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The Development of a New Atomic Model Chapter 4 Section 1 TEKS 2A, 2D, 2E; 3A, 3C, 3E; 5A-B, 6A 4-1 Objectives Explain the mathematical relationship among the speed, wavelength and frequency of electromagnetic radiation. Discuss the dual wave/particle nature of light. Discuss the significance of the photoelectric effect and the line-emission spectrum of hydrogen to the development of the atomic model. Diagram and describe the Bohr model of the hydrogen atom. Super Fun Chemistry Math! All forms of electromagnetic radiation move at a constant speed of 3.0 X 108 m/s (yeah, that’s the speed of light c). A wavelength λ is the distance between corresponding points on adjacent waves. Frequency f is the number of waves that pass a given point in one second. c = λf Remember E=mc2? That’s the same c. Waves of Light Visible light is a form of electromagnetic radiation a form of energy that exhibits wavelike behavior as it travels through space. Other kinds of electromagnetic radiation include: X-rays, ultraviolet and infrared light, microwaves and radio waves. These waves have different wavelength, frequency, and energy limits. BRAIN WAVES are also a form of EMR. Waves of Light Radio waves, visible light, X-rays, and all the other parts of the electromagnetic spectrum are fundamentally the same thing, electromagnetic radiation. Waves of Light Refer to Figure 4-1 on page 92 in your textbook for specific wavelengths of the electromagnetic spectrum. What wavelengths in the spectrum are visible to the human eye? Visible light is from ______ to ______. Waves of Light Why do we have to go to space to see the complete electromagnetic spectrum? Waves of Light Electric and magnetic fields oscillate together but perpendicular to each other and the electromagnetic wave moves in a direction perpendicular to both of the fields. Particles of light A little bit of history… The photoelectric effect refers to the emission of electrons from a metal when light shines on the metal. Check out a cathode ray tube in Figure 4-3 on page 93. Light was already known to be a form of energy, but scientists couldn’t explain why light had to be of a minimum frequency for the photoelectric effect to occur. Particles of light A little more history… 1900, German physicist Max Planck studying the emission of light from hot objects figured it out… A quantum is the minimum quantity of energy that can be lost or gained by an atom for the photoelectric effect to occur. Planck’s Constant: h = 6.626 X 10-34 J*s E=hf Energy of a quantum of radiation = (h) * frequency of radiation emitted Particles of light And yet more history… 1905, Albert Einstein expanded on Planck’s theory by introducing the notion that EMR has a dual nature: both a wave and a particle. A photon is a particle of electromagnetic radiation having zero mass and carrying a quantum of energy. In the formula Ephoton=hf, Einstein explained the photoelectric effect. A photon particle with sufficient energy strikes the electrons. Particles of light And yet more history… WHOA NELLY! I bet that this work led to Einstein’s development of the theory of special relativity! E=mc2 Okay… enough already! My brainwaves are oscillating at a low frequency For classwork, due TODAY, October 22, a few more questions… Okay… enough already! My brainwaves are oscillating at a low frequency What two objects have we studied that have a cathode and an anode and are used to study electron behaviors? (refer to p.70 and 93) Which wavelengths in the Electromagnetic Spectrum make up “visible light?” (p 92) What was the precursor to Einstein’s theory of special relativity, E=mc2, that disproved one part of Dalton’s Atomic Theory? (photons’ mass) And just for joy In the electromagnetic spectrum, what is the wavelength and frequency of your favorite color?
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