Atoms Molecules and Ions

Atoms, Molecules, and Ions 1. The first people to attempt to explain why chemical changes occur were A) alchemists B) metallurgists C) physicians D) physicists E) the Greeks ANS: E 2. The Greeks proposed that matter consisted of four fundamental substances: A) fire, earth, water, air B) fire, metal, water, air C) earth, metal, water, air D) atoms, fire, water, air E) atoms, metal, fire, air ANS: A 3. The first chemist to perform truly quantitative experiments was A) Paracelsus B) Boyle C) Priestly D) Bauer E) Lavoisier ANS: B 4. The scientist who discovered the law of conservation of mass and is also called the father of modern chemistry is A) Proust B) Boyle C) Priestly D) Bauer E) Lavoisier ANS: E KEY: Chemistry | general chemistry | general concepts | matter | Law of Conservation of Mass 5. Which of the following pairs of compounds can be used to illustrate the law of multiple proportions? A) NH4 and NH4Cl B) ZnO2 and ZnCl2 C) H2O and HCl D) NO and NO2 E) CH4 and CO2 ANS: D | atomic theory of matter | Dalton's atomic theory 6. Which of the following pairs can be used to illustrate the law of multiple proportions? A) SO and SO2 B) CO and CaCO3 C) H2O and C12H22O11 D) H2SO4 and H2S E) KCl and KClO2 ANS: A | atomic theory of matter 7. According to the law of multiple proportions: A) If the same two elements form two different compounds, they do so in the same ratio. B) It is not possible for the same two elements to form more than one compound. C) The ratio of the masses of the elements in a compound is always the same. D) The total mass after a chemical change is the same as before the change. E) None of these. ANS: E | atomic theory of matter | Dalton's atomic theory 8. A sample of chemical X is found to contain 5.0 grams of oxygen, 10.0 grams of carbon, and 20.0 grams of nitrogen. The law of definite proportion would predict that a 70 gram sample of chemical X should contain how many grams of carbon? A) 5.0 grams B) 7.0 grams C) 10. grams D) 15 grams E) 20 grams ANS: E | atomic theory of matter | Dalton's atomic theory 9. Consider the following two compounds: H2O and H2O2 . According to the law of multiple proportions, the ratio of hydrogen atoms per gram of oxygen in H2O to hydrogen atoms per gram of oxygen in H2O2 is A) 1:1 B) 2:1 C) 1:2 D) 2:2 E) 4:1 ANS: B | atomic theory of matter | Dalton's atomic theory 10. Which of the following statements from Dalton's atomic theory is no longer true, according to modern atomic theory? A) Elements are made up of tiny particles called atoms. B) Atoms are not created or destroyed in chemical reactions. C) All atoms of a given element are identical. D) Atoms are indivisible in chemical reactions. E) All of these statements are true according to modern atomic theory. ANS: C | atomic theory of matter | Dalton's atomic theory 11. How many of the following postulates of Dalton's atomic theory are still scientifically accepted? I. All atoms of the same element are identical. II. Compounds are combinations of different atoms. III. A chemical reaction changes the way atoms are grouped together. IV. Atoms are indestructible. A) 0 B) 1 C) 2 D) 3 E) 4 ANS: C | atomic theory of matter | Dalton's atomic theory 12. The chemist credited for inventing a set of symbols for writing elements and a system for writing the formulas of compounds (and for discovering selenium, silicon, and thorium) is A) Boyle B) Lavoisier C) Priestly D) Berzelius E) Dalton ANS: D | chemical substance | chemical formula 13. Avogadro's hypothesis states that: A) Each atom of oxygen is 16 times more massive than an atom of hydrogen. B) A given compound always contains exactly the same proportion of elements by mass. C) When two elements form a series of compounds, the ratios of masses that combine with 1 gram of the first element can always be reduced to small whole numbers. D) At the same temperature and pressure, equal volumes of different gases contain an equal number of particles. E) Mass is neither created nor destroyed in a chemical reaction. ANS: D 14. The first scientist to show that atoms emit any negative particles was A) J. J. Thomson B) Lord Kelvin C) Ernest Rutherford D) William Thomson E) John Dalton ANS: A REF: 2.4 | atomic theory of matter | structure of the atom | discovery of electron 15. Many classic experiments have given us indirect evidence of the nature of the atom. Which of the experiments listed below did not give the results described? A) The Rutherford experiment proved the Thomson "plum-pudding" model of the atom to be essentially correct. B) The Rutherford experiment was useful in determining the nuclear charge on the atom. C) Millikan's oil-drop experiment showed that the charge on any particle was a simple multiple of the charge on the electron. D) The electric discharge tube proved that electrons have a negative charge. E) All of the above experiments gave the results described. ANS: A REF: 2.4 | atomic theory of matter | structure of the atom 16. The scientist whose alpha-particle scattering experiment led him to conclude that the nucleus of an atom contains a dense center of positive charge is A) J. J. Thomson B) Lord Kelvin C) Ernest Rutherford D) William Thomson E) John Dalton ANS: C REF: 2.4 | atomic theory of matter | structure of the atom | nuclear model of atom 17. Alpha particles beamed at thin metal foil may A) pass directly through without changing direction B) be slightly diverted by attraction to electrons C) be reflected by direct contact with nuclei D) A and C E) A, B, and C ANS: E REF: 2.4 | atomic theory of matter | structure of the atom | nuclear model of atom 18. Which one of the following statements about atomic structure is false? A) An atom is mostly empty space. B) Almost all of the mass of the atom is concentrated in the nucleus. C) The protons and neutrons in the nucleus are very tightly packed. D) The number of protons and neutrons is always the same in the neutral atom. E) All of the above statements (A-D) are true. ANS: D REF: 2.4 | atomic theory of matter | structure of the atom | nuclear model of atom 19. If the Thomson model of the atom had been correct, Rutherford would have observed: A) Alpha particles going through the foil with little