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Chapter 2

Chapter 2. Atoms, Molecules & Ions. Quantum Corral. http://www.almaden.ibm.com/vis/stm/corral.html. Scanning Tunneling Microscope. Scanning Tunneling Microscope. Scanning Tunneling Microscope. http://www.cbu.edu/~mcondren/SeeAtoms.htm. http://mrsec.wisc.edu/. http://mrsec.wisc.edu/.

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Chapter 2

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  1. Chapter 2 Atoms, Molecules & Ions Dr. S. M. Condren

  2. Quantum Corral http://www.almaden.ibm.com/vis/stm/corral.html Dr. S. M. Condren

  3. Scanning Tunneling Microscope Dr. S. M. Condren

  4. Scanning Tunneling Microscope Dr. S. M. Condren

  5. Scanning Tunneling Microscope Dr. S. M. Condren

  6. http://www.cbu.edu/~mcondren/SeeAtoms.htm Dr. S. M. Condren

  7. http://mrsec.wisc.edu/ http://mrsec.wisc.edu/ Developed in collaboration with the Institute for Chemical Education and the Magnetic Microscopy Center University of Minnesota http://www.physics.umn.edu/groups/mmc/ Dr. S. M. Condren

  8. Probe Sample http://www.nsf.gov/mps/dmr/mrsec.htm http://www.nsf.gov/mps/dmr/mrsec.htm Pull Probe Strip Pull Probe Strip Dr. S. M. Condren

  9. Which best represents the poles? (a) (b) (c) North South Dr. S. M. Condren

  10. Atoms & Molecules Atoms • can exist alone or enter into chemical combination • the smallest indivisible particle of an element Molecules • a combination of atoms that has its own characteristic set of properties Dr. S. M. Condren

  11. Law of Constant Composition A chemical compound always contains the same elements in the same proportions by mass. Dr. S. M. Condren

  12. Law of Multiple Proportions • the same elements can be combined to form different compounds by combining the elements in different proportions Dr. S. M. Condren

  13. Dalton’s Atomic Theory Postulates • proposed in 1803 • know at least 2 for first exam Dr. S. M. Condren

  14. Dalton’s Atomic Theory Postulate 1 • An element is composed of tiny particles called atoms. • All atoms of a given element show the same chemical properties. Dr. S. M. Condren

  15. Atoms of different elements have different properties. Dalton’s Atomic Theory Postulate 2 Dr. S. M. Condren

  16. Dalton’s Atomic Theory Postulate 3 • Compounds are formed when atoms of two or more elements combine. • In a given compound, the relative number of atoms of each kind are definite and constant. Dr. S. M. Condren

  17. Dalton’s Atomic Theory Postulate 4 • In an ordinary chemical reaction, no atom of any element disappears or is changed into an atom of another element. • Chemical reactions involve changing the way in which the atoms are joined together. Dr. S. M. Condren

  18. Radioactivity Dr. S. M. Condren

  19. Radioactivity • Alpha – helium-4 nucleus • Beta – high energy electron • Gamma – energy resulting from transitions from one nuclear energy level to another Dr. S. M. Condren

  20. Alpha Radiation • composed of 2 protons and 2 neutrons • thus, helium-4 nucleus • +2 charge • mass of 4 amu • creates element with atomic number 2 lower • Ra226 Rn222 + He4(a) Dr. S. M. Condren

  21. Beta Radiation • composed of a high energy electron which was ejected from the nucleus • “neutron” converted to “proton” • very little mass • -1 charge • creates element with atomic number 1 higher • U239 Np239 + b-1 Dr. S. M. Condren

  22. Gamma Radiation • nucleus has energy levels • energy released from nucleus as the nucleus changes from higher to lower energy levels • no mass • no charge • Ni60* Ni60 + g Dr. S. M. Condren

