Accelerated Chemistry Study Guide Atomic Structure, Chapter 3 Terms and definitions atom ion law of constant composition isotope atomic theory of matter mass number cathode ray tube atomic mass electron nuclear reaction radioactivity strong nuclear force nucleus radioactive decay proton nuclear equation neutron alpha radiation atomic mass unit beta radiation atomic number gamma radiation Page 1 of 46
Specific topics to know Development of Atomic Theory Composition of the atom balancing nuclear equations: both atomic number and mass number must be conserved Important People in the Development of Atomic Theory Democritus Antoine Lavoisier Joseph Louis Proust John Dalton Michael Faraday Benjamin Franklin J.J. Thomson Robert Millikan Henri Becquerel Marie and Pierre Curie Ernest Rutherford Henry Moseley Page 2 of 46
The World of Chemistry Episode 6 - The Atom 1. What are the three basic components (particles) that make up an atom? 2. What are the two regions of any atom? 3. How does the size of the nucleus compare to the size of an atom? 4. What is the Scanning and Tunneling electron Microscope (STM) used for? 5. What holds the electrons and the nucleus together? 6. Unlike charges ; like charges.. 7. What are the charges on the electron, the proton, and the neutron? 8. Why is the overall charge of the atom neutral? 9. What did Rutherford's gold foil experiment show? 10. When two atoms meet, what parts of the atoms interact? 11. What are some ways that signals from the atom can be used? Page 3 of 46
Chapter 3 Notes: Accelerated Chemistry Early models of the atom: Democritus the first to propose the existence of atoms Antoine Lavoisier discovered the law of conservation of matter Proust-discovered the law of constant composition: that a given compound always contains elements in the same proportion by mass. Ex: all samples of CO 2 are ALWAYS 12 g carbon for every 32 g oxygen John Dalton proposed the first atomic theory of matter using Proust s and Lavoiser s laws: --matter is composed of indivisible particles called atoms --atoms of a given element are identical, atoms of different element are different --atoms cannot be created or destroyed in a chemical reaction --a given compound always has the same relative ratio of atoms of different elements Michael Faraday suggested that the structure of atoms was related to electricity but. JJ Thomson discovered the electron in his cathode ray tube experiments. Thomson found that electrons have a negative charge because they were attracted to a positive charge and that they had mass because they made a paddle wheel spin. He calculated the ratio of charge to mass, but not the charge or mass of a single electron. Robert Millikan discovered the mass of a single electron by using Thomson s charge to mass ratio and an experiment with charged oil droplets. He deduced the charge on a single electron in his experiment, which showed that oil droplets in the experiment always had charges that were a multiple of 1.60 X 10-19 Coulombs. Henri Becquerel discovered radioactivity, the spontaneous emission of radiation from an element. Ernest Rutherford s gold foil experiment proved two things: 1. the existence of the nucleus and 2. that the nucleus was positively charged and very small relative to the rest of the atom. He disproved the plum pudding model of JJ Thomson, his own mentor! Page 4 of 46
Atomic structure, isotopes and isotope notation. Subatomic Particle Location Charge Relative mass Proton In nucleus +1 1 amu Neutron In nucleus neutral/0 1 amu Electron Outside of nucleus -1 1/1836 amu Atomic number the number of protons in an atom. This number is UNIQUE to every atom. In other words, sodium atoms (and ONLY sodium atoms) have 11 protons. Notice that the periodic table is arranged in order of increasing atomic number. In a neutral atom the number of protons is equal to the number of electrons. The positively charged protons cancel out the charge of the negatively charged electrons, making the atom neutral. Ions are formed when an atom gains or loses electrons. Since electrons are negatively charged, gaining electrons makes an ion more negative, while losing electrons makes an ion more positive. Ex: Na + is formed when Na, loses one electron. Na + has 11 protons (atomic # = 11) and 10 electrons Mg 2+ is formed when Mg loses two electrons. Mg 2+ has 12 protons and 10 electrons S 2- is formed when S gains two electrons. S 2- has 16 protons and 18 electrons Cl - is formed when Cl gains one electrons Cl - has 17 protons and 18 electrons Mass number the number of protons plus the number of neutrons in an atom. This number is different for different isotopes (see below) Isotopes have the same number of protons but different numbers of neutrons. Here are the three naturally occurring isotopes of carbon: 12 13 14 A C C C X 6 6 6 Z carbon-12 carbon-13 carbon-14 Notice that the atomic number (abbreviated Z) is the same for each isotope because these are all types of carbon. Notice that the mass number (abbreviated A) is different for each isotope above. Make sure that you can predict the number of neutrons in each isotope above. C-12 has 6 neutrons, C-13 has 7 neutrons, and C-14 has 8 neutrons. Page 5 of 46