or no deflection. B) Alpha particles greatly deflected by the metal foil. C) Alpha particles bouncing off the foil. D) Positive particles formed in the foil. E) None of the above observations is consistent with the Thomson model of the atom. ANS: A REF: 2.4 | atomic theory of matter | structure of the atom | nuclear model of atom 20. Which statement is not correct? A) The mass of an alpha particle is 7300 times that of the electron. B) An alpha particle has a 2+ charge. C) Three types of radioactive emission are gamma rays, beta rays, and alpha particles. D) A gamma ray is high-energy light. E) There are only three types of radioactivity known to scientists today. ANS: E REF: 2.4 | atomic theory of matter 21. Rutherford's experiment was important because it showed that: A) Radioactive elements give off alpha particles. B) Gold foil can be made to be only a few atoms thick. C) A zinc sulfide screen scintillates when struck by a charged particle. D) The mass of the atom is uniformly distributed throughout the atom. E) An atom is mostly empty space. ANS: E REF: 2.4 | atomic theory of matter | structure of the atom | nuclear model of atom 22. Bromine exists naturally as a mixture of bromine-79 and bromine-81 isotopes. An atom of bromine-79 contains A) 35 protons, 44 neutrons, 35 electrons B) 34 protons and 35 electrons, only C) 44 protons, 44 electrons, and 35 neutrons D) 35 protons, 79 neutrons, and 35 electrons E) 79 protons, 79 electrons, and 35 neutrons ANS: A REF: 2.5 | atomic theory of matter | nuclear structure 23. Which of the following atomic symbols is incorrect? A) B) C) D) E) ANS: E REF: 2.5 | atomic theory of matter | structure of the atom 24. The element rhenium (Re) exists as two stable isotopes and 18 unstable isotopes. Rhenium-185 has in its nucleus A) 75 protons, 75 neutrons B) 75 protons, 130 neutrons C) 130 protons, 75 neutrons D) 75 protons, 110 neutrons E) not enough information ANS: D REF: 2.5 | atomic theory of matter | isotope 25. Which among the following represent a set of isotopes? Atomic nuclei containing: I. 20 protons and 20 neutrons II. 21 protons and 19 neutrons III. 22 neutrons and 18 protons IV. 20 protons and 22 neutrons V. 21 protons and 20 neutrons A) I, II, III B) III, IV C) I, V D) I, IV and II, V E) No isotopes are indicated. ANS: D REF: 2.5 | atomic theory of matter | isotope 26. By knowing the number of protons a neutral atom has, you should be able to determine A) the number of neutrons in the neutral atom B) the number of electrons in the neutral atom C) the name of the atom D) two of the above E) none of the above ANS: D REF: 2.5 | atomic theory of matter | nuclear structure 27. Which of the following statements are true of uranium-238? I. Its chemical properties will be exactly like those of uranium-235. II. Its mass will be slightly different from that of an atom of uranium-235. III. It will contain a different number of protons than an atom of uranium-235. IV. It is more plentiful in nature than uranium-235. A) III, IV B) I, II, III C) I, II, IV D) II, III, IV E) all of these ANS: C REF: 2.5 | atomic theory of matter | isotope 28. An isotope, X, of a particular element has an atomic number of 15 and a mass number of 31. Therefore: A) X is an isotope of phosphorus. B) X has 16 neutrons per atom. C) X has an atomic mass of 30.973. D) A and B. E) A, B, and C. ANS: D REF: 2.5 | atomic theory of matter | isotope 29. Which of the following statements is true? A) Ions are formed by adding or removing protons or electrons. B) Scientists believe that solids are mostly open space. C) Heating water with a Bunsen burner results in a 2:1 mixture of hydrogen and oxygen gases. D) At least two of the above statements (A-C) are true. E) All of the statements (A-C) are false. ANS: B REF: 2.5 30. The number of neutrons in an atom is the same for all neutral atoms of that element. ANS: F REF: 2.5 | atomic theory of matter | isotope 31. The number of electrons in an atom is the same for all neutral atoms of that element. ANS: T REF: 2.5 | atomic theory of matter | nuclear structure 32. has A) 20 protons, 20 neutrons, and 18 electrons B) 22 protons, 20 neutrons, and 20 electrons C) 20 protons, 22 neutrons, and 18 electrons D) 22 protons, 18 neutrons, and 18 electrons E) 20 protons, 20 neutrons, and 22 electrons ANS: A REF: 2.6 | atomic theory of matter | isotope 33. Which of the following statements is (are) true? A) and have the same number of neutrons. B) and are isotopes of each other because their mass numbers are the same. C) has the same number of electrons as . D) A and B E) A and C ANS: E REF: 2.6 | atomic theory of matter | isotope 34. A species with 12 protons and 10 electrons is A) Ne2+ B) Ti2+ C) Mg2+ D) Mg E) Ne2– ANS: C REF: 2.6 | atomic theory of matter | nuclear structure 35. The numbers of protons, neutrons, and electrons in K+ are: A) 20 p, 19 n, 19 e B) 20 p, 19 n, 20 e C) 19 p, 20 n, 20 e D) 19 p, 20 n, 19 e E) 19 p, 20 n, 18 e ANS: E REF: 2.6 | atomic theory of matter | nuclear structure 36. An ion is formed A) By either adding or subtracting protons from the atom. B) By either adding or subtracting electrons from the atom C) By either adding or subtracting neutrons from the atom. D) All of the above are true. E) Two of the above are true. ANS: B REF: 2.6 | chemical substance | chemical formula | ionic substance 37. The formula of water, H2O, suggests: A) There is twice as much mass of hydrogen as oxygen in each molecule. B) There are two hydrogen atoms and one oxygen atom per water molecule. C) There is twice as much mass of oxygen as hydrogen in each molecule. D) There are two oxygen atoms and one hydrogen atom per water molecule. E) None of these. ANS: B REF: 2.6 | chemical substance | chemical formula | molecular substance 38. All of the following are true except: A) Ions are formed by adding electrons to a neutral atom. B) Ions are formed by changing the number of protons in an atom's nucleus. C) Ions are formed by removing electrons from a neutral atom. D) An ion has a positive or negative charge. E) Metals tend to form positive ions. ANS: B REF: 2.6 | chemical substance | chemical formula | ionic substance 39. Which of the following are incorrectly paired? A) K, alkali metal