Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Biochemistry wikipedia , lookup
Light-dependent reactions wikipedia , lookup
Mass spectrometry wikipedia , lookup
Isotopic labeling wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
Oxidative phosphorylation wikipedia , lookup
CHAPTER TWO ATOMS, MOLECULES, AND IONS Questions 15. a. Atoms have mass and are neither destroyed nor created by chemical reactions. Therefore, mass is neither created nor destroyed by chemical reactions. Mass is conserved. b. The composition of a substance depends on the number and kinds of atoms that form it. c. Compounds of the same elements differ only in the numbers of atoms of the elements forming them, i.e., NO, N2 O, NO2 . 16. Some elements exist as molecular substances. That is, hydrogen normally exists as H2 molecules, not single hydrogen atoms. The same is true for N2 , O2 , F2 , Cl2 , etc. 17. Deflection of cathode rays by magnetic and electric fields led to the conclusion that they were negatively charged. The cathode ray was produced at the negative electrode and repelled by the negative pole of the applied electric field. 18. J. J. Thomson discovered electrons. Henri Becquerel discovered radioactivity. Lord Rutherford proposed the nuclear model of the atom. Dalton's original model proposed that atoms were indivisible particles (that is, atoms had no internal structure). Thomson and Becquerel discovered subatomic particles, and Rutherford's model attempted to describe the internal structure of the atom composed of these subatomic particles. In addition, the existence of isotopes, atoms of the same element but with different mass, had to be included in the model. 19. The proton and neutron have similar mass with the mass of the neutron slightly larger than that of the proton. Each of these particles has a mass approximately 1800 times greater than that of an electron. The combination of the protons and the neutrons in the nucleus makes up the bulk of the mass of an atom, but the electrons make the greatest contribution to the chemical properties of the atom. 20. If the plum pudding model were correct (a diffuse positive charge with electrons scattered throughout), then alpha particles should have traveled through the thin foil with very minor deflections in their path. This was not the case as a few of the alpha particles were deflected at very large angles. Rutherford reasoned that the large deflections of these alpha particles could be caused only by a center of concentrated positive charge that contains most of the atom’s mass (the nuclear model of the atom). 21. The atomic number of an element is equal to the number of protons in the nucleus of an atom of that element. The mass number is the sum of the number of protons plus neutrons in the nucleus. The 18 CHAPTER 2 ATOMS, MOLECULES, AND IONS 19 atomic mass is the actual mass of a particular isotope (including electrons). As we will see in Chapter Three, the average mass of an atom is taken from a measurement made on a large number of atoms. The average atomic mass value is listed in the periodic table. 22. A family is a set of elements in the same vertical column. A family is also called a group. A period is a set of elements in the same horizontal row. 23. A compound will always contain the same numbers (and types) of atoms. A given amount of hydrogen will react only with a specific amount of oxygen. Any excess oxygen will remain unreacted. 