Lecture 3 - Bonding MEEN 222-502 Yeon Seok Kim (2008)* *...

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1 MEEN 222-502 Yeon Seok Kim (2008)* * Some information has taken from Callister’s Online Instructor Resource Bonding MEEN 222-502 Yeon Seok Kim (2008)* * Some information has taken from Callister’s Online Instructor Resource Learning Objectives: Learning Objectives: • Understand attractive, repulsive and net forces • Understand the relationship between bonding forces and energies • Determine equilibrium spacing and bonding energy between atoms • Link between bonding and bulk properties • Identify primary and secondary bonding mechanisms
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2 MEEN 222-502 Yeon Seok Kim (2008)* * Some information has taken from Callister’s Online Instructor Resource Bonding Forces and Energies Bonding Forces and Energies • To understand many physical properties of matter it is essential to understand the interatomic forces that bind the atoms together • The forces between atoms depend on the distance of separation – At large distances interatomic forces are negligible • The net force results from attractive and repulsive forces: • At equilibrium, repulsive and attractive forces balance each other. . R A N F F F + = MEEN 222-502 Yeon Seok Kim (2008)* * Some information has taken from Callister’s Online Instructor Resource Attractive Attractive vs vs Repulsive Forces Repulsive Forces • Attractive forces: – Depend on particular type of bonding • Ionic, covalent, metallic, van der waals , etc – The stronger the interaction, the stronger the bonding force • Repulsive forces: – As interatomic distance decreases, the outer electron shells in atoms begin to overlap • Electrostatic and Pauli repulsion • Equilibrium spacing: – Achieved when forces cancel out (remember statics): 0 = + R A F F
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3 MEEN 222-502 Yeon Seok Kim (2008)* * Some information has taken from Callister’s Online Instructor Resource Equilibrium distance Equilibrium distance Think of a mass-spring system: What is the force equation for the spring? – F = K(x-x 0 ) •W h e n –x > x 0 • Positive force tries to bring masses closer to each other < x 0 • Negative force tries to separate masses = x 0 • Masses are separated by equilibrium distance r MEEN 222-502 Yeon Seok Kim (2008)* * Some information has taken from Callister’s Online Instructor Resource Attractive Attractive vs vs Repulsive Forces Repulsive Forces • What is the equilibrium separation, r0? – Suppose that: () 1 R 2 F r A + = = n A r nB F ( ) n nB A r = 1 / 1 0 r 0 F A +F R
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4 MEEN 222-502 Yeon Seok Kim (2008)* * Some information has taken from Callister’s Online Instructor Resource Slope of Force and Stiffness of Material • The slope of the Force vs distance curve is related to the stiffness of a material – The greater the slope, the more difficult it is to take the atoms apart – A smaller slope indicates that the bond can be stretched easily – In solids, this slope is known as the Bulk Modulus MEEN 222-502 Yeon Seok Kim (2008)* * Some information has taken from Callister’s Online Instructor Resource Bonding Energies Bonding Energies • How are bonding energies related to forces?
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Lecture 3 - Bonding MEEN 222-502 Yeon Seok Kim (2008)* *...

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