B) Ba, alkaline earth metal C) O, halogen D) Ne, noble gas E) Ni, transition metal ANS: C REF: 2.7 | periodic table | group 40. Which of the following are incorrectly paired? A) Sr, alkaline earth metal B) Ta, transition metal C) F, halogen D) H, noble gas E) Ru, transition metal ANS: D REF: 2.7 | periodic table | group 41. Which of the following are incorrectly paired? A) Phosphorus, Pr B) Palladium, Pd C) Platinum, Pt D) Lead, Pb E) Potassium, K ANS: A REF: 2.7 | periodic table 42. Which of the following are incorrectly paired? A) Copper, Cu B) Carbon, C C) Cobalt, Co D) Calcium, Ca E) Cesium, Ce ANS: E REF: 2.7 | periodic table 43. Which of the following are incorrectly paired? A) Antimony, Sb B) Silicon, Si C) Silver, Ag D) Argon, Ar E) Astatine, As ANS: E REF: 2.7 | periodic table 44. All of the following are characteristics of metals except: A) good conductors of heat B) malleable C) ductile D) often lustrous E) tend to gain electrons in chemical reactions ANS: E REF: 2.7 | periodic table | metal 45. All of the following are characteristics of nonmetals except: A) poor conductors of electricity B) often bond to each other by forming covalent bonds C) tend to form negative ions in chemical reactions with metals D) appear in the upper left-hand corner of the periodic table E) do not have a shiny (lustrous) appearance ANS: D REF: 2.7 | periodic table | nonmetal 46. Which of the following has 61 neutrons, 47 protons, and 46 electrons? A) Pm B) Ag+ C) Pd– D) Cd+ E) Ag ANS: B REF: 2.7 | periodic table 47. How many protons and electrons does the most stable ion for oxygen have? # protons # electrons A) 10 p 8 e B) 8 p 6 e C) 6 p 8 e D) 8 p 8 e E) 8 p 10 e ANS: E REF: 2.8 | periodic table | group 48. You are given a compound with the formula MCl2, in which M is a metal. You are told that the metal ion has 26 electrons. What is the identity of the metal? A) Fe B) Al C) Zn D) Co E) Ni ANS: E REF: 2.7 | chemical substance | chemical formula | ionic substance 49. Which of the following names is incorrect? A) cobalt(II) chloride B) magnesium oxide C) aluminum(III) oxide D) diphosphorus pentoxide E) All of the above names are correct. ANS: C REF: 2.8 | chemical substance | nomenclature of simple compound 50. Which of the following pairs is incorrect? A) iodine trichloride, ICl3 B) phosphorus pentoxide, P2O5 C) ammonia, NH3 D) sulfur hexafluoride, SF6 E) All of the above pairs are correct. ANS: B REF: 2.8 | chemical substance | nomenclature of simple compound | binary molecular compound 51. The correct name for LiCl is A) lithium monochloride B) lithium(I) chloride C) monolithium chloride D) lithium chloride E) monolithium monochloride ANS: D REF: 2.8 | chemical substance | nomenclature of simple compound | ionic compound 52. How many oxygen atoms are there in one formula unit of Ca3(PO4)2? A) 2 B) 4 C) 6 D) 8 E) none of these ANS: D REF: 2.8 | chemical substance | chemical formula | ionic substance 53. How many oxygen atoms are there in 4 formula units of Al2(CO3)3? A) 9 B) 24 C) 36 D) 13 E) 39 ANS: C REF: 2.8 | chemical substance | chemical formula | ionic substance 54. The correct name for FeO is A) iron oxide B) iron(II) oxide C) iron(III) oxide D) iron monoxide E) iron(I) oxide ANS: B REF: 2.8 | chemical substance | nomenclature of simple compound | ionic compound 55. The correct name for Ca2+ is A) calcium B) calcium(II) ion C) calcium ion D) calcium(I) ion E) monocalcium ion ANS: C REF: 2.8 | chemical substance | chemical formula | ionic substance 56. The correct name for V3+ is A) vanadide B) vanadite ion C) vanadium(III) ion D) vanadium(V) ion E) trivanadium ion ANS: C REF: 2.8 | chemical substance | chemical formula | ionic substance 57. The correct name for P3– is A) phosphide ion B) phosphorus ion C) phosphorus(III) ion D) phospho(III) ion E) phosphite ANS: A REF: 2.8 | chemical substance | chemical formula | ionic substance 58. What is the subscript of barium in the formula of barium sulfate? A) 1 B) 2 C) 3 D) 4 E) 0 ANS: A REF: 2.8 | chemical substance | chemical formula | ionic substance 59. The formula for calcium bisulfate is A) Ca(SO4)2 B) CaS2 C) Ca(HSO4)2 D) Ca2HSO4 E) Ca2S ANS: C REF: 2.8 | chemical substance | nomenclature of simple compound | ionic compound 60. The formula for sodium dihydrogen phosphate is A) NaH2PO4 B) Na(HPO4)2 C) NaHPO4 D) Na2HPO4 E) Na2H2PO4 ANS: A REF: 2.8 | chemical substance | nomenclature of simple compound | ionic compound 61. Which of the following is incorrectly named? A) Pb(NO3)2, lead(II) nitrate B) NH4ClO4, ammonium perchlorate C) PO43–, phosphate ion D) Mg(OH)2, magnesium hydroxide E) NO3–, nitrite ion ANS: E REF: 2.8 | chemical substance | nomenclature of simple compound | ionic compound 62. Which of the following is incorrectly named? A) SO32–, sulfite ion B) S2O32–, thiosulfate ion C) PO43–, phosphate ion D) ClO3–, chlorite ion E) CN–, cyanide ion ANS: D REF: 2.8 | chemical substance | nomenclature of simple compound | ionic compound 63. All of the following are in aqueous solution. Which is incorrectly named? A) H2SO4, sulfuric acid B) H2CO3, carbonic acid C) H3PO4, phosphoric acid D) HCN, cyanic acid E) HCl, hydrochloric acid ANS: D REF: 2.8 | chemical substance | nomenclature of simple compound | acid 64. All of the following are in aqueous solution. Which is incorrectly named? A) HC2H3O2, acetic acid B) HBr, bromic acid C) H2SO3, sulfurous acid D) HNO2, nitrous acid E) HClO3, chloric acid ANS: B REF: 2.8 | chemical substance | nomenclature of simple compound | acid 65. Which of the following pairs is incorrect? A) NH4Br, ammonium bromide B) K2CO3, potassium carbonate C) BaPO4, barium phosphate D) CuCl, copper(I) chloride E) MnO2, manganese(IV) oxide ANS: C REF: 2.8 | chemical substance | nomenclature of simple compound | ionic compound 66. Which of the following name(s) is(are) correct? 