On Wednesday, October 26th, 2011, you will be taking a test covering the material covered in Chapters 4 and 18 of the chemistry textbook for the class. The sections of one through seven will be tested in Chapter 4 and sections one through four will be tested in Chapter 18. You may want to read those sections specified, but know that all material that is covered by the exam is presented in the handouts and worksheets of the unit. The test will consist of both multiple choice questions and short answer / written questions. On the short answer portion, you may be asked to draw on diagrams to illustrate concepts within the unit of study. A practice test is available on the class calendar on the date Monday, October 24th, 2011. Realize the practice test only covers some of the concepts that are testable. Please use this blog post as the definitive listing of what you will be expected to show proficiency at on the exam. You will be given all equations that need to be utilized, a periodic table, and you will be able to use a calculator on the exam.
The history of the atom starting with John Dalton and the concept of the atom in the early 1800's to JJ. Thomson discovering the electron with a Crooke's tube to Ernest Rutherford discovering nucleus of the atom using the gold foil experiment are what many questions will center around. Know the significance of Dalton developing the atomic theory by using the laws of definite composition and multiple proportions as proof that atoms exist. Example: Water (H2O) and hydrogen peroxide (H2O2) both contain the elements hydrogen and oxygen. Both have different chemical and physical properties, so the concept of atoms allows for the building of these different chemical out of the same elements (Law of Multiple Proportions). The fact that water has two hydrogens and one oxygen gives it very specific chemical and physical properties. When water is poured on your head, a chemical property of water is that it will only wet your hair. It also has a very specific freezing poin, a very specific boiling point and a very specific density. All of these are physical properties of water that come from the two hydrogen to one oxygen ratio. To have these properties, the two to one ratio of hydrogen to oxygen must be, no other ratio will give the identical chemical and physical properties (Law of Definite Composition). Know about Thomson's Crooke's tube experiment for discovering the electron. Be able to diagram / discuss that the particle beam seen inside of the Crooke's tube could not be a charged atom of the lightest known element in the late 1800's (hydrogen), but rather, a particle with less mass based upon the amount of deflection the particle endured when subjected to a magnetic field. Know that Thomson's discovery of the electron and the subsequent discovery of the proton allowed the plum pudding model of the atom be developed. Be able to diagram / discuss the plum pudding model of the atom. Know about Rutherford's gold foil experiment for determining that the protons were located in the center of the atom in the nucleus and the electrons were outside of the nucleus. Be able to diagram / discuss how the plum pudding model predicted that the alpha particles would pass through the thin piece of gold foil. Be able to discuss / diagram the results that Rutherford actually saw from the gold foil experiment. Be able to cite the evidence of 4 out of 10,000 alpha particles were reflected / deflected as proof that the volume occupied by the nucleus is 1/100,000 of the volume of the rest of the atom.
Be able to diagram the number of protons, neutrons, and electrons in an atom or ion (charged atom) of a particular isotope. This is coved by the Atomic Structure worksheet and also the Atomic History / Isotopes Quiz given earlier in the unit of study. Be able to calculate the average atomic mass of an element when percent abundance and atomic mass of each isotope is given. The Isotopes and Average Atomic Mass worksheet covers this along with the Atomic History / Isotopes Quiz. Be able to calculate the percent abundances of an element when the atomic masses of the isotopes is given and the average atomic mass. You will need to use multiple equations (two) to solve for the multiple variables (two) of the percent abundances. You can use which ever method is most effective for you (substitution, elimination, matrices) to solve for the variables. The Isotopes of Pennium activity and Isotopes / % Abundance Problems worksheet cover this topic. Along with isotopes (which you will need to be able to define), you must also know how a mass spectrometer would be used to detect and quantify the different isotopes or chemical compounds in a sample. Remember, the particles must be charged the same (negative or positive) to have their path direction changed in the same way by a magnetic field. The separation occurs when the masses of the different isotopes / compounds dictate that they take different radii paths. The heavier particles will take the wider radius turn and the lighter particles will take the smaller radius turn. This is covered in the notes and in the Atomic History / Isotopes Quiz.
Know about radioactive decays (alpha, beta, gamma, neutrons, positrons) and how to balance the atomic numbers (bottom numbers) and atomic masses (top numbers) on each side of a nuclear decay reaction. This is covered in the nuclear radiation packet and the by the worksheet on the very back of that packet labeled "Nuclear Decay". Know how to designate a parent isotope and a daughter isotope. Know that a nucleus of a isotope is unstable because the ratio of protons and neutrons in the nucleus is too large and particles must be released from the nucleus to attain stability to the nucleus. Know about how nuclear decay of uranium in soil can lead to the formation of radon (Rn) gas that can enter a home through cracks in the foundation of a home. Know that the radon gas is a heavier than air gas, thus it will collect in the low point of a home, which is usually the basement. Know that radon gas can be breathed in and once in a persons lungs, can udergo a nuclear decay. Know the biological effects of radiation on tissues and DNA. This all can be found in the radiation packet.
Know the concept of half-life and how it can be utilized to determine the age of a material. Know that nuclear decays are random / spontaneous events. The reason that nuclear decays happen at a consistent rate is that the population is large enough to cause random events happen at a constant rate. Refer to the baby being born in Littleton in the next minute (maybe) versus a baby being born in the United States in the next minute (definite) example used in class. Know that a number of decays (y-axis) over time (x-axis) graph is exponential. The reason that the graph flattens out is the population of the parent isotopes has decreased, thus the instantaneous rate of decays goes down. The reason natural logs (ln) were used in class was to take the exponential graph of number of decays versus time and straighten it out to a linear relationship. You will not be asked to determine any values from a graph like what was done in class. That was merely to show you that the use of natural logs was necessary. You will be expected to isolate and solve for any variable in the general equation: ln[X] = -kt + ln[X]o. This is covered by the notes package on radiometric dating and the Half-Life / Radiometric Dating worksheet. Remember, if you are asked to solve for ln[X] or ln[X]o, you must find the value then find the inverse ln (e^x) of that value to find the true value. If percentages are used in a problem, the original amount (ln[X]o) is always 100%. You will be asked questions about dating the ash layer that was a focal point of the discussion of radiometric dating. Know that the ratio of unstable U-238 to the stable isotope of Pb-206 was central to dating the ash layer. You must also know the process of carbon-14 dating. Know that carbon-14 is created in the upper atosphere by neutrons from outerspace bombarding nitrogen-14 in the upper atmosphere. Know that the creating of carbon-14 and its demise to nitrogen-14 via beta decay both happen at the same rate, thus the percentage of carbon-14 in the environment stays constant. Know that when a living organism dies, it stops incorperating carbon-14 in its bio-mass. The level of carbon-14 in the bio-mass decreases from the point of death and the ratio of carbon-14 to the daughter isotope of nitrogen-14 will be what can be used to determine how long the organism has been dead. All concepts dealing with carbon-14 dating are presented in the radiometric dating notes packet.
Please do not let the length of this blog post be daunting. You probably know most of this material, I just want to make sure that you are not surprised by any material on the test. That is why the detail of this post is so involved. Study hard and see me outside of class if you have any questions.
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