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Unformatted text preview: AP Chemistry AP Chemistry AP Chemistry AP Chemistry Atomic Theory Outline Atomic Theory Outline Atomic Theory Outline Atomic Theory Outline (APatomicoutline.doc) A wave can be considered a periodic disturbance in space that carries energy. Some properties of waves are: Wavelength ( (lambda)) = The distance between two consecutive identical points on a wave (often measured from crest to crest). Wavelengths are often expressed in nanometers, but should be converted to meters before being used in an equation. Amplitude (A) = The distance to the maximum displacement from equilibrium Frequency ( (nu) or sometimes f) = The number of wave cycles that occur each second. Frequency is normally measured in hertz (Hz). It may also be seen as cycles/sec, 1/s or just s-1 Period (T) = The time for one wave cycle ( = 1/ ) Velocity (v or sometimes u) = The speed of the wave through space. Electromagnetic waves always travel at a constant rate through the vacuum of space so its velocity is given the constant c , and is 3.0x10 8 m/s . For an electromagnetic wave, the product of the wavelength and the frequency always equals the speed of light. c = Unlike a mechanical wave whose energy is carried on the amplitude of the wave, the energy of an electromagnetic wave is carried on its frequency. The different types of electromagnetic waves from lowest energy (i.e. lowest frequency and longest wavelength) to highest are: Radio waves, microwaves, infrared, visible, ultraviolet, X-rays, gamma rays The visible spectrum runs from about 400nm (blue-violet) to 700nm (red). All of these waves stem from the same source, namely the transition of an electron from a more energetic position around the nucleus of an atom to a lower energy position. The model of the atom towards the end of the 1800's was that of the electron behaving like a planet going around the sun, represented by the nucleus. The attraction between the positive nucleus and negative electron was counterbalanced by the angular acceleration of the electron around the nucleus. The energy of the wave is determined by the difference in energy between the positions. In the latter part of the nineteenth century, scientists were confused by several aspects of light. 1. Since accelerating charged particles emit energy, they didn't know why electrons didn't spiral into the nucleus. 2. Why rarefied, energized gases only gave off certain frequencies of light instead of a continuous spectrum, since all electron "jumps" should be possible. 3. Why equations based on current knowledge of physics at the time was only able to partially describe the energy emitted at different wavelengths by an object. Some equations described the shorter wavelength region, others the longer wavelengths....
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This note was uploaded on 12/07/2011 for the course CHEM 100 taught by Professor Feebeck during the Fall '10 term at Purdue University-West Lafayette.
- Fall '10