Atoms and their structure

1. Atoms and their structure

2. History of the atom • Original idea Ancient Greece (400 B.C..) • Democritus Greek philosophers

3. History of Atom • Smallest possible piece? • Atoms - not to be cut • Looked at beach • Made of sand

4. Another Greek • Aristotle - Famous philosopher • All substances are made of 4 elements • Fire - Hot • Air - light • Earth - cool, heavy • Water - wet • Blend these in different proportions to get all substances • His ideas were mostly opinion

5. Examples? • Can you think of examples to prove invisible particles exist, even though we can’t see them?

6. Who Was Right? • Greek society was slave based • Beneath Famous to work with hands • did not experiment • Greeks settled disagreements by argument • Aristotle was more famous • He won • His ideas carried through middle ages. • Alchemists tried to change lead to gold

7. Who’s Next? • 1808- John Dalton- England • Teacher- summarized results of his experiments and those of other’s • In Dalton’s Atomic Theory • Combined ideas of elements with that of atoms

8. Dalton’s Atomic Theory • All matter is made of tiny indivisible particles (atoms) Dalton was wrong here • Atoms of the same element are identical • Atoms can’t be subdivided, created, or destroyed • Atoms of different elements combine in whole number ratios to form compounds • Chemical reactions involve the rearrangement of atoms.

9. Fundamental Laws of Chemistry • Dalton used “atoms” to explain the following laws: • Law of Conservation of Mass • Number of reactants = number of products • Law of Definite Proportions • Compounds have a constant composition by mass • Every sample of water is made up of 2 H and 1 O; NaCl = 1 Na and 1 Cl • Does not matter how many crystals of NaCl you have • Law of Multiple Proportions • If two elements make up more than one compound, then the ratio of the elements will always be a whole number ratio. • H2O and H2O2 but not H2.3O0.7

10. Analogy • A bicycle has 2 wheels, a tricycle has three wheels. It’s a 2:3 ratio, a small, whole number ratio • Now it’s your turn…

11. Laws of Multiple and Definete

12. Parts of Atoms • J. J. Thomson - English physicist. 1897 • Made a piece of equipment called a cathode ray tube. • It is a vacuum tube - all the air has been pumped out, gas under low pressure • Why? • Because without the pressure, the particles will flow easier

13. Voltage source Thomson’s Experiment + - Vacuum tube Anode Cathode Metal Disks

14. Voltage source Thomson’s Experiment - +

15. Voltage source Thomson’s Experiment - +

16. Voltage source Thomson’s Experiment - +

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

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

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

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

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

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

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

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

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

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

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

28. Thomson`s Model • Found the electron • Couldn’t find positive (for a while) • Said the atom was like plum pudding • Positive stuff, with the electrons randomly surrounding it • Like watermelon, the seeds are spread throughout and do not contribute to the mass of the fruit

29. Millikan- 1909 • Discovered the charge on the electron • Gave it a unit- Coulomb (C) • 1.602 x 10-19 = q (q stands for charge) • 1/2000 mass of hydrogen http://cwx.prenhall.com/petrucci/medialib/media_portfolio/02.html

30. Rutherford’s experiment • Ernest Rutherford English physicist. (1910) • Believed in the plum pudding model of the atom. • Wanted to see how big they are • Used radioactivity • Alpha particles – He with pos. charge- given off by uranium • Shot them at gold foil which can be made a few atoms thick

31. Florescent Screen Lead block Uranium Gold Foil

32. He Expected • The alpha particles to pass through without changing direction very much • Because the positive charges were spread out evenly. Alone they were not enough to stop the alpha particles

33. What he expected

34. Because

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

36. What he got

37. + How he explained it • Atom is mostly empty • Small dense, positive piece at center • Alpha particles are deflected by it if they get close enough • “It was like shooting a bullet at a piece of tissue paper and have the bullet reflect off the paper back at you”

38. +

39. What Did It Prove? • The atom has a nucleus • Small, dense bundle of positive charge • Nucleus has a small volume compared to the rest of the atom

40. Niels Bohr 1913 suggested that electrons in an atom move in set paths around the nucleus Much like planets orbit around the sun

41. Summarize • Create a table showing the experiment, date and discovery from each of the following: • Millikan, Dalton, Thomson, Rutherford

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

43. Subatomic particles Actual mass (g) Relative mass Name Symbol Charge Electron e- -1 1/1840 9.11 x 10-28 Proton p+ +1 1 1.67 x 10-24 Neutron n0 0 1 1.67 x 10-24

44. Size of an atom • Atoms are small. • Protons and neutrons = nucleus • Nucleus tiny compared to atom • If the atom was the size of a stadium, the nucleus would be the size of a marble. • Radius of the nucleus near 10-15m. • Density near 1014 g/cm • What charge does the nucleus contain?

45. Flinn Mapping the Atom activity

46. Questions • Three compounds containing O and k have 1.22g, 2.44g and 4.89g of K. Show how this data supports the L.M.P. • Compare in terms of location, mass and charge- electrons, proton and neutron • If I change the number of protons in a substance, will it be the same substance?

47. Counting the Pieces • Atomic Number = number of protons • # of protons determines kind of atom • Same as the number of electrons in the neutral atom • Atomic Mass = the number of protons + neutrons (AKA Mass Number) • All the things with mass

48. Symbols • Contain the symbol of the element, the mass number and the atomic number Mass number X Atomic number

49. Symbols • Find the • number of protons • number of neutrons • number of electrons • Atomic number • Mass Number 19 F 9

50. Symbols • Find the • number of protons • number of neutrons • number of electrons • Atomic number • Mass Number 80 Br 35