The mass of an atom The amu (atomic mass unit) is approximately the mass of either a proton or a neutron. More precisely, the amu is defined so that a carbon-12 atom has a mass of exactly 12 amu. 1 amu = 1.66 X 10-24 g This equality appears a bit bizarre at first until you consider that the size of an amu works out perfectly with something you ll learn more about later called the mole A mole of carbon-12 atoms (a mole of C-12 means a sample containing 6.022 X 10 23 of these atoms) has a mass of exactly 12 grams. So this happens: 1 carbon-12 atom = 12.0000000. amu 1 mole of carbon-12 atoms = 12.0000000.. grams The masses of the elements on the periodic table are called the atomic weights or the atomic masses of the elements. They are NOT the same thing as the mass number of an isotope (defined above). The atomic mass of an element is determined by taking a weighted average of all the masses of all the naturally occurring isotopes along with their percent abundances: Isotope Mass Number Mass Natural Abundance Carbon 12 C 12 12.000 (exactly 12) 98.99% 13 C 13 13.003 1.11% Atomic mass = (Isotope Mass)(Natural Abundance as a decimal) + (Isotope Mass)(Natural Abundance). = 12.0000(0.9899) + (13.003)(0.0111) = 12.01 Try the data for silicon on page 110. Page 6 of 46
Nuclear Equations Alpha decay decay of a radioactive nucleus in which an alpha particle is produced example 2 4 He or 2 4 210 Po 4 84 2 He + 206 82 Pb Beta decay decay of a radioactive nucleus in which an beta particle (an electron) is produced and a neutron is converted into a proton example 0 0 1e or 1 210 83 Bi 210 Po + 0 1e 84 Specific topics to know nuclear stability types of radioactive decay balancing nuclear equations: both atomic number and mass number must be conserved Page 7 of 46
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Cathode Ray Tube (CRT) Thomson s Plum Pudding Model Page 9 of 46 1
Discovering Atomic Structure Robert Millikan Millikan s Oil Drop Experiment Bags of oranges Page 10 of 46 2
Discovering Atomic Structure Ernest Rutherford: gold foil experiment Rutherford s Gold Foil Experiment Expected Actual Page 11 of 46 3
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Model 1 Dalton s Experiment 0.6 L of hydrogen gas + 0.6 L chlorine gas yields 1.2 L muriatic acid gas 1.2 L of hydrogen gas + 0.6 L chlorine gas yields 1.2 L muriatic acid gas + 0.6 L hydrogen gas 0.6 L of hydrogen gas + 1.2 L chlorine gas yields 1.2 L muriatic acid gas + 0.6 L chlorine gas 1.2 L of hydrogen gas + 1.2 L chlorine gas yields 2.4 L muriatic acid gas Page 15 of 46
Dalton s 5 Part Atomic Theory (1803) All elements are made of atoms. Atoms of an element are identical. Atoms of different elements are different. Atoms combine in simple whole number ratios to make compounds. Atoms may rearrange in chemical reactions, but are not changed in the reaction. Dalton s Model of the Atom: Dalton described the atom (his model) as a small hard sphere. All elements were made of many of these spheres. Since atoms of each element are different from each other, the sphere for each element would be slightly different. Critical Thinking Questions 1. Evaluate the information provided for Dalton s experiment. Which one of the five parts of his theory is best supported by the experimental data? Use specific data from the model to explain how the data supports his theory. 2. What part of Dalton s model of the Atom do we still agree with today? What part of the model has been discarded? Page 16 of 46
