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Eng 45 - Chapter 1 - Structure(19)

Eng 45 - Chapter 1 - Structure(19) - together and increases...

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Materials Science Fall, 2007 Page 18 distance is decreased further. Neglecting the effect of atom vibrations, the equilibrium separation of the atoms is r 0 , and the binding energy is the value of the potential, Ï(r 0 ), at the equilibrium separation. The bonding interaction between two atoms is reasonably well fit by the simple equation, Ï(r) = A r m - B r n 2.1 where Ï(r) is the potential energy of the bond as a function of the internuclear separation, r, A and B are constants, n is an exponent that governs the attractive, long-range interac- tion (its value depends on the specific bond type), and m (> n) is an exponent that governs the repulsive, short-range interaction. This function is called the Lennard-Jones potential , and has the shape shown in Fig. 2.1. The associated interatomic force, F = - dr = mA r m+1 - nB r n+1 2.2 vanishes in the limit of infinite separation, is attractive when the atoms are far apart, van- ishes at the equilibrium separation, r 0 , is repulsive when the atoms are very close
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Unformatted text preview: together, and increases without bound as r “ 0 so that the atoms cannot merge into one another. We shall find this simple representation of the binding potential useful at several points in the course to clarify the consequences of chemical binding. 2.3.2 The three mechanisms of chemical bonding -+ Ionic bond +-+-Dipole bond Shared Electron Bond covalent metallic Fig. 2.2: The three basic mechanisms of interatomic bonding While all interatomic bonding is due to electrostatic interactions between the elec-trons and the nuclei, it is useful to distinguish three basic mechanisms (Fig. 2.2). These correspond to the three different ways in which the electron clouds on adjacent atoms can Thank you for evaluating AnyBizSoft PDF Splitter. A watermark is added at the end of each output PDF file. To remove the watermark, you need to purchase the software from http://www.anypdftools.com/buy/buy-pdf-splitter.html...
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Eng 45 - Chapter 1 - Structure(19) - together and increases...

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