Name: Date: Modern Physics Models of the Atom The word atom comes from the Greek word atomos meaning indivisible We now know that this model of the atom is not accurate JJ Thompson Experiment and atomic model Discovered the electron Proposed Plum Pudding model of the atom Ernest Rutherford Experiment & Changes to the Atomic Model Gold foil experiment shot alpha particles at thin gold foil barrier Niels Bohr Contribution to Atomic Model Atomic emission & absorption spectra Electrons can only exist in specific orbits 1
Atoms only emit certain colors of light What is a photon? Energy of a photon: E photon = 1. A photon of light with a frequency of 6 x 10 14 Hz is emitted from a light source. What is the energy of the photon in Joules? 2. An electromagnetic wave with a wavelength of 1.5 x 10-8 meter is emitted from an atom. What is the energy of the photon in Joules? Application: Atomic Spectra So what? Atoms can only absorb or emit photons with a certain energy level. Each energy corresponds with a certain frequency (or color). Hot gasses emit photons of a certain color Cold gasses absorb photons of the same color. Astronomers use this to determine the chemical properties of distant stars and planets! 2
When an electron changes energy levels, it either gains or loses a photon. When an electron moves up in Energy Levels energy, a photon is absorbed (gained) When an electron moves down in energy, a photon is emitted (lost) is the lowest energy level. The ground state occurs when an electron is completely free from an atom (highest energy level) An electron can only exist at these energy levels, and not in between. Energy of a photon: E photon = 3. An electron in Hydrogen moves from its ground state to the n=3 state. a. Is a photon absorbed or emitted by the atom? b. Calculate the energy of the photon in ev. c. Calculate the energy of the photon in J. 4. A photon with a wavelength of 2.29 x 10-7 meter strikes a mercury atom in the ground state. a. Calculate the energy in Joules of the photon b. Determine the energy in electron-volts of the photon c. Based on your answer to the previous question, can this photon be absorbed by the mercury atom? 5. A hydrogen electron moves from the n=3 state to the ground state. This process emits a photon or photons. How many possible photons can be emitted? 3
The Dual Nature of Light & Matter Evidence that light is a wave Young s Double Slit Evidence that light is a particle Compton Scattering Photoelectric Effect Evidence that matter is a wave Louis de Broglie Evidence that matter is a particle Why don t we see the wave-nature of matter in everyday life? 6. Wave-particle duality is most apparent in analyzing the motion of 1. a baseball 2. a space shuttle 3. a galaxy 4. an electron 7. Which phenomenon provides evidence that light has a wave nature? 1. emission of light from an energy-level transition in a hydrogen atom 2. diffraction of light passing through a narrow opening 3. absorption of light by a black sheet of paper 4. reflection of light from a mirror 8. Light demonstrates the characteristics of 1. particles, only 2. waves, only 3. both particles and waves 4. neither particles nor waves 9. On the atomic level, energy and matter exhibit the characteristics of 1. particles, only 2. waves, only 3. neither particles nor waves 4. both particles and waves 10. Which phenomenon best supports the theory that matter has a wave nature? 1. electron momentum 2. electron diffraction 3. photon momentum 4. photon diffraction 11. Moving electrons are found to exhibit properties of 1. particles, only 2. waves, only 3. both particles and waves 4. neither particles nor waves 4
Conservation of Mass-Energy E = 12. According to mass/energy equivalence, how much energy is stored in a 0.20 kg notebook? 13. In a chemical reaction, 242,000 Joules of energy are released. How much mass is converted to energy in this reaction? The Universal Mass Unit 14. How much energy, in megaelectronvolts, is produced when 0.350 universal mass unit of matter is completely converted into energy? 15. In a nuclear reaction, 8.5MeV of energy is released. How many universal mass units does this represent? Pair Production When energy is converted into matter, charge is conserved Charge is created in positive/negative pairs Antiparticle same mass opposite charge of typical particle Particle-Particle Annihilation When a particle meets its antiparticle, the two both annihilate and become pure energy 16. An electron and a positron (the electron s antiparticle) collide and both are annihilated as a result. How much energy is created in this collision? 17. How much energy would be required to create 3 protons and 3 anti-protons? 18. A particle has a mass of 1.67x10-27 kg and a charge of -1.6x10-19 C. What type of particle is it? 5