Model 2 Thomson s Experiments (1897) Part 1: Thomson used a hollow glass tube with a metal plate on either end. Thomson removed the air from the tube, and connected the tube to an electricity source. He found that rays travelled across the tube from the cathode to the anode. Part 2: Thomson exposed the ray to a magnet and found that the ray bent toward the positive end of a magnet, and away from the negative end of a magnet. Part 3: Thomson used an electric field to measure the mass to charge ratio of the ray. He found this ratio to be almost 2000 times larger than the mass to charge ratio for a charged hydrogen atom. So.. either the ray particless had a HUGE charge, or a very small mass. Critical Thinking Questions 3. What technological advancement was requiredd for Thomson to conduct his experiments? 4. What part of the atom did Thomson discover?? Give specific evidence from his experiments to support your claim. Page 17 of 46
Thomson s Model of the Aton: Thomson held on to Dalton s idea that atoms were solid objects. He modified Dalton s model to add a positively charged base material that had small negatively charged particles imbedded. He called this the Plum Pudding model. 5. What part of Thomson s model of the Atom do we still agree with today? What part of the model has been discarded? Model 4 Rutherford s Experiment (1911) Rutherford set out to test Thomson s model of the atom using alpha particles. Alpha particles are essentially a Helium nucleus that is emitted from a larger atom during radioactive decay. These small particles are able to pass through paper, and thin layers of other materials. The experiment involved using a sheet of gold that was only 2-3 atoms thick. The alpha particles were released from a lead box through a slit. 99.999% of the particles passed directly through the gold foil as if it wasn t there. A very small number of particles were deflected, some a little, some were deflected almost straight back. Page 18 of 46
Critical Thinking Questions 6. What technological advancement was required for Rutherford to conduct his experiment? 7. What part of the atom did Rutherford discover? Give specific evidence from his experiment to support your claim. Rutherford s Model of the Atom: Rutherford held on to Thomson s idea that atoms were made up of positive and negative parts. He modified Thomson s model to specify that the positive part of the atom was contained in a small, dense nucleus, and the electrons orbited the nucleus like planets orbit the sun. 8. What part of Rutherford s model do we still agree with today? What part of the model has been discarded? Page 19 of 46
Model 5 Bohr s Experiment (1922) Bohr observed that when a sample of hydrogen gas was exposed to electric current it released energy as light. When this light was viewed with a spectroscope, specific wavelengths of light were seen. Different wavelengths of light correspond to different levels of energy. Bohr used this same method to test other elements and found that each emitted its own distinct color of light, each made up of its own wavelength combinations. high energy low energy Bohr realized that this phenomenon was not possible with Rutherford s model of the atom, since electrons travelling in an elliptical orbit would produce a continuous rainbow of colors instead of the distinct lines seen. Page 20 of 46
Bohr s Model of the Atom: Bohr held on to Rutherford s idea that atoms were made up of a positive nucleus with electrons orbiting around the nucleus. He modified Rutherford s model to specify that the electrons travel in an orbit that is a set distance from the nucleus. This results in each electron orbit containing a specific amount of energy. Critical Thinking Questions 9. What property of atom behavior did Bohr discover? Give specific evidence from his experiment to support your claim. 10. What part of Bohr s model do we still agree with today? What part of the model has been discarded? 11. Our understanding of the atom has changed from Dalton to today. When changes were made to the model of the atom were all previous models thrown out, or were they modified? Why do you think this is the case? Page 21 of 46
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ChemQuest 8 Information: Structure of the Atom Note the following symbols: (they are not to scale) = proton (positive charge) = electron (negative charge) = neutron (no charge) The following three diagrams are hydrogen atoms: The following three diagrams are carbon atoms: 1 1H 2 1H 3 1H Notice the type of notation used for atoms: 12 13 14 6C 6C 6C (6 protons, 6 neutrons) (6 protons, 7 neutrons) (6 protons, 8 neutrons) 12 13 14 6 C 6 C 6 C A Z X X = chemical symbol of the element Z = atomic number A = mass number,, and are notations that represent isotopes of carbon. 1 1H 2 1H 3 1 H, and are notations that represent isotopes of hydrogen. The part of the atom where the protons and neutrons are is called the nucleus. Page 25 of 46