1. sulfide, S2– 2. ammonium chloride, NH4Cl 3. acetic acid, HC2H3O2 4. barium oxide, BaO A) all B) none C) 1, 2 D) 3, 4 E) 1, 3, 4 ANS: A REF: 2.8 | chemical substance | nomenclature of simple compound 67. Which metals form cations with varying positive charges? A) transition metals B) Group 1 metals C) Group 2 metals D) Group 3 metals E) metalloids ANS: A REF: 2.8 | chemical substance | chemical formula | ionic substance 68. Three samples of a solid substance composed of elements A and Z were prepared. The first contained 4.31 g A and 7.70 g Z. The second sample was 35.9% A and 64.1% Z. It was observed that 0.718 g A reacted with Z to form 2.00 g of the third sample. Show that these data illustrate the law of definite composition. ANS: Sample (1): ratio of masses (Z/A) = 7.70/4.13 = 1.785 Sample (2): ratio of masses (Z/A) = 64.1/35.9 = 1.785 Sample (3): ratio of masses (Z/A) = (2.00-0.718)/0.718 = 1.785 These three samples thus illustrate that a given compound always contains the same proportion of elements by mass. See Sec. 2.2 of Zumdahl, Chemistry. | atomic theory of matter | Dalton's atomic theory 69. Explain how Dalton’s atomic theory accounts for: a) the law of conservation of mass b) the law of definite composition c) the law of multiple proportion ANS: (a) Chemical reactions involve only reorganization of the atoms. (b) A given compound always has the same relative numbers and types of atoms. (c) Since, according to Dalton, atoms of a given element are identical and a given compound always has the same relative numbers and types of atoms, the observation of different mass ratio combinations of the same elements to give different compounds supports the law of multiple proportion. See Sec. 2.3 of Zumdahl, Chemistry. | atomic theory of matter | Dalton's atomic theory 70. Complete the following table. Symbol # Protons # Neutrons # Electrons Net Charge 206Pb 31 38 3+ 52 75 54 Mn2+ 30 2+ ANS: Symbol # Protons # Neutrons # Electrons Net Charge 206Pb 82 124 82 0 Ga3+ 31 38 28 3+ Te2– 52 75 54 2- Mn2+ 25 29 23 2+ REF: 2.5 | atomic theory of matter | nuclear structure 71. Complete the following table. Symbol 69Ga3+ Number of protons 34 Number of neutrons 46 Number of electrons Atomic number Mass number Net charge 2– ANS: Symbol 69Ga3+ 80Se2– Number of protons 31 34 Number of neutrons 38 46 Number of electrons 28 36 Atomic number 31 34 Mass number 69 80 Net charge +3 2– REF: 2.5 | atomic theory of matter | nuclear structure 72. Arsenopyrite is a mineral containing As, Fe, and S. Classify each element as metal, nonmetal, or metalloid. ANS: As = metalloid, Fe = metal, S = nonmetal REF: 2.7 | periodic table 73. Write the symbol for each of the following elements. a) silver _____________ b) calcium _____________ c) iodine _____________ d) copper _____________ e) phosphorus _____________ ANS: a) Ag, b) Ca, c) I, d) Cu, e) P REF: 2.7 | periodic table 74. Write the names of the following compounds: a) FeSO4 ________________ b) NaC2H3O2 ________________ c) KNO2 ________________ d) Ca(OH)2 ________________ e) NiCO3 ________________ ANS: a) iron(II) sulfate b) sodium acetate c) potassium nitrite d) calcium hydroxide e) nickel(II) carbonate REF: 2.8 | chemical substance | nomenclature of simple compound | ionic compound 75. Write the chemical formulas for the following compounds or ions. a) nitrate ion _________ b) aluminum oxide _________ c) ammonium ion _________ d) perchloric acid _________ e) copper(II) bromide _________ ANS: a) NO3– b) Al2O3 c) NH4+ d) HClO4 e) CuBr2 REF: 2.8 | chemical substance | chemical formula | ionic substance 76. How many atoms (total) are there in one formula unit of Ca3(PO4)2? ANS: 13 REF: 2.8 | chemical substance | chemical formula | ionic substance Name the following compounds: 77. Al2(SO4)3 ANS: aluminum sulfate REF: 2.8 | chemical substance | nomenclature of simple compound | ionic compound 78. NH4NO3 ANS: ammonium nitrate REF: 2.8 | chemical substance | nomenclature of simple compound | ionic compound 79. NaH ANS: sodium hydride REF: 2.8 | chemical substance | nomenclature of simple compound | ionic compound 80. K2Cr2O7 ANS: potassium dichromate REF: 2.8 | chemical substance | nomenclature of simple compound | ionic compound 81. CCl4 ANS: carbon tetrachloride REF: 2.8 | chemical substance | nomenclature of simple compound | binary molecular compound 82. AgCl ANS: silver chloride REF: 2.8 | chemical substance | nomenclature of simple compound | ionic compound 83. CaSO4 ANS: calcium sulfate REF: 2.8 | chemical substance | nomenclature of simple compound | ionic compound 84. HNO2 ANS: nitrous acid REF: 2.8 | chemical substance | nomenclature of simple compound | acid 85. N2O3 ANS: dinitrogen trioxide REF: 2.8 | chemical substance | nomenclature of simple compound | binary molecular compound 86. SnI2 ANS: tin(II) iodide REF: 2.8 | chemical substance | nomenclature of simple compound | ionic compound Write the formula for: 87. sodium thiosulfate ANS: Na2S2O3 REF: 2.8 | chemical substance | chemical formula | ionic substance 88. iron(III) oxide ANS: Fe2O3 REF: 2.8 | chemical substance | chemical formula | ionic substance 89. dichlorine heptoxide ANS: Cl2O7 REF: 2.8 | chemical substance | chemical formula | molecular substance 90. cobalt(II) chloride ANS: CoCl2 REF: 2.8 | chemical substance | chemical formula | ionic substance 91. aluminum hydroxide ANS: Al(OH)3 REF: 2.8 | chemical substance | chemical formula | ionic substance 92. sulfurous acid ANS: H2SO3 REF: 2.8 | chemical substance | nomenclature of simple compound | acid 93. nitric acid ANS: HNO3 REF: 2.8 | chemical substance | nomenclature of simple compound | acid 94. phosphoric acid ANS: H3PO4 REF: 2.8 | chemical substance | nomenclature of simple compound | acid 95. acetic acid ANS: CH3COOH REF: 2.8 | chemical substance | nomenclature of simple compound | acid 96. phosphorus trichloride ANS: PCl3 REF: 2.8 | chemical substance | nomenclature of simple compound | binary molecular compound 97. Which of these statements is a consequence (follows from) the Law of Definite Proportion? A) All samples of chlorine contain 35Cl and 37Cl in the same (definite) ratio. B) The mass of oxygen that is combined with a fixed mass of nitrogen in each of the binary nitrogen oxides can be expressed as a ratio of small whole numbers. C) The atomic masses of all of the elements in the periodic table have fixed values. D) The % lead by mass in the compound galena is the same for all pure samples obtained from any source. E) None of these is correct ANS: D | atomic theory of matter | Dalton's atomic theory 98. Which of these statements is a consequence (follows