The Structure of the Atom - Supplemental Problems

The Structure of the Atom - Supplemental Problems 1. Use the periodic table to complete the following table. Element Atomic Number Protons Electrons Li 3 3 3 Fr 87 87 87 Np 93 93 93 Hg 80 80 80 Tl 81 81 81 Re 75 75 75 B 5 5 5 2. Give the number of protons, electrons, and neutrons in each of the following atoms. 108 a) 47 𝐴𝑔 Answer: p= 47, e= 47, n= 61 b) 40 20 𝐶𝑎 Answer: p= 20, e= 20, n= 20 c) 23 11 𝑁𝑎 Answer: p= 11, e= 11, n= 12 3. Name each isotope, and write it in symbolic notation. a) atomic number 26; mass number 56 Answer: 56 26 𝐹𝑒; iron-56. b) atomic number 29; mass number 64 Answer: 64 29 𝐶𝑢; copper-64. c) atomic number 17; mass number 37 Answer: 37 17 𝐶𝑙; chlorine-37. 4. How many protons, electrons, and neutrons are in each of the following isotopes? a) uranium-235 Answer: 92 protons, 92 electrons, 143 neutrons (235 – 92 = 143) b) hydrogen-3 Answer: 1 proton, 1 electron, 2 neutrons (3 – 1 = 2) c) silicon-29 Answer: 14 protons, 14 electrons, 15 neutrons (29 − 14 = 15) 5. How many neutrons does europium-151 have? What is the isotope’s mass number? Answer: Number of neutrons = mass number - atomic number = 151 − 63 = 88 neutrons. The mass number is 151. 6. How many more neutrons does thorium-230 have than protons? How many electrons does thorium-230 have? Answer: Number of neutrons = mass number – atomic number = 230 − 90 = 140 neutrons Difference between the number of protons and the number of neutrons 140 − 90 = 50 Therefore, Thorium-230 has 50 more neutrons than it does protons. Atomic number = number of protons - number of electrons Therefore, thorium-230 has 90 electrons. 7. Show that the mass number and the number of protons are conserved in the following nuclear equation: 234 92 𝑈 → 230 90𝑇 ℎ + 42𝐻 𝑒 Answer: Mass number: 234 → 230 + 4 Atomic number: 92 → 90 + 2 8. a) b) c) d) Give the mass number of each isotope. Be with 5 neutrons Ga with 39 neutrons Si with 16 neutrons Ti with 26 neutrons Answer: a) 5 neutrons + 4 protons = 9; b) 39 neutrons + 31 protons = 70; c) 16 neutrons + 14 protons = 30; d) 26 neutrons +22 protons = 48 9. a) b) c) Give the atomic number of each isotope. magnesium-25 bromine-79 antimony-121 Answer: a) 12; b) 35; c) 51. 10. Neon has two isotopes: neon-20 and neon-22. a) Which isotope has the greater mass? b) Which has more neutrons? c) Which has more protons? d) Which has more electrons? Answer: a) Neon-22; b) Neon-22; c) They have an equal number of protons.; d) They have an equal number of protons. 11. Use the table below to calculate the atomic mass of element X. Then use the periodic table to identify the element. Show all your work. Isotope Mass (amu) 16 15.995 𝑋 17 16.999 𝑋 18 17.999 𝑋 Answer: Mass contribution = (mass)(percent abundance) Percent Abundance 99.762 0.038 0.20 16 𝑋: (15.995 𝑎𝑚𝑢)(99.762) = 15.957 𝑎𝑚𝑢 17 𝑋: (16.999 𝑎𝑚𝑢)(0.038) = 0.0065 𝑎𝑚𝑢 18 𝑋: (17.999 𝑎𝑚𝑢)(0.20) = 0.036 𝑎𝑚𝑢 Atomic mass of 𝑋 = 15.957 𝑎𝑚𝑢 + 0.0065 𝑎𝑚𝑢 + 0.036 𝑎𝑚𝑢 = 16.000 𝑎𝑚𝑢 The element is oxygen. 