Critical Thinking Questions 1 1H H 2 3 1 1H 1. How many protons are found in each of the following:? in? in? 1 1H H 2 3 1 1H 2. How many neutrons are found in each of the following:? in? in? 1 1H H 2 3 1 1H 3. How many electrons are found in each of the following:? in? in? 4. What structural characteristics do all hydrogen atoms have in common? 5. What structural characteristics do all carbon atoms have in common? 6. What does the mass number tell you? Can you find the mass number of an element on the periodic table? 7. What does the atomic number tell you? Can you find the atomic number of an element on the periodic table? 8. Define the term isotope. 9. How does one isotope of carbon differ from another isotope of carbon? Page 26 of 46
Information: Atoms, Ions, Masses of Subatomic Particles The atomic mass unit (amu) is a special unit for measuring the mass of very small particles such as atoms. The relationship between amu and grams is the following: 1.00 amu = 1.66 x 10-24 g Note the following diagrams comparing atoms and ions. Atom Ion 9 protons 10 neutrons 9 protons 10 neutrons 19 9 F mass = 18.9980 amu 19-1 9 F mass = 18.9985 amu Atom Ion 12 protons 12 neutrons 12 protons 12 neutrons 24 12 Mg mass = 23.9978 amu 24 2 12 Mg mass = 23.9968 amu Critical Thinking Questions 10. What is structurally different between an atom and an ion? Note: This is the ONLY structural difference between an atom and an ion. 11. In atomic mass units (amu), what is the mass of an electron? Page 27 of 46
12. Is most of the mass of an atom located in the nucleus or outside the nucleus? How do you know? 13. If protons and neutrons have the same mass, what is the approximate mass of a proton and neutron in atomic mass units (amu)? 14 14. The mass of 6 C is about 14 amu. Does this agree with what you determined in questions 11 and 13? 15. The charge (in the upper right hand corner of the element symbol) is 1 for a fluorine ion. Why isn t it +1 or some other number? 16. What is the charge on every atom? Why is this the charge? 17. How do you determine the charge on an ion? 18. An oxygen ion has a 2 charge. (Use your periodic table if necessary) a) How many protons does the oxygen ion have? b) How many electrons does the oxygen ion have? Page 28 of 46
Skill Practice 8 1. An atom has a mass number of 43 and it also has 21 electrons. a) How many protons does this atom have? b) What is the identity of this atom? c) How many neutrons does this atom have? 2. What is an isotope? Give an example. 3. A certain ion has an atomic number of 16, a mass number of 33, and 18 electrons. a) What is the charge on the ion? b) What is the identity of this ion? c) How many neutrons does the nucleus of this ion have? 4. Tritium (an isotope of hydrogen) has 2 neutrons. How many protons does it have? What is its mass number? 5. What is the charge on a magnesium ion that has 10 electrons? 6. How many neutrons are there in a chromium atom with a mass number of 54? 7. Substance E has 29 protons, 28 electrons, and 34 neutrons. Substance F has 29 protons, 27 electrons, and 34 neutrons. Substances E and F can be categorized as A) different elements B) ions C) isotopes D) nuclides E) nucleons 8. The element with 38 protons and 45 neutrons could correctly be identified as which element? 9. Complete the following table: Symbol # of neutrons # of protons # of electrons Atomic # Mass # 136 2 56 Ba 25 25 56 120 79 79 21 20 18 Page 29 of 46
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ChemQuest 9 Information: Weighted Averages Examine the table of student test scores for five tests they have taken. Test Student A Student B 1 95 76 2 74 88 3 82 90 4 92 81 5 81 72 Average Grade Critical Thinking Questions 1. Calculate the average grade for students A and B and enter the average in the table above. 2. If you know a student s average grade can you tell what the student s individual test scores were? Explain. 3. Suppose student C had an average of 83%. On each of his five tests he scored either 65% or 95%. Which score occurred more often? Explain. 4. What if the teacher decided that test five would count for 40% of the final grade and test four would count for 30% of the final grade and each of the other tests would count for 10%. Calculate the new average for each student. Note: this is called the weighted average. Student A s new average: Student B s new average: Page 35 of 46