Nuclear Reactions In all nuclear reactions, and must be conserved. 15. During the process of a Beta emission, a neutron in the nucleus of an atom is converted into a proton, an electron, an electron antineutrino, and energy. Neutron proton + electron + electron antineutrino + energy Based on conservation laws, how does the mass of the neutron compare to the mass of the proton? Since charge must be conserved in the reaction shown, what charge must an electron antineutrino carry? Binding Energy and Mass Defect When protons and neutrons come together to form a nucleus, it is observed that the actual mass of the nucleus is than the mass of the individual particles that make up the nucleus This "missing mass" is known as the A small quantity of the mass of the particles is converted into to keep the nucleus together Anti-matter Antimatter is just like ordinary matter, but with opposite charge You could build an entire universe out of antimatter! An anti-electron (positive) orbiting an anti-proton (negative) would make an anti-hydrogen. 2 anti-hydrogens and an anti-oxygen could make anti-h 2 O. Everything in this universe would behave exactly like ours - opposite charges would attract and like charges would repel. But this universe couldn't coexist with ours - if antimatter comes in contact with ordinary matter, they annihilate each other and become PURE ENERGY (via E=mc 2 )! How much energy is there in antimatter? Fuel Joules from 1 kg fuel Mass (kg) converted to energy % Gasoline (chemical energy) 5 x 10-10 kg Uranium (nuclear energy) Hydrogen (nuclear energy) 6.4 x 10 14 J 0.0009 kg Matter/antimatter annihilation 1 kg 100% 6
The Standard Model The standard model is the current model for all matter/particles and how they interact. The Fundamental Forces of Nature Force Force Force Force Classification of Matter / Particles of the Standard Model Matter Leptons Hadrons 7
Quarks Baryons Mesons Antiquarks Proton Neutron Electron 19. Name the fundamental interaction that best fits the following descriptions: The weakest interaction The strongest interaction Responsible for nuclear decay Acts between nucleons Only acts over very short distances Is responsible for like charges repelling Is related to the binding energy of a nucleus 20. Can a particle consisting of 3 up quarks exist? If so, what charge would it have? 21. What is the charge of the meson containing an up quark and an anti-down quark? 22. A subatomic particle is made of 2 strange quarks and 1 bottom quark. a) What is the charge of this particle? b) What is the classification name of this subatomic particle? 23. What is the charge of a baryon consisting of 2 anti-strange quarks and 1 anti-charm quark? 24. What is the charge of a meson consisting of a top quark and an anti-charm quark. 8
Problems 25. The strong force is the force of 1. repulsion between protons 2. attraction between protons and electrons 3. repulsion between nucleons 4. attraction between nucleons 26. The tau neutrino, the muon neutrino, and the electron neutrino are all 1. leptons 2. hadrons 3. baryons 4. mesons Base your answers to questions 27 and 28 on the information below. A lambda particle consists of an up, a down, and a strange quark. 27. A lambda particle can be classified as a 1. baryon 2. lepton 3. meson 4. photon 28. What is the charge of a lambda particle in elementary charges? 29. According to the Standard Model, a proton is constructed of two up quarks and one down quark (uud) and a neutron is constructed of one up quark and two down quarks (udd). During beta decay, a neutron decays into a proton, an electron, and an electron antineutrino. During this process there is a conversion of a 1. u quark to a d quark 2. d quark to a meson 3. baryon to another baryon 4. lepton to another lepton 30. Which statement is true of the strong nuclear force? 1. It acts over very great distances 2. It holds protons and neutrons together 3. It is much weaker than gravitational forces 4. It repels neutral charges 31. Which combination of quarks could produce a neutral baryon? 1. cdt 2. cts 3. cdb 4. cdu 32. A meson may not have a charge of 1. +1e 2. +2e 3. 0e 4. -1e 33. The charge of an antistrange quark is approximately 1. +5.33 10-20 C 2. -5.33 10-20 C 3. +5.33 1020 C 4. -5.33 1020 C 34. Compared to the mass and charge of a proton, an antiproton has 1. the same mass and the same charge 2. greater mass and the same charge 3. the same mass and the opposite charge 4. greater mass and the opposite charge 35. According to the Standard Model of Particle Physics, a meson is composed of 1. a quark and a muon neutrino 2. a quark and an antiquark 3. three quarks 4. a lepton and an antilepton 36. A particle unaffected by an electric field could have a quark composition of 1. css 2. bbb 3. udc 4. uud 37. A lithium atom consists of 3 protons, 4 neutrons, and 3 electrons. This atom contains a total of 1. 9 quarks and 7 leptons 2. 12 quarks and 6 leptons 3. 14 quarks and 3 leptons 4. 21 quarks and 3 leptons 9
