Physics Review Notes Sean Magner and Peter Hazel Format: Question slide, then answer/explanation slide; use as notecards
Question 1: List (in order) and describe the 6 major models of the atom.
Atomic Structure • (Note: Democritus was the first to coin the term atom, but it was theoritical) • Dalton: 1800's: Discovered atoms: Decided they were just tiny balls of matter • Thomson: 1897: Plum pudding: discovery that atoms had different charges, developed model that atoms were ball of positive material, and had spots of negative charge scattered throughout it • More on next slide ==>
Atomic Structure • Rutherford: 1911: Discovery that atoms were mostly empty space, developed idea of small, compact, positive nucleus, later discovered and named protons • Bohr: 1912: 2 discoveries: RULE 1: Electrons can orbit only at certain allowed distances from the nucleus. RULE 2: Atoms radiate energy when an electron jumps from a higher-energy orbit to a lower-energy orbit. Also, an atom absorbs energy when an electron gets boosted from a low-energy orbit to a high-energy orbit. • Chadwick: 1932: Discovered the neutron • Electron Cloud Model: Around 1927: Multiple discoveries by several scientists: It is impossible to predict exactly where an electron will be at any given time, but you can predict a general area where it may be, instead of strict orbitals, the atom has "clouds"
Question 2 What is the Rutherford (or Geiger-Marsden) experiment? Why was it important?
Gold-Foil Experiment Otherwise known as the "Gold-Foil Experiment," 2 scientists Geiger and Marsden (under Rutherford's direction) fired atoms at a high speed at a sheet of gold foil, expecting most of them to bounce off in different directions. Instead, most of the atoms passed right through the foil unaffected, and they discovered that atoms were mostly empty space. Some of the particles were deflected off in different directions, indicating that there was some central body of mass (the nucleus), that could collide with other nuclei.
Question 3 Explain how electrons are transferred between orbitals within an atom. What are atomic spectra?
Atomic Spectra Basically, electrons in an atom are bound to the nucleus, and so they have to absorb or release energy to go up or down a layer, or transfer between orbitals. The atomic spectra is the the color or frequency of the photon emitted when an electron goes up or down a level.
Question 4: What are emission spectra and absorption spectra?
Emission and Absorption Spectra • Emission spectra are produced by thin gases where atoms don't collide very often. The emission lines match up with photons of specific energies that are released when excited atoms in the thin gas lose energy and go back down to a lower level. • Absorption spectrum are produced when light passes through a cold, dilute gas and the atoms absorb energy at specific frequencies; since the light probably won't be emitted in the same direction as the photon, this creates dark lines in the spectrum.
Question 5: What are nuclides, nucleons and isotopes?
Nuclear Structure - Terms • Nuclide-atomic species characterized by a specific number of protons and neutrons • Isotopes-atoms that contain the same number of protons and different numbers of neutrons (isotopes are a type of nuclide) • Nucleon- Protons and Neutrons, the particles that make up the nucleus
Question 6: • Explain/Give an example of proper Atomic notation. How do you label the following? • -Normal Carbon • -Carbon Isotope with one more neutron • -Normal Uranium • -Normal Platinum • -Normal Mercury
Atomic Notation • Top number is total number of nucleons, bottom is number of protons. • 612C carbon -12 • 613C carbon -13 • 92238U uranium - 238 • 78198Pt platinum -198 • 80198Hg mercury - 198
Question 7: • What is strong nuclear force? • How are atomic number and neutron number related to nucleus stability?
Nuclear Structure - Force • Strong nuclear force • Because all protons are positive they must be constantly repelling each other • Strong force keeps the nucleus from breaking apart • Gravitational attraction of nucleons is not great enough to hold nucleus together • Very short range, only observed inside the nucleus • Likely involves neutrons as well • large nuclei need proportionally more neutrons in order to have a stable nucleus
Nuclear Structure - Stability • For atoms with small nuclei the number of protons usually equals the number of protons • Large nuclei have more neutrons than protons
Question 8: Define and list the important properties of the three different types of radiation. (Hint: most important property of all forms is ionization.)
