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1
Intermolecular Forces and
Bonding in Solids
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3 States
Solid state - ice
Liquid state - water
Different States of Matter
Gas state - water vapor
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“Measure” of intermolecular force
boiling point
melting point
Hvap
Hfus
Hsub
Intermolecular Forces
Intermolecular forces are forces between molecules.
Intramolecular forces hold atoms together in a molecule.
Intermolecular vs Intramolecular
• 41 kJ to vaporize 1 mole of water (inter)
• 930 kJ to break all O-H bonds in 1 mole of water (intra)
Generally, intermolecular forces are much weaker than intramolecular forces.
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Intermolecular Forces
Dipole-Dipole Forces: Attractive and repulsive forces between polar molecules
solid
liquid
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Intermolecular ForcesHydrogen Bond: a special dipole-dipole interaction between the hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom.
A H…B A H…Aor
A & B are N, O, or F
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Dispersion Forces: Attractive forces that arise as a result of temporary dipoles induced in atoms or molecules
Intermolecular Forces
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Dispersion Forces among Nonpolar Molecules
separated Cl2
molecules
instantaneous dipoles
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Polarizability is the ease with which the electron distribution in the atom or molecule can be distorted.
Polarizability increases with:
• greater number of electrons
• more diffuse electron cloud
Dispersion forces usually increase with molar mass.
Intermolecular Forces
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SO
O
What type(s) of intermolecular forces exist between each of the following molecules?
HFHF is a polar molecule: dipole-dipole forces. Hydrogen is bounded to F. Hydrogen bonds exist. There are also dispersion forces between HBr molecules.
CH4
CH4 is nonpolar: dispersion forces.
SO2
SO2 is a polar molecule: dipole-dipole forces. There are also dispersion forces between SO2 molecules.
Intermolecular Forces
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A crystalline solid possesses rigid and long-range order. In a crystalline solid, atoms, molecules or ions occupy specific (predictable) positions.
An amorphous solid does not possess a well-defined arrangement and long-range molecular order.
A unit cell is the basic repeating structural unit of a crystalline solid.
Unit Cell
latticepoint
Unit cells in 3 dimensions
Structures and Types of Solids
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Seven Types of Unit Cells
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1 atom/unit cell
(8 x 1/8 = 1)
2 atoms/unit cell
(8 x 1/8 + 1 = 2)
4 atoms/unit cell
(8 x 1/8 + 6 x 1/2 = 4)
Three Types of Cubic Cells
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The Striking Beauty of Crystalline Solids
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Three Types of Crystalline Solids
atomic solid ionic solid molecular solid
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Types and Properties of Solids
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Metallic Crystals
• Lattice points occupied by metal atoms• Held together by metallic bonds• Soft to hard, low to high melting point• Good conductors of heat and electricity
nucleus &inner shell e-
mobile “sea”of e-
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MO Energy Levels as a Function of the # of AO
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The band of MOs in lithium metal
ConductionBand
ValenceBand
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Covalent Crystals
• Lattice points occupied by atoms• Held together by covalent bonds• Hard, high melting point• Poor conductor of heat and electricity
diamond graphite
carbonatoms
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Graphite Consists of Layers of Carbon Atoms
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conductor
Electrical Conductivity in Graphite
sp2 hybridization Delocalized orbitals
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insulator
Electrical Conductivity in Diamond
sp3 hybridization localized orbitals
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Conductor, Semiconductor, and Insulator
conductor
semiconductor
insulator
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n-type p-type
Doped Semiconductors
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Chemistry In Action: High-Temperature Superconductors
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Acknowledgment
Some images, animation, and material have been taken from the following sources:
Chemistry, Zumdahl, Steven S.; Zumdahl, Susan A.; Houghton Mifflin Co., 6th Ed., 2003;
supplements for the instructor
General Chemistry: The Essential Concepts, Chang, Raymon; McGraw-Hill Co. Inc., 4th
Ed., 2005; supplements for the instructor
Principles of General Chemistry, Silberberg, Martin; McGraw-Hill Co. Inc., 1st Ed., 2006;
supplements for the instructor
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