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Transcript
Atomic Scientists Unit II, LT # 1 Chapter 3 Scientist’s and Their Contribution to Our Current Atomic Theory Directions: Based off of the presentations that each group gave answer the following questions about each of the following scientists and their contribution to the modern atomic theory. Democritus What was the term that he used for the tiny particles that everything is composed of? Atomos What were the two main ideas of his theory? 1. All things are composed of atoms. 2. Atoms cannot be broken down into simpler things. John Dalton What are the four main postulates of Dalton’s Atomic Theory? 1. All matter is composed of tiny particles. 2. Atoms are indestructible and unchangeable. 3. When elements react, their atoms combine in simple, whole-number ratios. 4. When elements react, their atoms sometimes combine in more than one simple, wholenumber ratio. Draw a picture of Dalton’s atomic model. When did John Dalton present his findings/discoveries about the atom? 1805 Dmitri Mendeleev What was his main contribution to science? The father of the modern periodic table. J.J. Thomson What atomic particle did J.J. Thomson investigate? The electron. Describe Thomson’s experiment. (i.e. What did he used to investigate the answer to number 5?) Thomson used electrical and magnetic fields to deflect cathode rays. He discovered that the cathode rays were deflected towards the positively charged plates and concluded that the cathode rays must have negative charged particles. What was Thomson’s discovery and when did he make it? Thomson discovered the mass to charge ration of the electron and is credited with the discovery of the electron. What luxury item today is associated with Thomson? Television set Robert Millikan Whose work did Millikan expand upon? Thomson Describe Millikan’s experiment. An atomizer sprayed a fine mist of oil droplets into a chamber. Some of these tiny droplets fell through a hole in the upper floor. Millikan first let them fall until they reached terminal velocity. Using the microscope, he measured their terminal velocity, and by use of a formula, calculated the mass of each oil drop. Next, Millikan applied a charge to the falling drops by illuminating the bottom chamber with x-rays. This caused the air to become ionized, and electrons to attach themselves to the oil drops. By attaching a battery to the plates above and below this bottom chamber, he was able to apply an electric voltage. The electric field produced in the bottom chamber by this voltage would act on the charged oil drops; if the voltage was just right, the electromagnetic force would just balance the force of gravity on a drop, and the drop would hang suspended in mid-air. What did Millikan discover during his experiment? Millikan was able to calculate the exact charge of the electron. How did Thomson’s and Millikan’s experiments modify Dalton’s Atomic Model? (What did their model of the atom look like?) Now the atom has negatively charged particles in it. Henri Becquerel Why is his (and the Curies) discovery of radioactivity vital to the development of the atomic theory? Without the discovery of radioactivity Ernest Rutherford could not perform his gold foil experiment. Ernest Rutherford Describe in what Rutherford did in his experiment. This experiment involved the firing of radioactive particles through minutely thin metal foils (notably gold) and detecting them using screens coated with zinc sulfide (a scintillator). What element did Rutherford primarily use to perform his experiment? Gold What was Rutherford’s discovery and how did it contribute to our current view of the atom? Rutherford discovered that atoms are comprised mostly of empty space and that at an atom’s center is a very small, dense positive structure (nucleus). Draw a picture of the Rutherfordian model of the atom? Henry Moseley If Moseley would have lived would our findings about the atom and its’ structure be different? Not really, his contributions would have been the same and further contributions were deterred by lack of technology.