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Unformatted text preview: Crystals of Gallium 1 • At interactions between atoms are negligible
– Solids form because atoms have lower overall energy when they’re close together at low T • As the atoms approach each other, each exerts forces on the other – Attractive force, FA ; repulsive force, FR – Magnitude of force is a function of interatomic distance – The bond‐length corresponds to the distance at which the attractive and repulsive forces exactly balance.
2 • • FNET FA FR
– FNET 0 – The “sweet spot” – r0⋍0.3nm for most atoms
3 • Energy – minimum energy is called the bond energy, E0 energy that is required to completely separate two atoms
r r r E N FN dr FA dr FR dr E A E R – bond length: dE N 0 dr r0 4 •
– Bond energy – Bond length – curvature • • • chap 6 chap 19 5 6 •
– Ionic – Covalent – Metallic EA A r ER B r n • Coulombic force – attractive forces that by virtue of their positive and negative charge attract one another – Hydrogen ( Z1e)( Z 2 e) A – Van der Waals 4 0 – Dipole induced, permanent 7 • • • • • •
8 1. Two ions are separated by an infinite amount of space. When the two ions are brought close to one another, they begin to interact with attractive and repulsive forces. When in an equilibrium position, which of the following statements most accurately describes the “bond length.” i. ii. iii. iv. The bond length is the distance between the two ions where the net force is zero. The bond length is the distance between the two ions where the net force is maximum. The bond length is the distance between the two ions where the net energy is zero. The bond length is the distance between the two ions where the net energy is minimum. a i. and iii. b i. and iv. c ii. and iii. d ii. and iv. a b c d Hydrogen Bonding, Van der Waals Bonding, Metallic Bonding, Covalent Bonding Van der Waals Bonding, Hydrogen Bonding, Covalent Bonding, Metallic Bonding Van der Waals Bonding, Hydrogen Bonding, Metallic Bonding, Covalent Bonding Van der Waals Bonding, Covalent Bonding, Metallic Bonding, Hydrogen Bonding FAttraction 0.90eV .nm 2 r3 FRepulsion 5.9 10 5 eV .nm10 r 11 ...
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- Spring '10