EGN3365-2b - 1/14/2011 1 Chapter 2. Atomic Structure and...

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Unformatted text preview: 1/14/2011 1 Chapter 2. Atomic Structure and Interatomic Bonding Interatomic Bonding Bonding forces and energies Primary interatomic bonds Secondary bonding Molecules Bonding Forces and Energies Considering the interaction between two isolated atoms as they are brought into close proximity from an infinite separation. At larger distances, the interactions are negligible. As the atoms approach, each exerts forces on the other. Attractive Repulsive Ultimately, the outer electron shells of the two atoms begin to overlap, and a strong repulsive force comes into play. 1/14/2011 2 Bonding Models Bonding holds atoms together to form solids materials In solids, atoms are held at preferred distances from each other (equilibrium distances) Distances larger or smaller than equilibrium distances are not preferred. Equilibrium spacing r is approximately 0.3nm Consequently, as atomic bonds are stretched, atoms tend to attract each other, and as the bonds are compressed, atoms repel each other. Simple bonding models assume that the total bonding results from the sum of two forces: an attractive force (F A ) and a repulsive (F R ). The repulsive force dominates at small distances, and the attractive force dominates at larger distances. At equilibrium they are just equal. R A N F F F + = the net force It is convenient to work with energy than forces. Bonding energy (also called interaction energy or potential energy) between two isolated atoms at separation r is related to the force by The total energy has a minimum at the point of equilibrium separation. Bonding energy E corresponds to the energy at r o the energy that would be required to separate these two atoms to an infinite separation. Interpretation: holding one atom at the origin, a second atom would repel that atom at separation r < r o and attract it when r o < r ....
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This note was uploaded on 12/03/2011 for the course EGN 3365 taught by Professor Jiuhuachen during the Fall '09 term at FIU.

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EGN3365-2b - 1/14/2011 1 Chapter 2. Atomic Structure and...

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