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AP Notes Chapter 2

AP Notes Chapter 2. History of the atom Summed-up. Greeks Democritus and Leucippus - atomos Aristotle- elements. Alchemy 1660 - Robert Boyle- experimental definition of element. Lavoisier- Father of modern chemistry. Atoms and Elements. Dalton’s Atomic Theory.

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AP Notes Chapter 2

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  1. AP Notes Chapter 2 History of the atom Summed-up • Greeks • Democritus and Leucippus - atomos • Aristotle- elements. • Alchemy • 1660 - Robert Boyle- experimental definition of element. • Lavoisier- Father of modern chemistry. Atoms and Elements

  2. Dalton’s Atomic Theory • Elements are made up of atoms • Atoms of each element are identical. Atoms of different elements are different. • Compounds are formed when atoms combine. Each compound has a specific number and kinds of atom. • Chemical reactions are rearrangement of atoms. Atoms are not created or destroyed.

  3. The Atom • Dalton (early 1800s) indivisible

  4. A Helpful Observation • Gay-Lussac- under the same conditions of temperature and pressure, compounds always react in whole number ratios by volume. • Avagadro- interpreted that to mean • at the same temperature and pressure, equal volumes of gas contain the same number of particles. • (called Avagadro’s Hypothesis)

  5. Experiments & theories to determine what an atom was • John Dalton- atoms indivisible • J. J. Thomson- Cathode ray tubes, electrons • Marie Curie- radioactivity • Robert Millikan- electron mass & charge • Ernest Rutherford- protons • James Chadwick- neutrons

  6. Voltage source Thomson’s Experiment - +

  7. Voltage source Thomson’s Experiment - +

  8. Voltage source Thomson’s Experiment - + • Passing an electric current makes a beam appear to move from the negative to the positive end.

  9. Voltage source Thomson’s Experiment • By adding an electric field

  10. Voltage source Thomson’s Experiment + - • By adding an electric field, he found that the moving pieces were negative

  11. The Atom • Thompson (~ 1900) . . . cloud of (+) charge . . . . . . electron(-) charge . “plum pudding” model

  12. Thomsom’s Model • Found the electron. • Couldn’t find positive (for a while). • Said the atom was like plum pudding. • A bunch of positive stuff, with the electrons able to be removed.

  13. Atomizer Oil droplets + - Oil Telescope Millikan’s Experiment

  14. Millikan’s Experiment X-rays X-rays give some electrons a charge.

  15. Millikan’s Experiment • Some drops would hover From the mass of the drop and the charge on the plates, he calculated the mass of an electron

  16. Radioactivity • Discovered by accident • Henri Bequerel – photographic plates • Marie Curie – studied & named it • Three types • alpha- helium nucleus (+2 charge, large mass) • beta- high speed electron • gamma- high energy light

  17. James Chadwick • Neutrons • Particles from radioactive polonium hit a beryllium target and produced particle • no charge • slightly greater mass than the proton

  18. Rutherford’s Experiment • Used uranium to produce alpha particles. • Aimed alpha particles at gold foil by drilling hole in lead block. • Since the mass is evenly distributed in gold atoms alpha particles should go straight through. • Used gold foil because it could be made atoms thin.

  19. Rutherford’s Experiment Florescent Screen Lead block Uranium Gold Foil

  20. Rutherford’s Experiment What he expected

  21. Rutherford’s Experiment Because

  22. Rutherford’s Experiment Because, he thought the mass was evenly distributed in the atom.

  23. Rutherford’s Experiment What he got

  24. + Rutherford’s Experiment How he explained it • Atom is mostly empty • Small dense, • positive pieceat center. • Alpha particlesare deflected by it if they get close enough.

  25. + Rutherford’s Experiment

  26. Gold Foil Experiment • Rutherford (~1911) Nuclear Model heavy central(+) nucleus . . . . . . . . . . e- “about”nucleus

  27. The Atom • Rutherford (~ 1911) . heavy central(+) nucleus . . . . . . (e-) aboutnucleus Nuclear Model

  28. The Atom . • Bohr (~ 1913) . . . . e- inallowed orbits central (+)nucleus . . . n=3 . n=2 . . . n=1 Planetary Model

  29. Modern View • The atom is mostly empty space. • Two regions • Nucleus- protons and neutrons. • Electron cloud- region where you might find an electron.

  30. The Atom • Heisenberg, de Broglie, Schroedinger (mid 1920s) . . . . . . . e- in regionsdefined by mathfunctions . . . . Quantum Mechanical Model

  31. Sub-atomic Particles • Z - atomic number = number of protons determines type of atom. • A - mass number = number of protons + neutrons. • Number of protons = number of electrons if neutral.

  32. Nuclear Symbols & Notation A X Mass Number→ ←Element Symbol Z Atomic Number→ 23 24 Na Na 11 11

  33. Isotopes of elements • Isotopes are forms of an atom that differ by the number of neutrons • Mass number is approximation of exact atomic mass of an isotope • Atomic mass or atomic weight is the average mass of the isotopes of atoms • Isotopic percent abundance or fractional abundance is a description of the proportion of an isotope in a sample of an element

  34. Atomic Mass • Atoms are so small, it is difficult to discuss how much they weigh in grams. • Use atomic mass units. • an atomic mass unit (amu) is one twelth the mass of a carbon-12 atom. • This gives us a basis for comparison. • The decimal numbers on the table are atomic masses in amu.

  35. They are not whole numbers • Because they are based on averages of atoms and of isotopes. • can figure out the average atomic mass from the mass of the isotopes and their relative abundance. • add up the percent as decimals times the masses of the isotopes.

  36. Isotopes of Hydrogen hydrogen deuterium tritium

  37. Examples • There are two isotopes of carbon 12C with a mass of 12.00000 amu(98.892%), and 13C with a mass of 13.00335 amu (1.108%). • There are two isotopes of nitrogen , one with an atomic mass of 14.0031 amu and one with a mass of 15.0001 amu. What is the percent abundance of each?

  38. Percent Abundance Percent abundance = number of atoms of a given isotope x 100% total number of atoms of all isotopes Fractional Abundance Fractional abundance = Percent Abundance 100% Atomic Weight = (abundance isotope 1)(weight isotope1) + (abundance isotope 2)(weight isotope2)… or

  39. A portion of an atom’s mass of protons, neutrons and electrons is converted to energy that holds the atom together. • Einstein gave us ΔE = (Δm)C2 • The loss of this mass as the atom forms is called the mass defect. This missing mass is converted to “binding energy” (BE) • Mass atom = BE + #pro. + #elec. + #neu.

  40. Allotrope Different forms of the same element that exist in the same physical state under the same conditions of Temperature & Pressure Carbon • Diamond • Graphite

  41. Graphite Diamonds Buckyballs

  42. Periodic Table

  43. Metals • Conductors • Lose electrons • Malleable and ductile

  44. Nonmetals • Brittle • Gain electrons • Covalent bonds

  45. Semi-metals or Metalloids

  46. Alkali Metals

  47. Alkaline Earth Metals

  48. Halogens

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