Review Checklist Demonstrate understanding of energy quantization 1. Explain why an atom of a given element can produce only specific photons of light when heated. Demonstrate understanding of wave/particle duality of and matter 2. Light exhibits properties of (a) waves only (b) particles only (c) both waves and particles 3. Which phenomenon best supports the theory that light has a particle nature? a. electron momentum b. electron diffraction c. photon momentum d. photon diffraction 4. Which of the following could be used to demonstrate the wave properties of matter? a. asteroid b. electron c. bicycle d. proton e. apple Demonstrate understating of photon properties. Use equation to determine photon energy, frequency, and/or wavelength. Use EM Spectrum Chart to determine photon type. 5. What is the energy of a photon with a frequency of 2.5 x 10 13 hertz? 6. What is the wavelength of a photon with an energy of 3.0 x 10-18 joules? 7. What type of photon has an energy of 9.0 x 10-19 joules? Demonstrate understanding of mass/energy duality. Use equation to determine relationship between energy and mass. Be able to convert between universal mass units and mega-electron-volts. 8. How much energy is contained in 3.0 kilograms of matter? 9. How much mass is needed to produce 2.0 mega-joules of energy? 10. How much energy is contained in 5.0 universal mass units of matter? Determine ionization energies and kinetic energies for liberated electrons 11. What energy is needed to liberate an electron from the c-level of a mercury atom? 12. A hydrogen atom with an electron in the n = 3 level is hit by a photon with an energy of 2.51 electron-volts. What kinetic energy will the electron have as it leaves the atom? Use equation to determine the outcome of a photon absorption, emission, or an energy level transition. Convert from joules to electron-volts; determine photon energy and/or frequency and type using the EM Spectrum Chart. 13. A photon causes an electron to jump from the b-level to the e-level of a mercury atom. What energy did this photon need to have? What was its frequency? What type of photon was it? 14. A 10.2 ev photon is emitted by an electron in a hydrogen atom as it returns to the ground state. What energy level did the electron drop from? 15. What photon energy is needed to cause an electron to leave the h-level of a mercury atom with a kinetic energy of 4.0 electron volts? 16. An electron in the d-level of a mercury atom drops to the ground state. How many different photons could be produced during this transition? 10
17. Explain why a 3.0 electron-volt photon will have no effect on an electron in the n=2 level of a hydrogen atom. Understand the importance and meaning of the emission and absorption spectrum. Identify the components of a sample by its spectrum. 18. Use the spectrums below to determine which of the four samples contain Element X. Classify and determine the charge of various particles. Explain how matter and anti-matter are related. Describe the fundamental forces of the Standard Model. 19. Classify each of the following as either a: lepton, anti-lepton, baryon, antibaryon, meson or not enough information. (1) A particle made of 3 quarks. (2) A particle with no charge. (3) An electron. (4) A neutron. (5) A particle composed of an up quark and an anti down quark. (6) A particle composed of three anti-up quarks. (7) A muon-neutrino. (8) A particle with a charge of +2. (9) An anti-electron. 20. What is the charge on a particle containing two down quarks and one up quark? 21. What is the charge on a particle containing a down quark and an anti-up quark? 22. A hydrogen atom consists of a proton and an electron. An anti-hydrogen atom consists of an antiproton and an anti-electron (positron). Explain the differences and similarities between hydrogen and anti-hydrogen in terms of mass, charge, and emission spectrum. 23. Which of the particles would not be effected by the electromagnetic force? (1) electron (2) antimuon (3) tau-neutrino (4) ucb (5) udd 24. Which of the particles would not be effected by the strong force? (1) proton (2) meson (3) electronneutrino (4) muon 11
Answers: 1. Energy levels are quantized 2. C 3. C 4. B,d 5. 1.66 x 10-20 J 6. 4.52 x 10 15 Hz 7. Ultraviolet 8. 2.7 x 10 17 J 9. 2.2 x 10-11 kg 10. 4655 MeV 11. 5.52 ev 12. 1 ev 13. -2.03 ev / 3.2 x 10-19 J / 4.8 x 10 14 Hz / visible 14. N=2 15. -5.57 ev 16. 6 (d->c, c->b,b->a,d->b,c->a,d->a) 17. Would take you to -0.4 ev, which is not an energy level 18. A,D 19. B,X,L,B,M,anti-B,L,B,anti-L 20. 0e 21. -1e 22. Same in all ways (overall charge is same, but individual charge is different) 23. 3,5 24. 3,4 12