Radioactivity - Ionizing Properties • Radioactive decay involves one of three possible radiations • Alpha, beta, or gamma • All three ionize • When radioactive particles pass through substance they cause electrons to be removed from the atoms. • Atoms that have lost electrons are called ions
Question 9: List some of the effects of exposure to radiation? Which type of radiation is most dangerous?
Properties of Radiation • Penetration ability • Alpha-low, Beta-Medium, Gamma-high • Typical path length in air • A-a few centimeters, B-less than a meter, G-infinite • Speed • A=107m/s, B=108m/s, G=3*108m/s • Most to least dangerous • A, B, G • Material needed to absorb/stop • A=piece of paper, B=a few mm of aluminium, G=10cm of lead
Question 10: Explain alpha decay, and how it appears mathematically in the atomic equations.
Alpha Decay • α (alpha) particles are helium nuclei • 24α = 24He2+ • In alpha decay nucleus loses components of alpha particles • 95241Am => 93237Np + 24α
Question 11: Explain beta decay, and how it appears mathematically in the atomic equations.
Beta Decay • Beta particles are actually just electrons: • -10β or -10e • Electron is formed when a neutrino decays, antineutrino is emitted • 01n => 11p + -10β + • Antineutrino has no charge and virtually no mass • 3890Sr => 3990Y + -10β +
Question 12: Explain gamma decay, and how it appears mathematically in the atomic equations.
Gamma Decay • Unlike alpha and beta gamma rays are part of the electromagnetic spectrum • After gamma decay, the nucleus has less energy but mass number and atomic number are unaffected • changed from excited state to lower energy state • ZAX => ZAX + 00γ
Question 13: What is a half life? How does it involve radioactive decay?
Half-Life • Time it takes for half the number of nuclides in a sample to decay • With half-life decay, substance will theoretically never completely disappear • Radioactive is random and is not affected by external conditions • no way of knowing whether a particular nucleus is going to decay within a certain window of time • gives chances of decay happening in a time window • Exponential process
Question 14: What are artificial transmutations? What is the unified atomic mass unit? What are mass defect and binding energy?
Nuclear Reactions • Artificial Transmutations: An artificially induced nuclear reaction caused by the bombardment of a nucleus with subatomic particiles or small nucei. • Unified Atomic Mass Unit (u or amu)- basic unit of mass used in calculating nuclear reactions, it is 1/12th the mass of a Carbon atom • More on next slide ==>
Nuclear Reactions • Mass Defect- When a nuclear reaction occurs, some energy is always released, and there is a mass defect, some mass is missing so it is not exactly balanced. That missing mass is actually the energy released. According to E=mc^2, mass can be turned into energy, and that is what happens in nuclear reactions. • Binding Energy- the binding energy released when a nucleus is assembled from its component nucleons
Question 15: Explain what fusion and fission are and how they work? Define binding energy per nucleon.
Fusion and Fission • -Fusion is a nuclear reaction where small nuclei are joined together into larger nuclei and release energy. Most fusion takes place in the sun and is the fusion of 2 different isotopes of hydrogen combining to produce helium. • -Fission is a nuclear reaction where large nuclei have small particles slammed into them and break up into smaller nuclei, releasing large amounts of energy.
Binding Energy per Nucleon Binding Energy per Nucleon: When a nuclear reaction releases energy, the products are in a lower energy state, usually due to mass loss. In order to compare those different nuclei, physicists compare the binding energy per nucleon. That is the total binding energy for the nucleus divided by the total number of nucleons.
Question 16: • Solve some of the following sample nuclear reaction questions: • How much energy would be released in the equation below? • 146C ==> 147N + 0-1β • Solution on page 63 of IB Physics Review Book