PA Problem Set 3 ANSWERS The Structure of the Atom Due Wed Oct 10 th Test Friday Oct 12 th Early Theories of Matter : USE YOUR TEXTBOOK!!! Conceptual questions 1) What are the major components of Democritus s Atomic Philosophy? (see pg 88) a. Matter is composed of empty space through which atoms move b. Atoms are solid homogeneous indestructible and invisible c. Different kinds of atoms have different sizes and shapes d. The differing properties of matter are due to the size, shape and movement of atoms e. Apparent changes in matter result from changes in the groupings of atoms and not from changes in the atoms themselves. 2) What is wrong with Democritus s ideas? There are several different types of atoms, they are made of protons, neutrons and electrons (which are all made of smaller particles called quarks, by the way). Atoms are heterogeneous, destructible and visible, and atoms can change in a nuclear decay reaction. 3) What are the 5 major components of Dalton s Atomic Theory? a. All matter is composed of small particles called atoms b. Atoms of the same element are the same. Atoms of a specific element are different from those atoms of any other element. c. Atoms cannot be created or destroyed or divided into smaller particles d. Different atoms combine in simple whole number ratios to form compounds e. In a chemical reaction, atoms are separated, combined or rearranged. 4) What is wrong with Dalton s Atomic Theory? Isotopes exist so atoms of the same element are not all the same. Atoms can be created and destroyed and broken into smaller particles. Nuclear reactions are a 4 th type of reaction. 5) What is correct in Dalton s Atomic Theory? The Law of Definite Proportions, atoms do exist, Chemical bonds are formed, broken or rearranged during a chemical reaction, and atoms of different elements are different. Practice Questions 6) True False Questions determine if the following statements are true or false according to Democritus s ideas about atoms. a. Atoms are divisible. FALSE b. Atoms are hard dense spheres FALSE c. Changes in matter are due to the changes in atoms. TRUE
7) True False Questions determine if the following statements are true or false according Dalton s Atomic Theory a. All matter is made of small particles called atoms. TRUE b. Atoms are divisible. FALSE c. Atoms of the same element are identical TRUE d. Atoms can be separated, combined or rearranged TRUE Extension Questions 8) What is a Scanning Tunneling Microscope? Briefly describe what it does and why it is an important tool for scientists. The STM is a high powered microscope that beams electrons off of a surface to indicate the distance from a probe to the surface. Three Dimensional models of the surface can be built from these very accurate (but very small) outputs. 9) Why do you think Dalton s Atomic theory is still taught in school, even though it is over 200 years old? Answers will vary.. but basically it is taught because it is a law of science Sub-Atomic Particles and the Nuclear Atom: USE YOUR TEXTBOOK!!! Conceptual Questions 10) The cathode ray tube was used to discover the electron. Re-Draw the diagram from your notes and include what the ray looks like when the + end of a magnet is brought near the ray. MAGNET M The ray will travel toward the + pole of the magnet because the particle of the ray are negatively charges. -- + cathode anode high voltage 11) What conclusion did Thomson draw from his observations? The atom is divisible! There are negatively charged particles in the atom that can be drawn out with electricity 12) Rutherford used radioactive material to fire positively charged particles at thin sheets of metal. a. What is the name of those particles? Alpha particles b. What is the composition of those particles? 2 protons, 2 neutrons 13) Create a diagram of Rutherford s Gold Foil Experiment. Be sure to include the following details: the alpha particles, the radioactive polonium, the zinc sulfide
