CEM 141 Chapter Notes - Chapter 2: Photon, Ion, Effective Nuclear Charge

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12 Sep 2018

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Most scientists had come to accept a wave model for light because it better explained behaviors such as interference and diffraction. Phenomena that gave rise to patterns waves pass through or around objects of similar size to the wave itself. James clerk maxwell developed the electromagnetic theory of light. Visible light and other forms of radiation were viewed in terms of perpendicular electric and magnetic fields. A light wave can be described by defining frequency (v) and its wavelength ( ) Frequency times equals velocity of a wave. An object was heated to a particular temperature emitted radiation. He studied how the color of light emitted changed as a function of. Developed the idea that matter absorbs and emits energy in an object"s temperature. The physics that uses quanta is known as quantum mechanics. As frequency of light increased his measurements diverged more and more from the prediction of the current wave-based theory.

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LIGHT LAB SPRING 2018 CHEM 1430 Ill. Quantization of Electromagnetic Radiation In 1894, the German physidist, Max Plank, was working for a utility company to maximize visible light output from incandescent lamps using minimum power. Based on theoretical considerations, Planck postulated that electromagnetic energy could only be emitted at discrete values, rather than the continuum of predicted by classical physics, as multiples of the frequency of the radiation. Planck's Postulate took the mathematical form: EÂ·hv where the energy emitted, in Joules, is the product of a constant, h, known as Planck's Constant, and the frequency of the radiation, v. Planck's Postulate was experimentally verified and h found to have the value of 6.626 x 1034 Js(Joule seconds). The idea that electromagnetic radiation energy had specific frequency dependent energy was termed a "quantum of action," a distressing finding for the dlassically trained Planck. Despite his objections, Planck adopted this quantization of energy as a last resort to reconcile experiment with theory. This discovery set the stage for the early understanding of atomic structure, led to the term "photon" to describe the packet of energy carried by light waves, led to an understanding of the photoelectric effect, eventually leading to the development of general quantum theory Planck's Relationship, in combination with the tight equation, c the energy of a photon from frequency or wavelength. Î» w, allow expressions to be written to calculate ACTIVITY 4: QUANTIZATION OF THE ENERGY OF RADIATION To practice cakculations with Planck's Relationship, complete the following table, showing work with units in the right mest column, Convert given frequency to energy or given wavelength to energy. Take the value for Planck's Constant, h, to be 6.626 x 10"Js, show a calculation string include dimensions, reporting the final value to the proper number of significant figures Spectral Region Wavelength Frequency Energy in J/photon Show Calculation String Î» in meters v in s or cps X-ray 6.0 x 10"m Blue light 4.5 x 10m Infrared 4.1 x 10" cps Microwave 7.3 x 101 cps Radio Wave 3.0x 10 m IV. Bohr's Quantum Model for the Hydrogen Atom Ernest Rutherford's Gold Foil Experiment of 1911 demonstrated the nuclear structure of the atom. Questions remained as to how electrons were arranged in the atom. The most common belief called for the negatively charged the late 19h century recognized a particle (an electron) traveling around a body (the positively charged nucleus) would continuously radiate energy, slowing over time, eventually falling into the nucleus. Matter would collapse. Page 8 of 12

CEM 141 Chapter Notes - Chapter 2: Photon, Ion, Effective Nuclear Charge

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