from) the Law of Multiple Proportions? A) All samples of chlorine contain 35Cl and 37Cl in the same (definite) ratio. B) The mass of oxygen that is combined with a fixed mass of nitrogen in each of the binary nitrogen oxides can be expressed as a ratio of small whole numbers. C) The atomic masses of all of the elements in the periodic table have fixed values. D) The % lead by mass in the compound galena is the same for all pure samples obtained from any source. E) None of these is correct ANS: B | atomic theory of matter | Dalton's atomic theory 99. Which of the following elements does NOT have a symbol taken from a LATIN name for the element or one of its compounds? A) iron D) potassium B) copper E) titanium C) sodium ANS: E REF: 2.7 | periodic table 100. Which of the following statements is FALSE? A) sulfur does not conduct electricity D) silicon is a metalloid B) gold is malleable E) hydrogen is a non-metal C) germanium is a metal ANS: C REF: 2.7 | periodic table | 101. Which of the following ions is NOT likely to form from the appropriate atom? A) C4+ D) Ti4+ B) As3- E) Na+ C) Mg2+ ANS: A REF: 2.8 | periodic table | group 102. How many protons, neutrons and electrons, in that order are present in the anion formed by one atom of 125I? A) 53, 74, 54 D) 53, 72, 54 B) 52, 72, 53 E) 54, 74, 54 C) 54, 72, 53 ANS: D REF: 2.8 | atomic theory of matter | isotope | periodic table 103. How many protons, neutrons and electrons, in that order are present in the anion formed by one atom of 79Se? A) 34, 34, 45 D) 34, 45, 36 B) 34, 45, 34 E) 36, 45, 36 C) 32, 45, 34 ANS: D REF: 2.8 | atomic theory of matter | isotope | periodic table 104. Which statement is INCORRECT? A) An atom of 60Zn has an equal number of protons and neutrons B) An atom of 50Mn has an equal number of electrons and neutrons C) An atom of 18O has an equal number of protons and neutrons D) An atom of 41K has an equal number of protons and electrons E) An atom of 238U contains 146 neutrons. ANS: C REF: 2.5 | atomic theory of matter | isotope | 105. Which of the following atoms, isotopes or ions contains 23 protons, 18 electrons and 27 neutrons? A) 45Co5+ D) 41Kr5- B) 50Kr E) 50V5- C) 50V5+ ANS: C REF: 2.8 | atomic theory of matter | isotope | periodic table 106. Which of the following compounds is incorrectly named? A) Mg(OH)2 is magnesium dihydroxide D) K3PO4 is potassium phosphate B) CaO is calcium oxide E) MgSO3 is magnesium sulfite C) NH4NO3 is ammonium nitrate ANS: A REF: 2.8 | chemical substance | nomenclature of simple compound | ionic compound Chapter 2: Atoms, Molecules, and Ions 1. The scientist who determined the magnitude of the electric charge of the electron was A) John Dalton D) Henry Moseley B) Robert Millikan E) J. Burdge C) J. J. Thomson Ans:  B 2. When J. J. Thomson discovered the electron, what physical property of the electron did he measure? A) its charge, e D) its mass, m B) its charge-to-mass ratio, e/m E) its atomic number, Z C) its temperature, T Ans:  B 3. What name is given to the concept that different samples of a given compound always contain the same elements in the same mass ratio? A) Ration Law D) Law of Definite Proportions B) Law of Equality E) 2nd Law of thermodynamics C) 1st Law of Thermodynamics Ans:  D 4. Which field of study made a big contribution toward understanding the composition of the atom? A) Electricity D) Electrochemistry B) Radiation E) Quantum Mechanics C) Solution Chemistry Ans:  B 5. Which of the following is a type of radioactive radiation which has no charge and are unaffected by external electric or magnetic fields? A) ? rays B) ? rays C) ? rays D) ? rays E) ? rays Ans:  C 6. Which of the following is a type of radioactive radiation that consists of positively charged particles and is deflected away from the positively charged plate? A) ? rays B) ? rays C) ? rays D) ? rays E) ? rays Ans:  A 7. Which of the following is a type of radioactive radiation that consists of electrons and is deflected away from the negatively charged plate? A) ? rays B) ? rays C) ? rays D) ? rays E) ? rays Ans:  B 8. Which of these scientists developed the nuclear model of the atom? A) John Dalton D) Henry Moseley B) Robert Millikan E) Ernest Rutherford C) J. J. Thomson Ans:  E 9. Rutherford's experiment with alpha particle scattering by gold foil established that A) protons are not evenly distributed throughout an atom. B) electrons have a negative charge. C) electrons have a positive charge. D) atoms are made of protons, neutrons, and electrons. E) protons are 1840 times heavier than electrons. Ans:  A 10. J. J. Thomson studied cathode ray particles (electrons) and was able to measure the mass/charge ratio. His results showed that A) the mass/charge ratio varied as the cathode material was changed. B) the charge was always a whole-number multiple of some minimum charge. C) matter included particles much smaller than the atom. D) atoms contained dense areas of positive charge. E) atoms are largely empty space. Ans:  B 11. Who is credited with measuring the mass/charge ratio of the electron? A) Dalton B) Chadwick C) Thomson D) Millikan E) Rutherford Ans:  C 12. Who is credited with first measuring the charge of the electron? A) Dalton B) Gay-Lussac C) Thomson D) Millikan E) Rutherford Ans:  D 13. Millikan's oil-drop experiment A) established the charge on an electron. B) showed that all oil drops carried the same charge. C) provided support for the nuclear model of the atom. D) suggested that some oil drops carried fractional numbers of electrons. E) suggested the presence of a neutral particle in the atom. Ans:  A 14. Who is credited with discovering the atomic nucleus? A) Dalton B) Gay-Lussac C) Thomson D) Chadwick E) Rutherford Ans:  E 15. Rutherford bombarded gold foil with alpha (?) particles and found that a small percentage of the particles were deflected. Which of the following was not accounted for by the model he proposed for the structure of atoms? A) the small size of the nucleus B) the charge on the nucleus C) the total mass of the atom D) the existence of protons E) the presence of electrons outside the nucleus Ans:  C 16. Which one of the following statements about atoms and subatomic particles is correct? A) Rutherford discovered