Information: Average Atomic Mass On the periodic table you can find the average atomic mass for an element. This average is a weighted average and it tells you the average mass of all the isotopes of an element. The periodic table does not contain mass numbers for individual atoms, instead you can find the average mass of atoms. The average atomic mass is calculated just how you calculated the weighted average in question 4 above. Critical Thinking Questions 5. Neon has three different isotopes. 90.51% of neon atoms have a mass of 19.992 amu. 0.27% of neon atoms have a mass of 20.994 amu. 9.22% of neon atoms have a mass of 21.991 amu. What is the average atomic mass of neon? 6. Chlorine-35 is one isotope of chlorine. (35 is the mass number.) Chlorine-37 is another isotope of chlorine. How many protons and how many neutrons are in each isotope of chlorine? 7. Of all chlorine atoms, 75.771% are chlorine-35. Chlorine-35 atoms have a mass of 34.96885 amu. All other chlorine atoms are chlorine-37 and these have a mass of 36.96590. Calculate the average atomic mass of chlorine. 8. Do your answers for questions 5 and 7 agree with the average atomic masses for neon and chlorine on the periodic table? Page 36 of 46
Skill Practice 9. Complete the following table. Symbol # of neutrons # of protons # of electrons Atomic # Mass # 31 15 P 28 13 Al 3 38 38 80 119 50Sn 84 84 210 8 7 10 10. A certain element has two isotopes. One isotope, which has an abundance of 72.15% has a mass of 84.9118 amu. The other has a mass of 86.9092 amu. Calculate the average atomic mass for this element. 11. Given the following data, calculate the average atomic mass of magnesium. Isotope Mass of Isotope Abundance Magnesium-24 23.985 78.70% Magnesium-25 24.986 10.13% Magnesium-26 25.983 11.17% Page 37 of 46
Skill Practice 9 1. A certain element exists as three different isotopes. 24.1% of all the isotopes have a mass of 75.23 amu, 48.7% have a mass of 74.61 amu, and 27.2% have a mass of 75.20 amu. a. What is the average atomic mass of this element? b. Use your periodic table to determine which element this is. 2. An element exists as 4 different isotopes. 4.35% have a mass of 49.9461 amu, 83.79% have a mass of 51.9405 amu, 9.50% have a mass of 52.9407 amu, and 2.36% have a mass of 53.9389 amu. a. What is the average atomic mass of this element? b. What is the identity of this element? 3. Calcium has three different isotopes. One has a mass of 35.00 amu; another has a mass of 41.00 amu; and another has a mass of 40.00 amu. Which isotope is the most abundant of the three? (HINT: Look at the periodic table at calcium s average atomic mass.) 4. Several isotopes of a certain atom X exist. 4.35% of all X atoms have a mass of 39.946 amu. 83.79% have a mass of 41.941 amu, 9.50% have a mass of 42.941 amu, and 2.36% have a mass of 43.939 amu. What is the average atomic mass of atom X? Page 38 of 46
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Name Period Date Accelerated Chemistry 2017-2018 Practice Quiz Chapter 3 (54 points) I. Definitions (2 points each) Define the following: 1. law of constant composition 2. atom 3. ion 4. alpha particle 5. nucleus II. Contributions to Atomic Theory. How did each of the following contribute to the development of Atomic Theory? (2 points each, except Thomson 4 points) 6. Michael Faraday 7. Joseph Louis Proust 8. J.J. Thomson (2 contributions) 9. Henri Becquerel 10. Ernest Rutherford Page 43 of 46 Page 1 of 4.
Name Period Date III. Free Response 11. List the four postulates of Dalton s Atomic Theory of Matter. (8 points) a. b. c. d. 12. There are 3 isotopes of the undiscovered element, Ue. The mass in amu and the relative abundance of two isotopes are given below. Use these data to calculate the average atomic mass of Ue. Show your work. (8 points) Isotope Mass (amu) Abundance (%) Ue-400 399.9876 0.02 Ue-401 400.9903? Ue-402 401.9957 30.96 Page 2 of 4. Page 44 of 46
Name Period Date Consider the notation given and the key below in answering #13-14. Proton Neutron Electron 13. Draw a picture of the particle described above. (4 points) 14. Draw a picture of an isotope of the particle represented above. (3 points) 15. How many protons, neutrons, and electrons does Po 2- have? (3 points) protons neutrons electrons 16. What is the difference between mass number and average atomic mass? (2 points) Page 45 of 46 Page 3 of 4.
Name Period Date Figure 3-2 17. Figure 3-2 illustrates the behavior of alpha, beta, and gamma radiation as a beam is passed between charged plates. Which letter represents the path of the gamma radiation? a c b d 18. In Figure 3-2, which ray would probably have the least penetrating power? a c b d Page 4 of 4. Page 46 of 46