12. Magnesium has three isotopes. Magnesium-24 has a percent abundance of 78.99%. Magnesium-26 has a percent abundance of 11.01%. What is the percent abundance of magnesium-25? Assume that there are no other magnesium isotopes. Answer: All the percentages should add up to 100%. Therefore: 100% (percent abundance of magnesium-24) + (percent abundance of magnesium25) + (percent abundance of magnesium-26) 100% = 78.99% + (percent abundance of magnesium-25) + 11.01% Percent abundance of magnesium-25 = 100% - (78.99% + 11.01%) = 10.00% 13. Calculate the atomic mass of iridium. Iridium has two isotopes. Iridium-191 has a mass of 191.0 amu and a percent abundance of 37.58%. Iridium-191 has a mass of 193.0 amu and a percent abundance of 62.42%. Show all your work. Answer: Mass contribution = (mass)(percent abundance) Ir-191: (191.0 amu)(37.58%) = 71.78 amu Ir-193: (193.0 amu)(62.42%) = 120.5 amu Atomic mass of Ir = 71.78 amu + 120.5 amu = 192.3 amu 14. An element has three naturally occurring isotopes. Isotope 1 has a mass of 19.992 amu. Isotope 2 has a mass of 20.994 amu. Isotope 3 has a mass of 21.991 amu. Relative abundance Isotope 1 = 90.51% Isotope 2 = 0.27% Isotope 3 = 9.22% a) Draw a pie graph that shows the relative abundance of each isotope. b) Calculate the atomic mass of the element. c) Identify the element, using the periodic table. Answer: a) b) Mass contribution = (mass)(percent abundance) Isotope 1: (19.992 amu)(90.51%) = 18.10 amu Isotope 2: (20.994 amu)(0.27%) = 0.057 amu Isotope 3: (21.991 amu)(9.22%) = 2.03 amu Atomic mass = 18.10 amu + 0.057 amu + 2.03 amu = 20.19 amu c) The element is neon. 15. An element has three naturally occurring isotopes. Information about each isotope is summarized below. Isotope Mass (amu) Percent Abundance 1 23.985 78.10 2 24.946 10.13 3 25.983 11.17 a) Find the atomic mass of this element. Show all your work. b) Identify the element, using the periodic table. c) Write each isotope in symbolic notation. Answer: a) Mass contribution = (mass)(percent abundance) Isotope 1: (23.985 amu)(78.70%) = 18.88 amu Isotope 2: (24.946 amu)(10.13%) = 2.531 amu Isotope 3: (25.983 amu)(11.17%) = 2.902 amu Atomic mass of element = 18.88 amu + 2.527 amu + 2.902 amu = 24.31 amu b) The element is magnesium. c) 25 26 24 12 𝑀𝑔; 12𝑀 𝑔; 12𝑀 𝑔 16. The isotope carbon-14 can be used to deter-mine the ages of objects that were once living, such as wood, bones, and fossils. While alive, living things take in all the isotopes of carbon, including carbon-14. Carbon-14 undergoes radioactive decay continuously. After an organ-ism dies, the carbon-14 in its body continues to decay. However, its body no longer takes in new carbon-14. Thus, by measuring how much carbon-14 a onceliving object contains and comparing it with the amount of carbon-14 in a currently living thing, you can determine the age of the object. a) In terms of subatomic structure, how does carbon-14 differ from carbon-12 and carbon13? b) How is carbon-14 like carbon-12 and carbon-13? c) Carbon-14 emits a beta particle as it decays. What atom does carbon-14 decay to? d) Write an equation to represent the decay of carbon-14. Answer: a) Carbon-14 has 8 neutrons, carbon-12 has 6 neutrons, and carbon-13 has 7 neutrons. Carbon-14 has a larger atomic mass than the other two isotopes have. b) All three isotopes have 6 protons and 6 electrons. They all show the same physical and chemical properties of the element carbon. c) If carbon-14 emits a beta particle, then it must become nitrogen-14 (-1 + x = 6; thus, x = 7, which is the atomic number of nitrogen). d) The equation that shows this change is: 14 6𝐶 →147 𝑁+−10 𝑒