24. The halogens have a high affinity for electrons, and one important way they react is to form anions of the type X-. The alkali metals tend to give up electrons easily and in most of their compounds exist as M+ cations. Note: These two very reactive groups are only one electron away (in the periodic table) from the least reactive family of elements, the noble gases. Exercises Development of the Atomic Theory 25. a. The composition of a substance depends on the numbers of atoms of each element making up the compound (i.e., on the formula of the compound) and not on the composition of the mixture from which it was formed. b. Avogadro’s hypothesis implies that volume ratios are equal to molecule ratios at constant temperature and pressure. H2 (g) + Cl2 (g) ÷ 2 HCl(g). From the balanced equation (2 molecules of HCl are produced per molecule of H2 or Cl2 reacted), the volume of HCl produced will be twice the volume of H2 (or Cl2 ) reacted. 26. 27. From Avogadro’s hypothesis, volume ratios are equal to molecule ratios at constant temperature and pressure. Therefore, we can write a balanced equation using the volume data, Cl2 + 3 F2 ÷ 2 X. Two molecules of X contain 6 atoms of F and two atoms of Cl. The formula of X is ClF3 for a balanced equation. =1.000; = 1.999; = 2.999 The masses of fluorine are simple ratios of whole numbers to each other, 1:2:3. 28. Hydrazine: 1.44 × 10-1 g H/g N; Ammonia: 2.16 × 10-1 g H/g N Hydrogen azide: 2.40 × 10-2 g H/g N Let's try all of the ratios: = 6.00; = 9.00; = 1.50 = 20 CHAPTER 2 ATOMS, MOLECULES, AND IONS All the masses of hydrogen in these three compounds can be expressed as simple whole number ratios. The g H/g N in hydrazine, ammonia, and hydrogen azide are in the ratios 6:9:1. 29. To get the atomic mass of H to be 1.00, we divide the mass of hydrogen that reacts with 1.00 g of oxygen by 0.126, i.e., = 1.00. To get Na, Mg and O on the same scale, we do the same division. Na: = 22.8; Mg: Relative Value Accepted Value = 11.9; O: = 7.94 H O Na Mg 1.00 7.94 22.8 11.9 1.008 16.00 22.99 24.31 The atomic masses of O and Mg are incorrect; the atomic masses of H and Na are close to the values in the periodic table. Something must be wrong about the assumed formulas of the compounds. It turns out the correct formulas are H2 O, Na2 O, and MgO. The smaller discrepancies result from the error in the atomic mass of H. 30. If the formula is InO, then one atomic mass of In would combine with one atomic mass of O, or: , A = atomic mass of In = 76.54 If the formula is In2 O3 , then two times the atomic mass of In will combine with three times the atomic mass of O, or: , A = atomic mass of In = 114.8 The latter number is the atomic mass of In used in the modern periodic table. The Nature of the Atom 31. Density of hydrogen nucleus (contains one proton only): Vnucleus = d= (3.14) (5 × 10-14 cm)3 = 5 × 10-40 cm3 = 3 × 1015 g/cm3 Density of H-atom (contains one proton and one electron): Vatom = (3.14) (1 × 10-8 cm)3 = 4 × 10-24 cm3 CHAPTER 2 ATOMS, MOLECULES, AND IONS = 0.4 g/cm3 d= 32. 21 Since electrons move about the nucleus at an average distance of about 1 × 10-8 cm, then the diameter of an atom is about 2 × 10-8 cm. Let's set up a ratio: , Solving: diameter of model = 2 × 105 mm = 200 m 33. 5.93 × 10-18 C × 34. First, divide all charges by the smallest quantity, 6.40 × 10-13. = 37 negative (electron) charges on the oil drop = 4.00; = 12.00; = 6.00 Since all charges are whole number multiples of 6.40 × 10-13 zirkombs, then the charge on one electron could be 6.40 × 10-13 zirkombs. However, 6.40 × 10-13 zirkombs could be the charge of two electrons (or three electrons, etc.). All one can conclude is that the charge of an electron is 6.40 × 10-13 zirkombs or an integer fraction of 6.40 × 10-13 zirkombs. 