Intermolecular Forces and Liquids and Solids · Intermolecular Forces Hydrogen Bond 11.2 The...
Transcript of Intermolecular Forces and Liquids and Solids · Intermolecular Forces Hydrogen Bond 11.2 The...
Chemistry for Engineers, SCS126
Intermolecular Forces andLiquids and Solids
Chapter 11
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Reading Assignments:
Chapter 11 inR. Chang, Chemistry, 9th Ed., McGraw-Hill, 2006. or previous editions.
Or related topics in other textbooks.
Consultation outside lecture room:Office Hours:
Tuesday & Thursday 10 AM -12 noon, Wednesday 1-4 PM
@Room 313-3 or by appointment
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Intermolecular Forces
11.2
molecular forces are attractive forces between molecules.
molecular 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 intramolecularforces.
“Measure” of intermolecular forceboiling pointmelting point
∆Hvap
∆Hfus
∆Hsub Chemistry for Engineers, SCS126
Intermolecular Forces
Dipole-Dipole Forces
Attractive forces between
Orientation of Polar Molecules in a Solid
11.2
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Intermolecular Forces
Ion-Dipole Forces
Attractive forces between an ion and a polar molecule
11.2 Chemistry for Engineers, SCS126 11.2
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Intermolecular ForcesDispersion Forces
Attractive forces that arise as a result of dipoles induced in atoms or molecules
11.2
ion-induced dipole interaction
dipole-induced dipole interaction
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Induced Dipoles Interacting With Each Other
11.2
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Intermolecular ForcesDispersion Forces Continued
11.2
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.
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SO O
What type(s) of intermolecular forces exist between each of the following molecules?
HBr
CH4
SO2
11.2
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Intermolecular ForcesHydrogen Bond
11.2
The hydrogen bond is a special dipole-dipole interaction between they 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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Hydrogen Bond
11.2
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Why is the hydrogen bond considered a “special” dipole-dipole interaction?
Decreasing molar massDecreasing boiling point
11.2 Chemistry for Engineers, SCS126
Properties of Liquids
Surface tension is the amount of energy required to stretch or increase the surface of a liquid by a unit area.
Strong intermolecular
forces
11.3
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Properties of Liquids
Cohesion is the intermolecular attraction between like molecules
11.3
Adhesion is an attraction between unlike molecules
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Properties of Liquids
Viscosity is a measure of a fluid’s resistance to flow.
11.3
Strong intermolecular
forces
High viscosity
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Maximum Density40C
Ice is less dense than water
Density of Water
11.3
Water is a Unique Substance
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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 11.4
At lattice points:
• Atoms
• Molecules
• Ions
Chemistry for Engineers, SCS126 11.4 Chemistry for Engineers, SCS126 11.4
Chemistry for Engineers, SCS126 11.4 Chemistry for Engineers, SCS126 11.4
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Shared by 8unit cells
Shared by 2unit cells
11.4 Chemistry for Engineers, SCS126 11.4
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)
Chemistry for Engineers, SCS126 11.4 Chemistry for Engineers, SCS126
When silver crystallizes, it forms face-centered cubic cells. The unit cell edge length is 409 pm. Calculate the density of silver.
d = mV V = a3
4 atoms/unit cell in a face-centered cubic cell
m = 4 Ag atoms 107.9 gmole Ag
x1 mole Ag
6.022 x 1023 atomsx = 7.17 x 10-22 g
d = mV
7.17 x 10-22 g6.83 x 10-23 cm3=
11.4
Chemistry for Engineers, SCS126 11.5 Chemistry for Engineers, SCS126Extra distance = BC + CD = (Bragg Equation)
11.5
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X rays of wavelength 0.154 nm are diffracted from a crystal at an angle of 14.170. Assuming that n = 1, what is the distance (in pm) between layers in the crystal?
nλ = 2d sin θ n = 1 θ = 14.170 λ = 0.154 nm = 154 pm
d =nλ
2sinθ=
1 x 154 pm2 x sin14.17
11.5 Chemistry for Engineers, SCS126
Types of CrystalsIonic Crystals• Lattice points occupied by cations and anions• Held together by electrostatic attraction• Hard, brittle, high melting point• Poor conductor of heat and electricity
CsCl ZnS CaF211.6
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Types of CrystalsCovalent Crystals• Lattice points occupied by atoms• Held together by covalent bonds• Hard, high melting point• Poor conductor of heat and electricity
11.6diamond graphite
carbonatoms
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Fullerenes, “Buckyballs”• Buckminsterfullerene ( C60 )
– sp2 hybridized and has bonds to 3 other carbons
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Carbon nanotube• Nano wire• Molecular cage
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Types of CrystalsMolecular Crystals• Lattice points occupied by molecules• Held together by intermolecular forces• Soft, low melting point• Poor conductor of heat and electricity
11.6
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Types of CrystalsMetallic 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
11.6
Cross Section of a Metallic Crystalnucleus &
inner shell e-
mobile “sea”of e-
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Types of Crystals
11.6
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An amorphous solid does not possess a well-defined arrangement and long-range molecular order.
A glass is an optically transparent fusion product of inorganic materials that has cooled to a rigid state without crystallizing
11.7 Chemistry for Engineers, SCS126
Chemistry In Action: High-Temperature Superconductors