Name: The Structure of the Atom Date: Unit 3 Atomic Structure, Isotopes and Average Atomic Mass Homework Chemistry 1 1. Indicate whether each of the following statements is true or false. If a statement is false, correct the statement so that it becomes true. a. In his cathode ray tube experiments, J. J. Thomson obtained beams of different types of particles whose nature depended on which gas was contained in the tube. b. Thomson assumed that there must be positively charged particles in the atom, since isolated atoms have no overall charge. c. In the plum pudding model of the atom, the atom was envisioned as a sphere of negative charge in which positively charged electrons were randomly distributed. 2. Indicate whether each of the following statements is true or false. If false, correct the statement so that it becomes true. a. Rutherford's bombardment experiments with metal foil suggested that alpha particles were being deflected by coming near a large, negatively charged atomic nucleus. b. The proton and the electron have similar masses but opposite electrical charges. c. Most atoms also contain neutrons, which are slightly heavier than protons but carry no charge. Introduction to the Modern Concept of Atomic Structure 3. What uncharged particles are found in the nuclei of most atoms? 4. Do the proton and the neutron have exactly the same mass? How do the masses of the proton and the neutron compare to the mass of the electron? 5. Which particles make the greatest contribution to the chemical properties of an atom? Isotopes 6. True or false? Atoms that have the same number of neutrons but different numbers of protons are called isotopes. 7. True or false? The mass number of a nucleus represents the number of protons in the nucleus. 1
8. How did Dalton's atomic theory have to be modified after the discovery that several isotopes of an element may exist? 9. Write the atomic symbol ( A Z X) for each of the isotopes described below. a. Z = 8, number of neutrons = 9 b. the isotope of chlorine in which A = 37 c. Z = 27, A = 60 d. number of protons = 26, number of neutrons = 31 e. the isotope of I with a mass number of 131 f. Z = 3, number of neutrons = 4 10. How many protons and neutrons are contained in the nucleus of each of the following atoms? Assuming each atom is uncharged, how many electrons are present? a. b. c. d. e. 244 94 Pu = p, n, e name 241 95 Am = p, n, e name 227 89 Ac = p, n, e name 133 55 Cs = p, n, e name 193 77 Ir = p, n, e name Hydrogen Isotopes Atoms are made up of subatomic particles, such as protons, neutrons and electrons. The nuclei of atoms that make up isotopes of an element differ. There are three known isotopes of hydrogen. Make a drawing that represents each of these isotopes. e 2p 2n e Helium-4 Protium Deuterium Tritium Hydrogen-1 Hydrogen-2 Hydrogen-3 2
11. Do the numbers of electrons for neutral isotopes of the same elements differ? 12. Do the number of protons for such isotopes differ? 13. Do the number of neutrons for such isotopes differ? 14. Do the atomic numbers for such isotopes differ? Explain. 15. Do the mass numbers for such isotopes differ? Explain. Average Atomic Mass Problems 16. What is the average atomic mass, in amu, of the element copper if it is composed of 69.5% of an isotope of atomic mass 63.00 and 30.5% of an isotope with an atomic mass of 65.00? Consider sig figs when expressing your answer. 17. Calculate the average atomic mass of lithium, which occurs as two isotopes that have the following atomic masses and abundances in nature: 7.30%, 6.017 amu and 92.7%, 7.018 amu. Consider sig figs when expressing your answer. 3
18. Calculate the average atomic mass of chromium, given the following percent abundances and atomic masses: 4.350% 49.946 amu; 83.790% 51.941 amu; 9.500% 52.941 amu; 2.360% 53.939amu. Consider sig figs when expressing your answer. 19. The four isotopes of lead are listed below, each with its percent abundance. Calculate the average atomic mass of lead. a. Isotope #1-82 protons, 122 neutrons - 1.37% b. Isotope #2-82 protons, 124 neutrons - 26.26% c. Isotope #3-82 protons, 125 neutrons - 20.82% d. Isotope #4-82 protons, 126 neutrons - 51.55% 4
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