the atomic nucleus by bombarding gold foil with electrons. B) The proton and the neutron have identical masses. C) The neutron's mass is equal to that of a proton plus an electron. D) A neutral atom contains equal numbers of protons and electrons. E) An atomic nucleus contains equal numbers of protons and neutrons. Ans:  D 17. Who discovered the subatomic particle having a neutral charge called neutron? A) Millikan B) Dalton C) Chadwick D) Rutherford E) Thomson Ans:  C 18. What term is used to represent the number of protons in the nucleus of each atom of an element and is equal to the number of electrons outside the nucleus? A) Isotope number D) Atomic number B) Mass number E) Atomic mass units C) Mass-to-charge ratio Ans:  D 19. What term is used to represent the total number of neutrons and protons in the nucleus of each atom of an element? A) Isotope number D) Atomic number B) Mass number E) Atomic mass units C) Mass-to-charge ratio Ans:  B 20. Bromine is the only nonmetal that is a liquid at room temperature. Consider the isotope bromine-81, . Select the combination which lists the correct atomic number, neutron number, and mass number, respectively. A) 35, 46, 81 B) 35, 81, 46 C) 81, 46, 35 D) 46, 81, 35 E) 35, 81, 116 Ans:  A 21. Atoms X, Y, Z, and R have the following nuclear compositions: Which two are isotopes? A) X & Y B) X & R C) Y & R D) Z & R E) X & Z Ans:  E 22. Atoms of the same element with different mass numbers are called A) ions. B) neutrons. C) allotropes. D) chemical families. E) isotopes. Ans:  E 23. How many neutrons are there in an atom of lead whose mass number is 208? A) 82 B) 126 C) 208 D) 290 E) None of the above Ans:  B 24. An atom of the isotope sulfur-31 consists of how many protons, neutrons, and electrons? (p = proton, n = neutron, e = electron) A) 15 p, 16 n, 15 e D) 32 p, 31 n, 32 e B) 16 p, 15 n, 16 e E) 16 p, 16 n, 15 e C) 16 p, 31 n, 16 e Ans:  B 25. Give the number of protons (p), electrons (e), and neutrons (n) in one atom of chlorine-37. A) 37 p, 37 e, 17 n D) 37 p, 17 e, 20 n B) 17 p, 17 e, 37 n E) 17 p, 37 e, 17 n C) 17 p, 17 e, 20 n Ans:  C 26. Two isotopes of an element differ only in their A) symbol. D) number of protons. B) atomic number. E) number of electrons. C) atomic mass. Ans:  C 27. A magnesium ion, Mg2+, has A) 12 protons and 13 electrons. D) 24 protons and 22 electrons. B) 24 protons and 26 electrons. E) 12 protons and 14 electrons. C) 12 protons and 10 electrons. Ans:  C 28. An aluminum ion, Al3+, has: A) 13 protons and 13 electrons D) 13 protons and 10 electrons B) 27 protons and 24 electrons E) 10 protons and 13 electrons C) 16 protons and 13 electrons Ans:  D 29. An oxide ion, O2–, has: A) 8 protons and 10 electrons D) 8 protons and 7 electrons B) 10 protons and 8 electrons E) 10 protons and 7 electrons C) 8 protons and 9 electrons Ans:  A 30. A sulfide ion, S2–, has: A) 16 protons and 16 electrons D) 16 protons and 18 electrons B) 32 protons and 16 electrons E) 32 protons and 18 electrons C) 16 protons and 14 electrons Ans:  D 31. How many protons and electrons are present in one Br– ion? A) 35 p, 35 e D) 35 p, 36 e B) 80 p, 81 e E) 80 p, 34 e C) 35 p, 34 e Ans:  D 32. The elements in a column of the periodic table are known as A) metalloids. B) a period. C) noble gases. D) a group. E) nonmetals. Ans:  D 33. Which of these materials are usually poor conductors of heat and electricity? A) metals D) alkaline earth metals B) metalloids E) alkali metals C) nonmetals Ans:  C 34. Which of these elements is most likely to be a good conductor of electricity? A) N B) S C) He D) Cl E) Fe Ans:  E 35. Which of the following elements are the least reactive? A) alkali metals D) alkaline earth metals B) noble gases E) metalloids C) halogens Ans:  B 36. Which of the following is a non-metal? A) lithium, Li, Z = 3 D) bismuth, Bi, Z = 83 B) bromine, Br, Z = 35 E) sodium, Na, Z = 11 C) mercury, Hg, Z = 80 Ans:  B 37. Which of the following is a metal? A) nitrogen, N, Z = 7 D) thallium, Tl, Z = 81 B) phosphorus, P, Z = 15 E) silicon, Si, Z = 14 C) arsenic, Z = 33 Ans:  D 38. Which of the following is a metalloid? A) carbon, C, Z = 6 D) iridium, Z = 77 B) sulfur, S, Z = 16 E) bromine, Br, Z = 35 C) germanium, Ge, Z = 32 Ans:  C 39. A row of the periodic table is called a A) group B) period C) isotopic mixture D) family E) subshell Ans:  B 40. Silicon, which makes up about 25% of Earth's crust by mass, is used widely in the modern electronics industry. It has three naturally occurring isotopes, 28Si, 29Si, and 30Si. Calculate the atomic mass of silicon. Isotope Isotopic Mass (amu) Abundance % 28Si 27.976927 92.23 29Si 28.976495 4.67 30Si 29.973770 3.10 A) 29.2252 amu D) 28.0855 amu B) 28.9757 amu E) 27.9801 amu C) 28.7260 amu Ans:  D 41. Lithium forms compounds which are used in dry cells and storage batteries and in high-temperature lubricants. It has two naturally occurring isotopes, 6Li (isotopic mass = 6.015121 amu) and 7Li (isotopic mass = 7.016003 amu). Lithium has an atomic mass of 6.9409 amu. What is the percent abundance of lithium-6? A) 92.50% B) 86.66% C) 46.16% D) 7.503% E) 6.080% Ans:  D 42. What is the name used to define a mass which is exactly equal to 1/12 the mass of one carbon-12 atom? A) Isotope number D) Atomic number B) Mass number E) Atomic mass units C) Mass-to-charge ratio Ans:  E 43. Which of the following cannot exist as a homonuclear diatomic molecule? A) hydrogen B) phosphorus C) fluorine D) nitrogen E) oxygen Ans:  B 44. Which is the correct definition of a diatomic molecule? A) A molecule which contains two or more of the same atoms B) A molecule which contains two or more different atoms C) A molecule which contains two identical atoms D) A molecule which contains two different atoms E) c and d Ans:  E 45. Which is the correct definition of a polyatomic molecule? A) A molecule which contains two or more of the same atoms B) A molecule which contains two or more different atoms C) a and b D) A molecule which contains two identical atoms E) A molecule which contains two different atoms Ans:  C 46. Which is the correct definition of a heteronuclear diatomic molecule? A) A molecule which contains two or more of the same atoms B) A molecule which contains