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EGN3365-2b

# EGN3365-2b - 1 Chapter 2 Atomic Structure and Interatomic...

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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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EGN3365-2b - 1 Chapter 2 Atomic Structure and Interatomic...

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