35. sodium - Na; beryllium - Be; manganese - Mn; chromium - Cr; uranium - U 36. fluorine - F; chlorine - Cl; bromine - Br; sulfur - S; oxygen - O; phosphorus - P 37. Sn - tin; Pt - platinum; Co - cobalt; Ni - nickel; Mg - magnesium; Ba - barium; K - potassium 38. As - arsenic; I - iodine; Xe - xenon; He - helium; C - carbon; Si - silicon 39. The noble gases are He, Ne, Ar, Kr, Xe, and Rn (helium, neon, argon, krypton, xenon, and radon). Radon has only radioactive isotopes. In the periodic table, the whole number enclosed in parentheses is the mass number of the longest-lived isotope of the element. 40. promethium (Pm) and technetium (Tc) 41. a. Eight; Li to Ne b. Eight; Na to Ar 42. c. Eighteen; K to Kr a. Six; Be, Mg, Ca, Sr, Ba, Ra d. Five; N, P, As, Sb, Bi b. Five; O, S, Se, Te, Po c. Four; Ni, Pd, Pt, Uun d. Six; He, Ne, Ar, Kr, Xe, Rn 43. a. Pu: 94 protons, 238 - 94 = 144 neutrons b. Cu: 29 protons, 65 - 29 = 36 neutrons 22 44. CHAPTER 2 ATOMS, MOLECULES, AND IONS c. Cr: 24 protons, 28 neutrons d. He: 2 protons, 2 neutrons e. Co: 27 protons, 33 neutrons f. a. Br: 35 protons, 79 - 35 = 44 neutrons. Since the charge of the atom is neutral, the number Cr: 24 protons, 30 neutrons of protons = the number of electrons = 35. b. c. Pu: 94 protons, 145 neutrons, 94 electrons d. Cs: 55 protons, 78 neutrons, 55 electrons e. f. 45. Br: 35 protons, 46 neutrons, 35 electrons H: 1 proton, 2 neutrons, 1 electron Fe: 26 protons, 30 neutrons, 26 electrons a. Element #5 is boron. B b. Z = 7; A = 7 + 8 = 15; c. Z = 17; A = 17 + 18 = 35; e. Z = 6; A = 14; 46. C d. A = 92 + 143 = 235; f. Z = 15; A = 31; a. Element 8 is oxygen. A = mass number = 9 + 8 = 17; b. Chlorine is element 17. Cl d. Z = 26; A = 26 + 31 + 57; f. Lithium is element 3. 47. Cl U P O c. Cobalt is element 27. Fe N e. Iodine is element 53. Co I Li Atomic number = 63 (Eu); Charge = +63 - 60 = +3; Mass number = 63 + 88 = 151; Symbol: Eu3+ Atomic number = 50 (Sn); Mass number = 50 + 68 = 118; Net charge = +50 - 48 = +2; The symbol is Sn2+ . 48. 49. Atomic number = 16 (S); Charge = +16 - 18 = -2; Mass number = 16 + 18 = 34; Symbol: S2- Atomic number = 16 (S); Charge = +16 - 18 = -2; Mass number = 16 + 16 = 32; Symbol: S2- CHAPTER 2 ATOMS, MOLECULES, AND IONS 23 Number of protons in nucleus Number of neutrons in nucleus Number of electrons Net charge As3+ 33 42 30 3+ Te2- 52 76 54 2- S 16 16 16 0 Tl+ 81 123 80 1+ Pt 78 117 78 0 Symbol 50. Number of protons in nucleus Number of neutrons in nucleus Number of electrons Net charge 92 146 92 0 Ca2+ 20 20 18 2+ V3+ 23 28 20 3+ Y 39 50 39 0 Br- 35 44 36 1- P3- 15 16 18 3- Symbol U 51. Metals: Mg, Ti, Au, Bi, Ge, Eu, Am. Nonmetals: Si, B, At, Rn, Br. 52. Si, Ge, B, At. The elements at the boundary between the metals and the nonmetals are: B, Si, Ge, As, Sb, Te, Po, At. Aluminum has mostly properties of metals. 53. a and d. A group is a vertical column of elements in the periodic table. Elements in the same family 24 CHAPTER 2 ATOMS, MOLECULES, AND IONS (group) have similar chemical properties. 54. a. transition metals c. alkali metals e. halogens 55. Carbon is a nonmetal. Silicon and germanium are metalloids. Tin and lead are metals. Thus, metallic character increases as one goes down a family in the periodic table. 56. The metallic character decreases from left to right. 57. Metals lose electrons to form cations, and nonmetals gain electrons to form anions. Group 1A, 2A and 3A metals form stable +1,+2 and +3 charged cations, respectively. Group 5A, 6A and 7A nonmetals form -3, -2 and -1 charged anions, respectively. 