two or more different atoms C) a and b D) A molecule which contains two identical atoms E) A molecule which contains two different atoms Ans:  E 47. What represents the exact number of atoms of each element in a molecule? A) Chemical formula D) Molecular formula B) Compound E) Atomic formula C) Constitutional formula Ans:  D 48. Which of the following are allotropes? A) diamond and graphite D) hydrogen and oxygen B) hydrogen and deuterium E) None of the above C) bromine and chlorine Ans:  A 49. Which of these elements is chemically similar to magnesium? A) sulfur B) calcium C) iron D) nickel E) potassium Ans:  B 50. Which of these elements is chemically similar to oxygen? A) sulfur B) calcium C) iron D) nickel E) potassium Ans:  A 51. Which of these elements is chemically similar to potassium? A) calcium B) arsenic C) phosphorus D) cerium E) cesium Ans:  E 52. Which, if any, of the following elements do not occur in the major classes of organic compounds? A) H B) C C) N D) O E) All the above elements occur in the major classes of organic compounds. Ans:  E 53. What name is given to a class of compounds that generally do not contain carbon? A) Acarbonic compounds D) Inorganic compounds B) Carbonic compounds E) Aldehyde compounds C) Organic compounds Ans:  D 54. Which of the following is the empirical formula for hexane, C6H14? A) C12H28 B) C6H14 C) C3H7 D) CH2.3 E) C0.43H Ans:  C 55. Which of the following is a molecular formula for CH? A) C2H6 B) C3H9 C) C4H10 D) C6H6 E) None of the answers are correct. Ans:  D 56. What is the name of PCl3? A) phosphorus chloride D) trichlorophosphid B) phosphoric chloride E) phosphorus trichloride C) phosphorus trichlorate Ans:  E 57. The compound, P4S10, is used in the manufacture of safety matches. What is its name? A) phosphorus sulfide D) tetraphosphorus decasulfide B) phosphoric sulfide E) phosphorus sulfite C) phosphorus decasulfide Ans:  D 58. Diiodine pentaoxide is used as an oxidizing agent that converts carbon monoxide to carbon dioxide. What is its chemical formula? A) I2O5 B) IO5 C) 2IO5 D) I5O2 E) (IO5)2 Ans:  A 59. What is the name of P4Se3? A) phosphorus selenide D) phosphoric selenide B) phosphorus triselenide E) tetraphosphorus triselenide C) tetraphosphorus selenide Ans:  E 60. What is the name of ClO-? A) hypochlorite B) chlorate C) chlorite D) perchlorate E) perchlorite Ans:  A 61. What is the formula for the permanganate ion? A) MnO2- B) MnO4- C) MgO42- D) Mn2O7- E) MgO22- Ans:  B 62. Tetrasulfur dinitride decomposes explosively when heated. What is its formula? A) S2N4 B) S4N2 C) 4SN2 D) S4N E) S2N Ans:  B 63. An anion is defined as A) a charged atom or group of atoms with a net negative charge. B) a stable atom. C) a group of stable atoms. D) an atom or group of atoms with a net positive charge. E) neutral. Ans:  A 64. Which one of these species is an ion? A) B3+ B) NaCl C) He D) 14C E) None of the above Ans:  A 65. Which of these pairs of elements would be most likely to form an ionic compound? A) P and Br B) Cu and K C) C and O D) O and Zn E) Al and Rb Ans:  D 66. Which pair of elements would be most likely to form an ionic compound? A) P and Br B) Zn and K C) F and Al D) C and S E) Al and Rb Ans:  C 67. What is the formula for the ionic compound formed by calcium ions and nitrate ions? A) Ca3N2 B) Ca(NO3)2 C) Ca2NO3 D) Ca2NO2 E) CaNO3 Ans:  B 68. What is the formula for the ionic compound formed by calcium and selenium? A) CaSe B) Ca2Se C) CaSe2 D) Ca3Se E) CaSe3 Ans:  A 69. Which is the correct formula for copper (II) phosphate? A) Cu2PO4 B) Cu3(PO4)2 C) Cu2PO3 D) Cu(PO4)2 E) Cu(PO3)2 Ans:  B 70. The chemical name for ClO3– is “chlorate ion”. What is the common name for HClO3? A) hydrochloric acid D) chlorous acid B) chloroform E) chloric acid C) hydrogen trioxychloride Ans:  E 71. The formula for magnesium sulfate is A) MnS B) MgS C) MnSO3 D) MgSO4 E) MnSO4 Ans:  D 72. The formula for sodium sulfide is A) NaS B) K2S C) NaS2 D) Na2S E) SeS Ans:  D 73. The chemical formula for iron (II) nitrate is A) Fe2(NO3)3 B) Ir(NO2)2 C) Fe2N3 D) Fe(NO3)2 E) Fe(NO2)2 Ans:  D 74. Which one of the following formulas of ionic compounds is the least likely to be correct? A) NH4Cl B) Ba(OH)2 C) Na2SO4 D) Ca2NO3 E) Cu(CN)2 Ans:  D 75. What is the formula for lead (II) oxide? A) PbO B) PbO2 C) Pb2O D) PbO4 E) Pb2O3 Ans:  A 76. Potassium permanganate is a strong oxidizer that reacts explosively with easily oxidized materials. What is its formula? A) KMnO3 B) KMnO4 C) K2MnO4 D) K(MnO4)2 E) K2Mn2O7 Ans:  B 77. Ferric oxide is used as a pigment in metal polishing. Which of the following is its formula? A) FeO B) Fe2O C) FeO3 D) Fe2O5 E) Fe2O3 Ans:  E 78. What is the name of Mn(CO3)2? A) manganese carbide D) magnesium (II) carbonate B) magnesium (IV) carbonate E) manganese (IV) carbonate C) manganese (II) carbonate Ans:  E 79. Iron (III) chloride hexahydrate is used as a coagulant for sewage and industrial wastes. What is its formula? A) Fe(Cl·6H2O)3 D) Fe3Cl(H2O)6 B) Fe3Cl·6H2O E) FeCl3·6H2O C) FeCl3(H2O)6 Ans:  E 80. Which of the following is the oxoanion of bromine called the bromate ion? A) BrO3- B) BrO32- C) BrO42- D) BrO2- E) BrO- Ans:  A 81. The mass of a neutron is equal to the mass of a proton plus the mass of an electron. Ans:  False 82. All neutral atoms of tin have 50 protons and 50 electrons. Ans:  True 83. Copper (Cu) is a transition metal. Ans:  True 84. Lead (Pb) is a main-group element. Ans:  True 85. Ionic compounds may carry a net positive or negative charge. Ans:  False 86. When an alkali metal combines with a non-metal, a covalent bond is normally formed. Ans:  False 87. The empirical formula of C6H6 is CH. Ans:  True 88. Almost all the mass of an atom is concentrated in the nucleus. Ans:  True 89. When a beam of alpha particles passes between two electrically charged plates, the beam is deflected toward the positive plate. Ans:  False 90. J. J. Thomson suggested the name “radioactivity” to describe the spontaneous emission of particles and/or radiation. Ans:  False 91. An allotrope is a mixture of forms of the same compound that exist in the same physical state under the same conditions of temperature and pressure. Ans:  False 92. An ionizable hydrogen atom is a hydrogen atom that separates from the molecule when the molecule is dissolved in a solution and becomes a hydrogen ion, H+. Ans:  True 93. What is the law that describes different samples of a given compound that always contain the same elements in the same mass ratio? Ans: law of definite proportions 94. What is the law of conservation of mass? Ans: Matter can be neither created nor destroyed. 