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Chapter 2

Atoms, Molecules & Ions. Chapter 2. HST. Quantum Corral. http://www.almaden.ibm.com/vis/stm/corral.html. Scanning Tunneling Microscope. Scanning Tunneling Microscope. Scanning Tunneling Microscope. http://mrsec.wisc.edu/. http://mrsec.wisc.edu/. Developed in collaboration with the

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Chapter 2

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

  2. Quantum Corral http://www.almaden.ibm.com/vis/stm/corral.html

  3. Scanning Tunneling Microscope

  4. Scanning Tunneling Microscope

  5. Scanning Tunneling Microscope

  6. 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/

  7. Probe Sample http://www.nsf.gov/mps/dmr/mrsec.htm http://www.nsf.gov/mps/dmr/mrsec.htm Pull Probe Strip Pull Probe Strip

  8. Which best represents the poles? (a) (b) (c) North South

  9. 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

  10. Law of Constant Composition A chemical compound always contains the same elements in the same proportions by mass.

  11. Law of Multiple Proportions the same elements can be combined to form different compounds by combining the elements in different proportions

  12. Dalton’s Atomic Theory Postulates proposed in 1803 know at least 2 for first exam

  13. 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.

  14. Dalton’s Atomic Theory Postulate 2 Atoms of different elements have different properties.

  15. 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.

  16. 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.

  17. Radioactivity

  18. Radioactivity Alpha – helium-4 nucleus Beta – high energy electron Gamma – energy resulting from transitions from one nuclear energy level to another

  19. 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)

  20. 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

  21. 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

  22. Cathode Ray Tube

  23. Thompson’s Charge/Mass Ratio

  24. Millikin’s Oil Drop

  25. Rutherford’s Gold Foil

  26. Rutherford’s Model of the Atom

  27. 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

  28. Structure of the AtomComposed of: protons neutrons electrons

  29. Structure of the Atom Composed of: protons neutrons electrons protons found in nucleus relative charge of +1 relative mass of 1.0073 amu

  30. Structure of the Atom Composed of: protons neutrons electrons neutrons found in nucleus neutral charge relative mass of 1.0087 amu

  31. Structure of the Atom Composed of: protons neutrons electrons electrons found in electron cloud relative charge of -1 relative mass of 0.00055 amu

  32. Size of Nucleus If the nucleus were 1” in diameter, the atom would be 1.5 miles in diameter.

  33. Ions charged single atom charged cluster of atoms

  34. Ions cations positive ions anions negative ions ionic compounds combination of cations and anions zero net charge

  35. 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

  36. Isotopes atoms of the same element which differ in the number of neutrons in the nucleus designated by mass number

  37. 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

  38. Masses of Atoms Carbon-12 Scale

  39. 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

  40. Isotopes of Hydrogen H-2 or D, 2H, deuterium 1 proton and 1 neutron in nucleus

  41. Isotopes of Hydrogen H-3 or T, 3H, tritium 1 proton and 2 neutrons in nucleus

  42. 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

  43. The radioactive isotope 14C has how many neutrons? 6, 8, other

  44. The identity of an element is determined by the number of which particle? protons, neutrons, electrons

  45. Mass Spectrometer

  46. Mass Spectra of Neon

  47. Measurement of Atomic Masses Mass Spectrometer a simulation is available at http://www.colby.edu/chemistry/ OChem/DEMOS/MassSpec.html

  48. Atomic Masses andIsotopic Abundances natural atomic masses = sum[(atomic mass of isotope) *(fractional isotopic abundance)]

  49. 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

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