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Chapter 4 Practice Problems Solutions p. 111 15. a. b. c. d. e. f. g. h. 19 B 5 5 16 16 23 23 16. a. 9 protons and 9 electrons b. 20 protons and 20 electrons c. 13 protons and 13 electrons p. 112 17 a. b. c. d. e. 8 16 61 45 125 18. a. 12C 6 b. 19 F9 c. 9Be4 p. 113 19. 16 O8 , 17O8, 18O8. 20. Chromium- 50 has 26 neutrons, chromium – 52 has 28 neutrons, and chromium – 53 has 29 neutrons. p. 116 21. Boron – 11 22. Silicon- 28 must be by far the most abundant. The other two isotopes must be present in very small amounts. p. 117 23. 63.6 amu 24. 79.91 amu Section Assessment 4.1 1. As indivisible and indestructible. 2. By using experimental methods. 3. A scanning tunneling microscope. 4. Answers should include the ideas that all matter is composed of atoms, atoms of different elements differ, and chemical change involves a rearrangement of atoms. 5. Atoms of one element are never changed into atoms of another element as a result of a chemical reaction. 6. 5 x 10-2 nm to 2 x 10-1 nm 7. 1.05 x 10-22 g 63.5 g = ? (6.02 x 1023 atoms) Section Assessment 4.2 8. Protons, neutrons, and electrons. 9. A positively charged nucleus surrounded by electrons, which occupy most of the volume. 10. Proton, positive charge, relative mass = 1, electron, negative charge, relative mass = 1/1840, neutron, no charge, relative mass = 1. 11. Thomson passed an electric current through sealed glass tubes filled with gases. The resulting glowing beam consisted of tiny negatively charged particles moving at high speed. Thomson concluded that electrons must be parts of the atoms of all elements. Millikan determined the charge and mass of the electron. 12. Rutherford expected all the alpha particles to pass straight through with little deflection. He found that most alpha particles passes straight through, but some particles were deflected at very large angles and some even bounced straight back. 13. The great majority of the alpha particles passed straight through the gold foil. 14. Rutherford’s atomic model describes the atom as having a positively charged, dense nucleus that is tiny compared to the atom as a whole. In Thomson’s plum pudding model, electrons were stuck in a chunk of positive charge. Section Assessment 4.3 25. Atoms of different elements contain different numbers of protons. 26. Mass number – atomic number = number of neutrons. 27. They have different mass numbers and different numbers of neutrons. 28. For each isotope, multiply its atomic mass by it % abundance, then add the products. 29. It allows you to compare the properties of the elements. 30. Mass number 194 Pt 78. 31. The atomic mass is the weighted average of the masses of its isotopes. 32. 33. a. Lithium – 6 Lithium – 7 3 protons 3 protons b. Calcium – 42 Calcium – 44 20 protons 20 electrons 22 neutrons 20 protons 20 electrons 24 neutrons c. Selenium – 78 Selenium – 80 34 protons 34 electrons 44 neutrons 34 protons 34 electrons 46 neutrons 3 electrons 3 neutrons 3 electrons 4 neutrons Any two; beryllium (Be), magnesium (Mg), strontium (Sr), barium (Ba), radium (Ra). End of Chapter 4 Assessment 34. The smallest particle of an element that still has the properties of that element. 35. Democritus’ ideas were not helpful in explaining chemical behavior because they lacked experimental support. 36. Dalton would agree with all four-statement because they all fit his atomic theory. 37. The atoms are separated, joined, and rearranged. 38. a. A beam of electrons (cathode rays) is deflected by an electric field toward the positively charged plate. b. The cathode rays were always composted of electrons regardless of the metal used in the electrodes or the gas used in the cathode ray tube. 39. Repel. 40. The mass of the proton and neutron are equals, protons are positively charged and neutrons are neutral. 41. Atoms are neutral: number of protons= number of electrons. Loss of an electron means that the number of protons is greater than the number of electrons, so the remaining particle is positively charged. 