Chapter 7 - Chapter 7: Electronic Structure of Atoms A....

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Chapter 7: Electronic Structure of Atoms A. Quantum Theory Electrons in atoms can have only certain discrete energies, referred to as energy states or energy levels. Normally, the electron is in the state of lowest energy called the ground state (n=1). By absorbing a certain definite amount of energy, the electron can move to a higher level, called an excited state (n=2,3. ..). When electrons return to lower energy levels, energy may be given off as light. The difference in energy between the levels can be deduced from the wavelength or frequency of the light. Postulates of the Quantum Theory 1. Atoms and molecules can only exist in certain states, characterized by definite amounts of energy. When an atom or molecule changes its state, it absorbs or emits an amount of energy just sufficient to bring it to another state. 2. When atoms or molecules absorb or emit light in moving from one energy state to another, the wavelengths ( ) of the light is related to the energies of the two states by the equation. E hi - E lo = (absorbed photon, higher energy state) ( E = E final - E initial = E hi - E lo ) E lo - E hi = - (emitted photon, lower energy state) hc = 1.196x10 5 3. The allowed energy states of atoms and molecules can be described by sets of numbers called quantum numbers. B.
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This note was uploaded on 12/03/2009 for the course CHM CHM140 taught by Professor Krish during the Spring '09 term at University of Toronto- Toronto.

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Chapter 7 - Chapter 7: Electronic Structure of Atoms A....

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