lining, the gold foil, and these three locations of hits: the most hits, some hits, and only a few hits. ZnS lined ring 209 Po Po alpha particles (α) Au Most hits Very few hits some hits 14) What were Rutherford s two observations from his famous experiment? a. Most of the sparks were located directly behind the gold foil b. There were some (very few) sparks in front of the foil 15) What were the two conclusions that correspond to the Rutherford s two observations? Be sure to connect each conclusion with the appropriate observation. a. The atom is mostly empty space b. There is a small dense positive nucleus to the atom Practice Questions see back of pset for answers 16) Who determined that electrons exist? JJ Thomson 17) Who determined the mass of an electron? Robert Millikan 18) What is the mass of an e -? 9.1 x 10-28 g p + : 1.67 x 10-24 g n o = 1.675 x 10-24 g 19) Who determined that the nucleus of an atom exists? Rutherford 20) Who determined the charge of nucleus? Rutherford 21) What is the charge of the nucleus? Positive 22) Who determined that neutrons exist? Chadwick Extension Questions 23) Draw three historical pictures of an atom if we could take a picture of it be as detailed as possible a a. Dalton s Perspective b. Thomson and Millikan s Perspective b empty c. Rutherford and Chadwick s Perspective c empty 24) Propose a reason for a neutron to be ever so slightly more massive than a proton. Answers will vary, but the neutron is made of a proton and an electron think about how a beta particle is formed. 25) Diagram one of the experiments on the atom on one page of blank paper. Make it colorful, big, label it these will be posted in the room as we progress through our study of the atom.- check out the ones that were submitted in the class
How Atoms Differ: USE YOUR TEXTBOOK!!! Conceptual Questions 26) Define the following terms a. Atomic number the number of protons in an atom -identifies the element b. Isotope an atom of an element with a different number of neutrons than another atom of the same element c. Average Atomic Mass the weighted average of the isotopes of an element represented in the periodic table of elements d. Percent Abundance the amount of each isotope that is found in nature 27) How are isotopes of the same element alike? They must have the same number of protons and electrons to be the same element and to be an atom. 28) How are isotopes of the same element different? They must have different number of neutrons. 29) What sub-atomic particle(s) identify/(ies) an element? protons 30) What sub-atomic particle(s) determine(s) the isotope of an element? neutrons 31) Use the data below to calculate the average atomic weight for compound X. Then use your periodic table to identify element X. Isotope 1 = 90. 00 %, 39 a.m.u. Isotope 2 = 9.000 %, 40 a.m.u. Isotope 3 = 1.000 %, 41 a.m.u. 39 amu x.9 + 40 amu x 0.09 + 41 amu x 0.01 = 39.11 amu Potassium 32) One of the stable isotopes of tins is tin-119. The atomic number of tin is 50. How many protons, neutrons and electrons are in one atom of this isotope of tin? Tin has 50 protons and because it is a neutral atom, 50 electrons. The mass number is 119, so there must be 69 neutrons. 33) What is the atomic mass of an isotope of potassium that has 21 neutrons? Potassium has 19 p +, so an isotope with 21 n o will have a mass of 40 amu Practice Questions 34) Fill in this table for each atom or ion. You may write on the Problem Set rather than re-draw the table in your responses. see back page of pset Isotope Symbol # p + #e - #n o Atomic Mass Charge Name Number Number Tin - 118 118 68 0 50 Sn 19 18 40
Extension Questions 35) List the steps needed to calculate the average atomic mass if you are given the relative abundance and mass of each isotope known to exist. Sum the products of the mass times the relative abundance of each isotope. 36) Nitrogen has two naturally occurring isotopes: nitrogen-14 and nitrogen-15. The average atomic mass of nitrogen is 14.0007 amu. Which isotope is more abundant? Explain. Nitrogen 14 is more abundant because the average atomic mass is much closer to the mass of nitrogen 14 than it is to nitrogen- 15. Radioactive Decay: USE YOUR TEXTBOOK!!! Conceptual Questions 37) State the law of conservation of mass. Mass can never be created or destroyed in a chemical reaction unless it is transformed in to energy through E = mc 2 38) Why are atoms unstable? Typically the nucleus of an unstable element has too many neutrons. 