95. How many neutrons are in 13C? Ans: 7 96. What name is given to the simplest organic compounds which only contain carbons and hydrogens? Ans: hydrocarbons 97. What is the name of Cu2O? Ans: Copper (I) oxide 98. What is the formula for sodium dichromate? Ans: Na2Cr2O7 99. What is the name given for the elements in Group 1A in the periodic table? Ans: Alkali metals 100. What is the name given for the elements in Group 7A in the periodic table? Ans: Halogens 101. Which group is given the name chalcogens? Ans: Group 6A 102. What are the three types of radiation produced by the decay of substances like uranium? Ans: Alpha, beta, and gamma radiation 103. Define ion. Ans: An ion is an atom or group of atoms that has a net positive or negative charge. 104. Fill in the blank spaces and write out all the symbols in the left hand column in full, in the form (i.e., include the appropriate values of Z and A as well as the correct symbol X). Symbol # protons # neutrons # electrons … 17 18 … Au … 118 … … … 20 20 Ans: Cl 17 18 17 Au 79 118 79 Ca 20 20 20 105. ________________ is the emission and transmission of energy through space in the form of waves. Ans: Radiation 106. _____________ is the negatively charged plate connected to a high-voltage source. Ans: Cathode 107. ______________ coined the term radioactivity to describe the spontaneous emission of particles and/or radiation. Ans: Marie Curie 108. ______________ are electrons that are deflected away from negatively charged plates. Ans: ? particles 109. ______________ are atoms that have the same atomic number (Z) but different mass numbers (A). Ans: Isotopes 110. _____________ have properties that are intermediate between those of metals and nonmetals. Ans: Metalloids 111. ____________ are the name given for the elements in Group VIIIA. Ans: Noble gases 112. _____________ compounds consist of two different elements. Ans: Binary 113. _________________ is defined as a mass exactly equal to one-twelfth the mass of one carbon-12 atom. Ans: One atomic mass unit 114. ________________ are one of two or more distinct forms of an element. Ans: Allotropes 115. When one of the hydrogen atoms in a molecule is replaced by a group of atoms, this group of atoms is known as a ________________. Ans: functional group 116. Briefly explain the relationship between hypothesis and experiment in the scientific method. Ans: A hypothesis should be capable of leading to a prediction which is testable by experiment. If the experimental result differs from the prediction, the hypothesis should be modified. 117. The table below describes four atoms. Atom A Atom B Atom C Atom D Number of protons 79 80 80 79 Number of neutrons 118 120 118 120 Number of electrons 79 80 80 79 Which atoms represent the same element? Ans: Atoms A and D represent the same element, Atoms B and C represent the same element. 118. In the early 1900s, Ernest Rutherford performed an experiment with gold foil, targets and alpha particles to probe the structure of the atoms. He observed that most of these alpha particles penetrated the foil undeflected. Realizing that atoms are electrically neutral (that is, they have equal numbers of protons and electrons) and that the mass of a proton is significantly greater than the mass of an electron, use Rutherford's data to propose a structural model of an atom. Ans: (Answers will vary.) Atoms are mostly empty space. The mass is concentrated mostly at the center of the atom. 119. Describe the contributions of Marie Curie. Ans: (note that answers will vary) Marie Curie discovered two new elements, and is one of three people to win two Nobel Prizes. She also suggested the term “radioactivity” to describe the spontaneous emission of particles and/or radiation. 120. State the two important experimental results (and the names of the responsible scientists) which enabled the mass of the electron to be determined. Ans: Thomson measured m/e, the mass-to-charge ratio. Millikan measured e, the charge. Thus, the mass m could be calculated. 121. Name the three important "laws" that were accounted for by Dalton's atomic theory. Ans: Laws of conservation of mass; definite composition; multiple proportions 122. Dalton's atomic theory has required some modifications in the light of subsequent discoveries. For any three appropriate postulates of Dalton's atomic theory: state the postulate in its original form and in one sentence, describe why the postulate has needed modification. Ans: Matter consists of atoms which are indivisible, cannot be created or destroyed. But, atoms are divisible, as the existence of subatomic particles shows. Atoms of one element cannot be converted into atoms of another element. They can be converted in various nuclear reactions, including radioactive decay. Atoms of an element are identical in mass and other properties. Isotopes of an element differ in their masses and other properties. 123. Describe the difference between an empirical formula and a molecular formula. Ans: An empirical formula is the simplest chemical formula that has the smallest possible whole number ratio of atoms in the formula and a molecular formula is the true formula of a molecule which is a whole number multiple of its empirical formula. 124. Determine the average atomic mass of boron is the natural abundance of 10B weighing exactly 10.0129 amu is 19.9% and the natural abundance of 11B weighing exactly 11.0093 amu is 80.1%? Show all your work. Ans: (10.0129)(0.199) + (11.0093)(0.801) = 10.81 amu 125. Explain what is meant by an ionizable hydrogen atom. Ans: It is one that separates from the molecule upon dissolving and becomes a hydrogen ion, H+. 126. Describe what is meant by the term 'functional group' in organic chemistry. Ans: A functional group is a group atoms that have replaced one of the hydrogen atoms in an organic compound.