58. b. alkaline earth metals d. noble gases a. Lose 1 e- to form Na+ . b. Lose 2 e- to form Sr2+. c. Lose 2 e- to form Ba2+ . d. Gain 1 e- to form I-. e. Lose 3 e- to form Al3+ . f. a. Lose 2 e- to form Ra2+. b. Lose 3 e- to form In3+ . c. Gain 3 e- to form P3-. d. Gain 2 e- to form Te2-. e. Gain 1 e- to form Br-. f. Gain 2 e- to form S2-. Lose 1 e- to form Rb+ . Nomenclature 59. 60. 61. a. sodium chloride b. rubidium oxide c. calcium sulfide d. aluminum iodide a. mercury(I) oxide b. iron(III) bromide c. cobalt(II) sulfide d. titanium(IV) chloride a. chromium(VI) oxide b. chromium(III) oxide d. sodium hydride e. calcium bromide f. 62. c. aluminum oxide zinc chloride (Zinc only forms +2 ions so no Roman numerals are needed for zinc compounds.) a. cesium fluoride b. lithium nitride c. silver sulfide (Silver only forms +1 ions so no Roman numerals are needed.) 63. 64. d. manganese(IV) oxide e. titanium(IV) oxide a. potassium perchlorate b. calcium phosphate c. aluminum sulfate d. lead(II) nitrate a. barium sulfite b. sodium nitrite c. potassium permanganate d. potassium dichromate f. strontium phosphide CHAPTER 2 65. 66. 67. 68. 69. 70. 25 a. nitrogen triiodide b. sulfur difluoride c. phosphorus trichloride d. dinitrogen tetrafluoride a. dinitrogen tetroxide b. iodine trichloride c. sulfur dioxide d. diphosphorus pentasulfide a. copper(I) iodide b. copper(II) iodide d. sodium carbonate e. sodium hydrogen carbonate or sodium bicarbonate f. tetrasulfur tetranitride g. sulfur hexafluoride i. barium chromate j. c. cobalt(II) iodide h. sodium hypochlorite ammonium nitrate a. acetic acid b. ammonium nitrite c. cobalt(III) sulfide d. iodine monochloride e. lead(II) phosphate f. potassium iodate g. sulfuric acid h. strontium nitride i. aluminum sulfite j. k. sodium chromate l. hypochlorous acid tin(IV) oxide a. CsBr b. BaSO4 c. NH4 Cl d. ClO e. SiCl4 f. g. BeO h. MgF2 ClF3 a. SF2 b. SF6 c. NaH2 PO4 d. Li3 N e. Cr2 (CO3 )3 f. SnF2 g. NH4 C2 H3 O2 h. NH4 HSO4 i. Co(NO3 )3 k. KClO3 l. NaH j. 71. ATOMS, MOLECULES, AND IONS Hg2 Cl2 ; Mercury(I) exists as Hg2 2+ ions. a. Na2 O b. Na2 O2 c. KCN d. Cu(NO3 )2 e. SeBr4 f. PbS g. PbS2 h. CuCl i. GaAs (Predict Ga3+ and As3- ions.) j. CdSe (Cadmium only forms +2 charged ions in compounds.) k. ZnS (Zinc only forms +2 charged ions in compounds.) l. 72. HNO2 m. P2 O5 a. (NH4 )2HPO4 b. Hg2S c. SiO2 d. Na2 SO3 e. Al(HSO4 )3 f. NCl3 g. HBr h. HBrO2 i. HBrO4 j. KHS k. CaI2 l. CsClO4 26 CHAPTER 2 ATOMS, MOLECULES, AND IONS Additional Exercises 73. Yes, 1.0 g H would react with 37.0 g 37Cl and 1.0 g H would react with 35.0 g 35Cl. No, the mass ratio of H/Cl would always be 1 g H/37 g Cl for 37 Cl and 1 g H/35 g Cl for 35 Cl. As long as we had pure 37 Cl or pure 35 Cl, the above ratios will always hold. If we have a mixture (such as the natural abundance of chlorine), the ratio will also be constant as long as the composition of the mixture of the two isotopes does not change. 74. : 43 protons and 55 neutrons; : 43 protons and 56 neutrons Tc is in the same family as Mn. We would expect Tc to have properties similar to Mn. permanganate: MnO4 -; pertechnetate: TcO4 -; ammonium pertechnetate: NH4TcO4 75. 76. a. nitric acid, HNO3 b. perchloric acid, HClO4 d. sulfuric acid, H2 SO4 e. phosphoric acid, H3PO4 c. acetic acid, HC2 H3 O2 a. Fe2+ : 26 protons (Fe is element 26.); protons - electrons = charge, 26 -2 = 24 electrons; FeO is the formula since the oxide ion has a -2 charge. b. Fe3+ : 26 protons; 23 electrons; Fe2O3 c. Ba2+ : 56 protons; 54 electrons; BaO d. Cs+ : 55 protons; 54 electrons; Cs2O e. S2-: 16 protons; 18 electrons; Al2S3 f. P3-: 15 protons; 18 electrons; AlP g. Br-: 35 protons; 36 electrons; AlBr3 h. N3-: 7 protons; 10 electrons; AlN 