39) How do unstable atoms gain stability? By emitting nuclear radiation (in the form of neutrons, alpha particles, beta particles) or undergoing fission. 40) A radioactive element having atomic number 82 and atomic mass 214 loses a beta particle, 0 1 β. What is the resulting particle? Bismuth-214 41) What type of decay is the reaction below, and what isotope completes this nuclear 27 equation? 13 Al + 2 1 H 4 2 He +? alpha decay 25 12 Mg 42) Complete this chart on the three types of radioactive decay Type Symbol Mass (amu) Charge Alpha 4 α 4 mas units +2 He 2 Beta 0 β 1/2000 th of a mass -1-1 e - unit Gamma γ 0 mass units No charge 43) If the radioactive atom 238 92 U emits an alpha particle, the atom remaining is represented by (A) 238 92U (B) 236 92Th (C) 234 92U (D) 234 90Th (E) 234 91 Pa 44) What term completes this equation? (A) 4 2 He (B)2 1H (C) 1 1H (D) 0 1e 30 14Si +? 32 16 S + 1e 0
45) What particle is emitted when lead 214,( 214 82 Pb ), undergoes natural radioactive decay to bismuth 214, 214 83Bi? (A) an alpha particle, 4 2He (C) a proton, 1H 1 (B) a beta particle, 1e 0 (D) a neutron, 1 0n Extension Question 46) Recently Alexander v Litvinenko was poisoned by radioactive polonium-210. a. Research who he was and why he was poisoned. Google it b. Find out what polonium-210 does to people. Google it c. Write the nuclear reaction of polonium-210 decaying into lead-206 via an alpha decay. 210 206 4 84 82 2 Nuclear Chemistry USE YOUR TEXTBOOK!!! Conceptual questions. 47) Define the following terms: a. critical mass the minimum amount of radioactive material that is required to support spontaneous nuclear chain reaction. b.decay the process where unstable nuclei deteriorate into more stable nuclei c. Fission the splitting of the nucleus of an atom into nuclei of lighter atoms, releasing energy. d.fusion a nuclear reaction where two or more nuclei merge together to form one more massive nuclei e. half life the mount of time it takes for half the mass of a sample of radioactive material to decay. f. Transmutation changing one element into another by altering its nucleus 48) Make (or find) a graphical timeline of the development of modern atomic theory with at least 10 important dates and/or discoveries. Do research 49) Which type of radiation generates the highest energy is the hardest to block? a. Alpha b. beta c. gamma d. neutron Practice Questions 50) Finish the following nuclear reactions. Tell if they are alpha or beta decays. a. 238 234 4 c. 222 218 4 92 90 2 86 84 2 b. 19 0 Po 19 Pb + He + γ U Th + He Rn Po + He d. 210 210 0 F _β + Ne At Rn + β 9-1 10 85 86 - -1 51) How many grams of sample are left after 20 minutes if 100 grams start decaying with a half life of 5 minutes? 20 min = 4 ½ lifes 1 ½ life = 50 g, 2 ½ life = 25 g, 3½ life = 12.5 g, 4½ life = 6.25 g,
52) How long will it take 100 grams of radioactive sample to decay so that only 12.5 grams remain and the samples half life is 3 days? 3 day = 50 g, 6 days = 25 g, 9 days = 12.5 g 53) How long is the half life of an isotope if only 2.0 grams of sample remain from a 64 gram sample after 30 years? 64 32 16 8 4 2, so five half lifes have passed in 30 years each half life must be 30 / 5 = 6 years long 54) Element number 96 is named Curium. Do you think Marie and Pierre Curie did enough in the advancement of science to have an element named after them? Explain. Answers will vary, but once researching these two people it ought to be clear that their work in the field is certainly worthy of life long commemoration by having an element named after them. 55) Thorium-231 is a radioactive isotope of thorium. It decays in ten steps to form lead-207. The ten steps are: β, α, α, β, α, α, α, β, β, α. Write this decay series. 231 90 Th 0-1β + 231 91Pa 231 91 Pa 4 2He + 227 89Ac 227 89 Ac 4 2He + 223 87Fr 223 87 Fr 0-1β + 223 88Ra 223 88 Ra 4 2He + 219 86Rn 219 86 Rn 4 2He + 214 84Po 214 84 Po 4 2He + 210 82Pb 210 82 Pb 0-1β + 210 83Bi 210 83 Bi 0-1β + 210 84Po 210 84 Po 4 2He + 206 82Pb 34) Isotope Name tin - 118 Potassium-40 Fluorine -19 Nitrogen -14 tellurium - 128 Symbol # p + #e - #n o Atomic Mass Charge Number Number 50 50 68 50 118 0 118 50 40 +1 19 19 F -1 9 14-3 7 128 52 Sn K N Te 19 18 21 19 40 +1 9 10 10 9 19-1 7 10 7 7 14-3 52 52 76 52 128 0