373 - what is an electron?
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- 2495 - electron’s best description imagined
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- December 23, 2019 2557 731
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--------------------- Monday, December 23, 2019 --------------------
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