Chapter 7

# Chapter 7 - Quantum Mechanical model of the atom: Classical...

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Unformatted text preview: Quantum Mechanical model of the atom: Classical mechanics : The laws of physics, following the work of Isaac Newton,depend on mass, velocity and force. These laws deal with Kinetic energy of motion, potential energy of interaction between particles or with external fields. From a knowledge of current position, velocity and forces between particles, classical mechanics will allow you to predict the future position of a particle at a given time. These laws are applicable to macroscopic particles, such as planets, and objects encountered in day to day life. On the other hand, the behavior of microscopic particles or elementary particles such as electrons cannot be fully explained using classical mechanics. At such microscopic level a particle can exhibit the properties of a wave. Wave nature of light : A periodic oscillatory variation of property with time is a wave. The properties of wave are described by amplitude, wavelength and frequency. The height of the wave is called amplitude . Two identical points in a wave constitute one cycle. For example, two consecutive crest points, two consecutive trough points, or three consecutive zero points constitute one cycle . If an observer stands at one point and watches the wave pass by, the number of waves or cycles passed in a given second is called frequency, (in units of Hertz, Hz= cycles.s- 1 ). If a wave is held stationary and the distance between two crests or troughs of that wave is measured that distance is called wavelength and represented by symbol, , expressed as m.cycle-1 or simply as m). The product of wavelength and frequency of a wave is equal to the speed, c, of that wave. s m s cycle cycle m c = = = It has been demonstrated by James Maxwell that light is electromagnetic radiation and light wave is called electromagnetic wave . A electromagnetic wave consists of electric and magnetic fields, oscillating perpendicular to each other, with amplitudes E max and B max respectively. The wavelength or frequency of light wave determines the properties of that light wave. For example, the violet, indigo, blue, green, yellow, orange and red (VIBGYOR) colors of visible light that we can see with naked eye represent different electromagnetic waves with different wavelengths. The different ranges of electromagnetic wavelengths constitute different portions of electromagnetic spectrum (see the picture below). In the picture given below different portions of electromagnetic spectrum and their names are given. Name wavelength range -rays: ~10-16-10-12 m X-rays: ~10-12-10-8 m UV rays: ~10-8-10-6 m Visible: ~4x10-7 7x10-7 m Infrared: ~ 10-6-10-3 m Microwave:~ 10-3-10 0 m (or radar) FM,TV : ~ 1-100 m AM: ~10 3-10 4 m Conversion from wavelength to frequency : Velocity of light (irrespective of the nature of light) in vacuum is constant, 2.99x10 8 m.s-1 . Therefore, wavelength and frequency of a light component are related through the relation, c = Name wavelength range Frequency(=c/...
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## This note was uploaded on 02/27/2009 for the course CHEM 102a taught by Professor Hanusa during the Fall '06 term at Vanderbilt.

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Chapter 7 - Quantum Mechanical model of the atom: Classical...

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