77. a. Pb(C2 H3 O2 )2 : lead(II) acetate b. CuSO4 : copper(II) sulfate c. CaO: calcium oxide d. MgSO4 : magnesium sulfate e. Mg(OH)2 : magnesium hydroxide f. CaSO4 : calcium sulfate g. N2 O: dinitrogen monoxide or nitrous oxide 78. a. This is element 52, tellurium. Te forms stable -2 charged ions (like other oxygen family members). b. Rubidium. Rb, element 37, forms stable +1 charged ions. c. Argon. Ar is element 18. d. Astatine. At is element 85. CHAPTER 2 79. ATOMS, MOLECULES, AND IONS 27 A chemical formula gives the actual number and kind of atoms in a compound. In all cases, 12 hydrogen atoms are present. For example: 4 molecules H3 PO4 × = 12 atoms H 80. From the XBr2 formula, the charge on element X is +2. Therefore, the element has 88 protons, which identifies it as radium, Ra. 230 - 88 = 142 neutrons 81. a. Ca2+ and N3-: Ca3 N2 , calcium nitride b. K+ and O2-: K2 O, potassium oxide c. Rb+ and F-: RbF, rubidium fluoride d. Mg2+ and S2-: MgS, magnesium sulfide e. Ba2+ and I-: BaI2, barium iodide f. Al3+ and Se2-: Al2Se3, aluminum selenide g. Cs+ and P3-: Cs3 P, cesium phosphide h. In3+ and Br-: InBr3 , indium(III) bromide. In also forms In+ ions, but one would predict In3+ ions from its position in the periodic table. 82. These compounds are similar to phosphate (PO4 3-) compounds. Na3 AsO4 contains Na+ ions and AsO4 3ions. The name would be sodium arsenate. H3 AsO4 is analogous to phosphoric acid, H 3 P O 4 . H3 AsO4 would be arsenic acid. Mg3 (SbO4 )2 contains Mg2+ ions and SbO4 3- ions, and t h e n a me would be magnesium antimonate. Challenge Problems 83. Copper(Cu), silver (Ag) and gold(Au) make up the coinage metals. 84. Avogadro proposed that equal volumes of gases (at constant temperature and pressure) contain equal numbers of molecules. In terms of balanced equations, Avogadro’s hypothesis implies that volume ratios will be identical to molecule ratios. Assuming one molecule of octane reacting, then 1 molecule of Cx Hy produces 8 molecules of CO2 and 9 molecules of H2 O. Cx Hy + O2 ÷ 8 CO2 + 9 H2 O. Since all the carbon in octane ends up as carbon in CO2, then octane contains 8 atoms of C. Similarly, all hydrogen in octane ends up as hydrogen in H2 O, so one molecule of octane contains 9 × 2 = 18 atoms of H. Octane formula = C8 H18 and the ratio of C:H = 8:18 or 4:9. 85. Compound I: ; Compound II: The ratio of the masses of R that combine with 1.00 g Q is: = 2.99 . 3 As expected from the law of multiple proportions, this ratio is a small whole number. Since Compound I contains three times the mass of R per gram of Q as compared to Compound II (RQ), then the formula of Compound I should be R3 Q. 28 CHAPTER 2 ATOMS, MOLECULES, AND IONS 86. The alchemists were incorrect. The solid residue must have come from the flask. 87. a. Both compounds have C2 H6 O as the formula. Because they have the same formula, their mass percent composition will be identical. However, these are different compounds with different properties since the atoms are bonded together differently. These compounds are called isomers of each other. b. When wood burns, most of the solid material in wood is converted to gases, which escape. The gases produced are most likely CO2 and H2 O. c. The atom is not an indivisible particle, but is instead composed of other smaller particles, e.g., electrons, neutrons, protons. d. The two hydride samples contain different isotopes of either hydrogen and/or lithium. Although the compounds are composed of different isotopes, their properties are similar because different isotopes of the same element have similar properties (except, of course, their mass).