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Chapter 2

Chapter 2. Atoms, Molecules, and Ions. History. Greeks Democritus and Leucippus – atomos (meaning indivisible or uncutable) Aristotle- elements Alchemy English schoolteacher, John Dalton linked the idea of elements with the idea of atoms. 1803-1807. Dalton’s Atomic Theory.

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Chapter 2

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  1. Chapter 2 Atoms, Molecules, and Ions

  2. History Greeks Democritus and Leucippus – atomos (meaning indivisible or uncutable) Aristotle- elements Alchemy English schoolteacher, John Dalton linked the idea of elements with the idea of atoms. 1803-1807

  3. Dalton’s Atomic Theory 1. Elements are made up of atoms 2. Atoms of each element are identical. Atoms of different elements are different. 3. Compounds are formed when atoms combine. Each compound has a specific number and kinds of atom. 4. Chemical reactions are rearrangement of atoms. Atoms are not created or destroyed.

  4. Laws • Conservation of Mass • Law of Definite Proportion- compounds have a constant composition by mass. • They react in specific ratios by mass. • Multiple Proportions- When two elements form more than one compound, the ratios of the masses of the second element that combine with one gram of the first can be reduced to small whole numbers.

  5. What?! • Water has 8 g of oxygen per g of hydrogen. • Hydrogen peroxide has 16 g of oxygen per g of hydrogen. • 16/8 = 2/1 • Small whole number ratios

  6. Experiments to determine what an atom was • J. J. Thomson- used Cathode ray tubes • Thomson’s experiment is generally accepted as the discovery of the electron.

  7. Voltage source Thomson’s Experiment - +

  8. Voltage source Thomson’s Experiment - +

  9. Voltage source Thomson’s Experiment - +

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

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

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

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

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

  15. Voltage source Thomson’s Experiment + - • By adding an electric field

  16. Voltage source Thomson’s Experiment + - • By adding an electric field

  17. Voltage source Thomson’s Experiment + - • By adding an electric field

  18. Voltage source Thomson’s Experiment + - • By adding an electric field

  19. Voltage source Thomson’s Experiment + - • By adding an electric field

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

  21. 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

  22. Radioactivity • Discovered by accident • Bequerel • Three types • alpha- helium nucleus (+2 charge, large mass) • beta- high speed electron • gamma- high energy light

  23. 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

  24. Florescent Screen Lead block Uranium Gold Foil

  25. What he expected

  26. Because

  27. Because, he thought the mass was evenly distributed in the atom

  28. What he got

  29. Atom is mostly empty Small dense, positive piece at center Alpha particles are deflected by it if they get close enough + How he explained it

  30. +

  31. Modern View The atom is mostly empty space Two regions Nucleus- protons and neutrons Electron cloud- region where you have a chance of finding an electron

  32. 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

  33. Symbols A X Z 23 Na 11

  34. Chemical Bonds The forces that hold atoms together Covalent bonding - sharing electrons makes molecules Chemical formula- the number and type of atoms in a molecule C2H6 - 2 carbon atoms, 6 hydrogen atoms, Structural formula shows the connections, but not necessarily the shape.

  35. There are also other model that attempt to show three dimensional shape Ball and stick Space Filling

  36. Ions Atoms or groups of atoms with a charge Cations- positive ions - get by losing electrons(s) Anions- negative ions - get by gaining electron(s) Ionic bonding- held together by the opposite charges Ionic solids are called salts

  37. Ions A polyatomic ion are groups of atoms that have a charge Chemical symbol for ions A ± # X

  38. Periodic Table

  39. Metals Conductors Lose electrons Malleable and ductile

  40. Nonmetals Brittle Gain electrons Covalent bonds

  41. Semi-metals or Metalloids

  42. Alkaline Earth Metals

  43. Alkaline Earth Metals

  44. Halogens

  45. Transition metals

  46. Noble Gases

  47. Inner Transition Metals

  48. +1 +2 -3 -2 -1

  49. More Naming

  50. Naming compounds Two types Ionic - metal and non metal or polyatomics Covalent- we will just learn the rules for 2 non-metals

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