Chapter 5

1. Chapter 5 Atomic Structure and the Periodic Table Milbank High School

2. Section 5.1Atoms • Learning Target: • I can summarize Dalton’s atomic theory.

3. Section 5.1Atoms • Learning Target: • I can describe the size of an atom.

4. First Ideas • 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

5. 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.

6. 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.

7. 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

8. Section 5.2Structure of the Nuclear Atom • Learning Target: • I can distinguish among protons, electrons, and neutrons in terms of relative mass and charge.

9. Section 5.2Structure of the Nuclear Atom • Learning Target: • I can describe the structure of an atom, including the location of the protons, electrons, and neutrons with respect to the nucleus.

10. 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. • Determined the presence of electrons in atoms

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

12. Voltage source Thomson’s Experiment - +

13. Voltage source Thomson’s Experiment - +

14. Voltage source Thomson’s Experiment - +

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

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

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 beam appear to move from the negative to the positive end

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

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

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 he found that the moving pieces were negative

26. Other particles • Proton - positively charged pieces 1840 times heavier than the electron • Neutron - no charge but the same mass as a proton

27. Rutherford’s experiment • Ernest Rutherford -English physicist. (1910) • Wanted to see how big atoms 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.

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

29. Fluorescent Screen Lead block Uranium Gold Foil

30. 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.

31. + 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.

32. 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.

33. 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

34. Section 5.3Distinguishing Between Atoms • Learning Target: • I can explain how the atomic number identifies an element.

35. Section 5.3Distinguishing Between Atoms • Learning Target: • I can use the atomic number and mass number of an element to find the numbers of protons, electrons, and neutrons.

36. Section 5.3Distinguishing Between Atoms • Learning Target: • I can explain how isotopes differ, and why the atomic masses of elements are not whole numbers.

37. Section 5.3Distinguishing Between Atoms • Learning Target: • I can calculate the average atomic mass of an element from isotope data.

38. 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

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

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

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

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

43. Symbols • if an element has an atomic number of 34 and a mass number of 78 what is the • number of protons • number of neutrons • number of electrons • Complete symbol

44. Symbols • if an element has 91 protons and 140 neutrons what is the • Atomic number • Mass number • number of electrons • Complete symbol

45. Symbols • if an element has 78 electrons and 117 neutrons what is the • Atomic number • Mass number • number of protons • Complete symbol

46. Isotopes • Dalton was wrong. • Atoms of the same element can have different numbers of neutrons. • different mass numbers. • called isotopes.

47. Naming Isotopes • We can also put the mass number after the name of the element. • carbon- 12 • carbon -14 • uranium-235

48. Atomic Mass • How heavy is an atom of oxygen? • There are different kinds of oxygen atoms. • More concerned with average atomic mass. • Based on abundance of each element in nature. • Don’t use grams because the numbers would be too small.

49. Measuring Atomic Mass • Unit is the Atomic Mass Unit (amu) • One twelfth the mass of a carbon-12 atom. • Each isotope has its own atomic mass, thus we determine the average from percent abundance.

50. Calculating averages • Multiply the atomic mass of each isotope by it’s abundance (expressed as a decimal), then add the results. • Sample 5-5, p.120