42. The electrons were stuck in a lump of positive charge. 43. Rutherford did not expect alpha particles to be deflected over a large angle. 44. Positive. 45. Protons and neutrons. 46. It has equal numbers of protons and electrons. 47. The number of protons in the nucleus. 48. a. b. c. d. e. f. 49. 15 42 13 48 24 82 The atomic number is the number of protons. The mass number is the sum of the protons and neutrons. 50. Atomic Number Mass Number Number Number Symbol of Protons of Neutrons of Element 9 19 9 10 F 14 29 14 15 Si 22 47 22 25 Ti 25 55 25 30 Mn 51. Mass number, atomic masses, number of neutrons, relative abundance. 52. Because of the existence of isotopes. 53. Which isotopes exist, their masses, and their natural percent abundance. 54. Average atomic mass is the arithmetic mean of the isotopes. Weighted average atomic mass considers both the mass and the relative abundance of the isotopes. 55. The atomic mass is the weighted average of the masses of all the isotopes. 56. According to their atomic numbers. 57. Sample answer: The table is set up so that chemical properties recur at regular intervals. 58. Very, very, tiny - but larger than protons and electrons. 59. The nucleus is very small and very dense compared with the atom. 60. 5 protons and 6 neutrons in the nucleus, 5 electrons outside the nucleus. 61. All atoms of the same element are not identical (isotopes.). The atom is not the smallest particle of matter. 62. He used the quantity of charge value and the charge to mass ratio measured by Thompson. 63. They are the same value. 64. The masses of isotopes in a sample of the element are average, based on relative abundance. The result is the element’s atomic mass. 65. 207 amu 66. No, in general he proposed a valid theory in line with the experimental evidence available to him. 67. Atoms are the smallest particle of an element that retains the properties of that element. 68. a. 92.9 % = 8289000/ 8922261 b. 99.89 % = 8912140/ 892261 c. 0.00993 % = 886/ 892261 69. 14 N7, 14.003 amu, 99.63 %, 15N7, 15.000 amu, 0.37 %, average atomic mass = 14.01 amu. 70. They were attracted to a positively charged plate. 71. Atomic number is the same as the number of protons and electrons, mass number minus atomic equals number of neutrons. 72. Because they have identical numbers of protons, they also have identical numbers of electrons; electrons are the subatomic particles that are responsible for chemical behavior. 73. The pattern repeats. 74. a. The nucleus of an atom. b. Very small volume, almost all the mass of the atom, high density, positive charge. c. Electron. 75. Change the metal used as a target and account for differences in deflection patterns. 76. 77. The following are reasonable hypotheses. The space in an individual atom is large relative to the volume of the atom, but very small relative to an object the size of a hand. There are may layers of atoms in a wall or a desk. The space that exists is distributed evenly throughout the solid, similar to the distribution of air pockets in foam insulation. The theory must be modified and then retested. 78. Yes, but answers will vary. 79. In a chemical change, atoms are neither created not destroyed; instead they are rearranged. 80. Because diamond is denser than graphite, pressure could be used to squeeze the carbon atoms closer together. 81. 92.5 % = x 6.941 = y (6.015) + x (7.016) 6.941 = (1-x)(6.015) + x (7.016) 82. 4 x 10-25 g 17(1.67 x 10-24) + 18 (1.67 x 10-24) = 5.845 x 10-23 g - 5.81 x 10-23 g = 3.5 x 10-25 g 83. Pure chemistry involves the accumulation of scientific knowledge for it so own sake; applied chemistry is accumulating knowledge to attain a specific goal. 84. Scientific theory attempts to explain why experiments give certain results. Scientific law describes a natural phenomenon but does not explain it. 85. a. b. c. d. Element Mixture Mixture Mixture 86. 48 g 87. 6.38 x 107 cm3 88. 99.5 g