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UT CH 301 - Exam 1 Study Guide

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CH 301 1st Edition Exam # 1 Study Guide Lectures: 1 - 6 Lecture 1 (January 20) Atomic Theory I. The Rutherford Atom a. The model consisted of a central core containing most of the mass and half the charge of the atom, surrounded by a cloud of electrons. i. Major limitations: 1. Didn’t explain why elements have different properties 2. Didn’t explain how chemical bonding occurred 3. Didn’t explain stoichiometry 4. Orbiting electrons should have radiated energy & slowly plummeted to the core 5. Didn’t explain why atoms of different elements give off light of characteristic colors → atomic emission. II. Wave Properties a. Wavelength λ (Lambda): distance between two consecutive peaks in a wave, measured in meters. b. Frequency ν (Nu): The number of waves that pass a given point in space in a second, measured in units of inverse time 1/sec or Hertz (Hz). i. λν = constant → They share an inverse relationship. ii. λ(m) ν(s-1) = constant (ms-1) or speed. III. Electromagnetic Radiation - Light a. A form of radiant energy b. Travels in waves c. Types: i. Radio Waves ii. TV waves iii. Radar waves iv. Infrared v. Visible Light vi. Ultraviolet Light vii. X-rays viii. Short waves ix. Microwaves x. Gamma Rays Lecture 2 (January 22)I. EM Radiation - Light a. Short wavelength → high frequency → high energy b. Long wavelength → low frequency → low energy c. Visible light spectrum : 780nm to 390 nm 1. ROY G BIV: red, orange, yellow, green, blue, indigo, purple 2. Red is longest wavelength and purple is shortest wavelength in visible light spectrum d. The speed of light, c, is a constant in any specific medium. For light passing through a vacuum (meaning space with no atoms or molecules in it): c = 2.9979249 x 108  ms-1 II. Blackbody Radiation a. The phenomenon of color change with temperature change b. Studied by Max Planck. 1. A theoretically ideal black body radiator would be an object that absorbs all wavelengths of light and reflects nothing, therefore is appears black. Heating the object would result in radiation being emitted that is independent of what it’s made of, and its surroundings. Color change would only be dependent on temperature. c. Experimental observations found that as temperature increases, intensity (brightness) of the light increases and peak wavelength of the light decreases. d. Classical physics predicted that as temperature increased in an ideal black body, intensity would increase and wavelength would decrease indefinitely. Meaning there would be infinite intensity at 0nm. However, this theory did not math the experimental observation. This is called the Ultraviolet Catastrophe. 1. Planck was able to develop a theory and equation that accurately predicted Blackbody intensity: ● ΔE = nhv → delta E is the energy change of the system, n is an integer, v is frequency, and h is now called Planck’s constant → h = 6.626 x 10-34 J s III. Photo Electric Effect a. Initial Observations: 1. There is a threshold frequency for light, below which no electrons were emitted. 2. The threshold frequency was independent of light intensity 3. Threshold frequency varies for different photocathode metals. 4. Above the threshold frequency, # of electrons increases as light intensity increases b. Albert Einstein’s explanation:1. Electromagnetic radiation can be thought of as a stream of particles, each with a quantized amount of energy. Light, which we normally thought of as a wave, also acts as if it is made up of particles, which he called photons. The energy of which is described by: E = hv = hc/λ Lecture 3 (January 27) I. Particle Nature of Light a. Light can behave as particles (photons), each with quantized energy II. Wave Nature of Light a. Interference: when two sets of ripples run into each other. b. Constructive interference: the two waves join and the new wave has an increased amplitude c. Destructive interference: the two waves join and the new wave has a reduce amplitude III. Wave particle duality: the properties of light can only be explained if you attribute both wave-like and particle-like behavior to electromagnetic radiation. IV. Atomic Spectroscopy: Newton used a prism to disperse the wavelengths of sunlight. Using this method, you will see light at only specific wavelengths. a. Emission spectrum: spectrum of frequencies of electromagnetic radiation emitted due to an atom or molecule making a transition from a high energy state to a lower energy state. b. Absorption spectrum: radiation absorbed by a material at certain frequencies. c. Lines on the emission spectrum correspond to absence of color on the absorption spectrum V. Rydberg Equation a. An empirical formula that fits the observed lines in the hydrogen emission spectrum, but has not theoretical basis. 1.1/λ = R (1/n12 - 1/n22) where R= 1.097 x 107 m-1 2.To find frequency: 3.To find Energy:Lecture 4 (January 29) VI. Bohr Atom: atomic model created by Neils Bohr using Planck and Einstein’s new ideas. First to explain both atomic emission and spectra, and Rydberg’s empirical formula. VII. Bohr described the electron of a Hydrogen atom orbiting the nucleus, similar to the Rutherford atom but, with changes: a. The electron’s energy is quantized b. Electrons can only occupy specific orbitals c. Each orbit corresponds to a different electron energy d. Lower energy orbitals are smaller in diameter. e. When an electron moves from one orbital to another, it makes a “transition”. f. To drop from a higher energy orbital to a lower energy orbital, an electron has to lose energy. It does so by emitting a quantized amount of energy (photon). g. The lowest possible electron energy lever (n=1) is the closest to the nucleus. The electron is the happiest there, it’s called the ground state. h. The higher energy states are called excited states. VIII. Ionization Energy a. Energy required for an electron to go from ground state to excited state. IX. Wave Mechanicsa. Standing wave: a wave that appears to be stationary. One of the common ways to create a standing wave is from interference between waves moving in opposite directions. Lecture 5 (January 31) I. Heisenberg Uncertainty Principle a. Shows that there is fundamental limit to how certain one can be of knowing certain properties. The size of uncertainty in


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