Chapter 5

1. Chapter 5 Atomic Structure and the Periodic Table

2. Section 5.1Atoms • OBJECTIVES: • Summarize Dalton’s atomic theory.

3. Section 5.1Atoms • OBJECTIVES: • Describe the size of an atom.

4. History of the atom • Not the history of atom, but the idea of the atom. • Original idea Ancient Greece (400 B.C.) • Democritus and Leucippus- Greek philosophers.

5. History of Atom • Smallest possible piece? • Atomos - not to be cut • Looked at beach • Made of sand • Cut sand - smaller sand

6. 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

7. 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 change lead to gold.

8. Who’s Next? • Late 1700’s - John Dalton- England. • Teacher- summarized results of his experiments and those of others. • Dalton’s Atomic Theory • Combined ideas of elements with that of atoms.

9. Dalton’s Atomic Theory • All matter is made of tiny indivisible particles called atoms. • Atoms of the same element are identical, those of different atoms are different. • Atoms of different elements combine in whole number ratios to form compounds. • Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed.

10. Just How Small Is an Atom? • Think of cutting a piece of lead into smaller and smaller pieces • How far can it be cut? • An atom is the smallest particle of an element that retains the properties of that element • Atoms-very small: Fig. 5.2, p. 108 • still observable with proper instruments: Fig. 5.3, page 108

11. Section 5.2Structure of the Nuclear Atom • OBJECTIVES: • Distinguish among protons, electrons, and neutrons in terms of relative mass and charge.

12. Section 5.2Structure of the Nuclear Atom • OBJECTIVES: • Describe the structure of an atom, including the location of the protons, electrons, and neutrons with respect to the nucleus.

13. 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.

14. Voltage source Thomson’s Experiment - + Vacuum tube Metal Disks

15. Voltage source Thomson’s Experiment - +

16. Voltage source Thomson’s Experiment - +

17. Voltage source Thomson’s Experiment - +

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

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

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

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

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

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

29. Other particles • Proton - positively charged pieces 1840 times heavier than the electron – by E. Goldstein • Neutron - no charge but the same mass as a proton – by J. Chadwick • Where are the pieces?

30. Rutherford’s experiment • Ernest Rutherford -English physicist. (1910) • Believed in the plum pudding model of the atom (discussed in Chapter 13). • Wanted to see how big they are. • Used radioactivity. • Alpha particles - positively charged pieces- helium atoms minus electrons • Shot them at gold foil which can be made a few atoms thick.

31. Rutherford’s experiment • When an alpha particle hits a fluorescent screen, it glows. • Here’s what it looked like (page 111)

32. Fluorescent Screen Lead block Uranium Gold Foil

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

34. What he expected

35. Because

36. He thought the mass was evenly distributed in the atom

37. Since he thought the mass was evenly distributed in the atom

38. What he got

39. + 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.

40. +

41. Density and the Atom • Since most of the particles went through, it was mostly empty space. • Because the pieces turned so much, the positive pieces were heavy. • Small volume, big mass, big density. • This small dense positive area is the nucleus.

42. Subatomic particles – p.111 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

43. Section 5.3Distinguishing Between Atoms • OBJECTIVES: • Explain how the atomic number identifies an element.

44. Section 5.3Distinguishing Between Atoms • OBJECTIVES: • Use the atomic number and mass number of an element to find the numbers of protons, electrons, and neutrons.

45. Section 5.3Distinguishing Between Atoms • OBJECTIVES: • Explain how isotopes differ, and why the atomic masses of elements are not whole numbers.

46. Section 5.3Distinguishing Between Atoms • OBJECTIVES: • Calculate the average atomic mass of an element from isotope data.

47. Counting the Pieces • Atomic Number = number of protons in the nucleus • # of protons determines kind of atom (since all protons are alike!) • the same as the number of electrons in the neutral atom. • Mass Number = the number of protons + neutrons. • These account for most of mass

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

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

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