  23. Cathode Ray Tube Dr. S. M. Condren

  24. Thompson’s Charge/Mass Ratio Dr. S. M. Condren

  25. Millikin’s Oil Drop Dr. S. M. Condren

  26. Rutherford’s Gold Foil Dr. S. M. Condren

  27. Rutherford’s Model of the Atom Dr. S. M. Condren

  28. Rutherford’s Model of the Atom • atom is composed mainly of vacant space • all the positive charge and most of the mass is in a small area called the nucleus • electrons are in the electron cloud surrounding the nucleus Dr. S. M. Condren

  29. Structure of the AtomComposed of: • protons • neutrons • electrons Dr. S. M. Condren

  30. Composed of: protons neutrons electrons protons found in nucleus relative charge of +1 relative mass of 1.0073 amu Structure of the Atom Dr. S. M. Condren

  31. Composed of: protons neutrons electrons neutrons found in nucleus neutral charge relative mass of 1.0087 amu Structure of the Atom Dr. S. M. Condren

  32. Composed of: protons neutrons electrons electrons found in electron cloud relative charge of -1 relative mass of 0.00055 amu Structure of the Atom Dr. S. M. Condren

  33. Size of Nucleus If the nucleus were 1” in diameter, the atom would be 1.5 miles in diameter. Dr. S. M. Condren

  34. Ions • charged single atom • charged cluster of atoms Dr. S. M. Condren

  35. Ions • cations • positive ions • anions • negative ions • ionic compounds • combination of cations and anions • zero net charge Dr. S. M. Condren

  36. Atomic number, Z • the number of protons in the nucleus • the number of electrons in a neutral atom • the integer on the periodic table for each element Dr. S. M. Condren

  37. Isotopes • atoms of the same element which differ in the number of neutrons in the nucleus • designated by mass number Dr. S. M. Condren

  38. Mass Number, A • integer representing the approximate mass of an atom • equal to the sum of the number of protons and neutrons in the nucleus Dr. S. M. Condren

  39. Masses of Atoms Carbon-12 Scale Dr. S. M. Condren

  40. Isotopes of Hydrogen H-1, 1H, protium • 1 proton and no neutrons in nucleus • only isotope of any element containing no neutrons in the nucleus • most common isotope of hydrogen Dr. S. M. Condren

  41. Isotopes of Hydrogen H-2 or D, 2H, deuterium • 1 proton and 1 neutron in nucleus Dr. S. M. Condren

  42. Isotopes of Hydrogen H-3 or T, 3H, tritium • 1 proton and 2 neutrons in nucleus Dr. S. M. Condren

  43. Isotopes of Oxygen O-16 • 8 protons, 8 neutrons, & 8 electrons O-17 • 8 protons, 9 neutrons, & 8 electrons O-18 • 8 protons, 10 neutrons, & 8 electrons Dr. S. M. Condren

  44. The radioactive isotope 14C has how many neutrons? 6, 8, other Dr. S. M. Condren

  45. The identity of an element is determined by the number of which particle? protons, neutrons, electrons Dr. S. M. Condren

  46. Mass Spectrometer Dr. S. M. Condren

  47. Mass Spectra of Neon Dr. S. M. Condren

  48. Measurement of Atomic Masses Mass Spectrometer a simulation is available at http://www.colby.edu/chemistry/ OChem/DEMOS/MassSpec.html Dr. S. M. Condren

  49. Atomic Masses andIsotopic Abundances natural atomic masses = sum[(atomic mass of isotope) *(fractional isotopic abundance)] Dr. S. M. Condren

  50. Example: Chlorine has two isotopes, Cl-35 and Cl-37, which have masses of 34.96885 and 36.96590 amu, respectively. The natural atomic mass of chlorine is 35.453 amu. What are the percent abundances of the two isotopes? let x = fraction Cl-35 y = fraction Cl-37 x + y = 1 y = 1 - x (AW Cl-35)(fraction Cl-35) + (AW Cl-37)(fraction Cl-37) = 35.453 Thus: 34.96885*x + 36.96590*y = 35.453 Dr. S. M. Condren

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