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AP Notes Chapter 12 & 13 Intermolecular Forces, Liquids and Solids

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1. Ion - Ion

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Dissociation Energy Opposite of Lattice Energy MX (s) M + (g) + X - (g)

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1. Ion - Ion 2. Ion - Permanent Dipole

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Hydrated Ions A particle that is only weakly polar but is much larger than ion alone The number of waters of hydration depends on size of ion and strength of charge to be stabilized (typically less than 5)

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1. Ion - Ion 2. Ion - Permanent Dipole 3. Dipole - Dipole

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Occurs between molecules with permanent dipoles (SO 2, CHCl 3, etc)

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Hydrogen-Bonding Relatively strong attraction between a hydrogen atom in one molecule and a highly electronegative atom (F, O, N) in a different molecule

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Hydrogen-Bonding Strong enough to produce a phase change in a compound that should be more random at that temperature (about 1.5 kJ)

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Dimer of Acetic Acid

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Hydrogen-Bonding How and why of bonding is not clear - most likely due to strong attraction between e - cloud of the highly EN atom and the nucleus of the H atom

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QUESTION Is the hydrogen bond a true chemical bond or is it just a very strong electrostatic attraction?

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1. Ion - Ion 2. Ion - Dipole 3. Dipole – Dipole 4. Dipole-Induced Dipole

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1. Ion - Ion 2. Ion - Dipole 3. Dipole – Dipole 4. Dipole-Induced Dipole 5. Dispersion Forces

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Dispersion Forces Process of distorting an electron cloud by electrostatic forces of attraction and repulsion. Weakest of the intermolecular forces.

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Non-polar molecules Momentary attractions & repulsions Temporary dipoles established

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Dispersion forces also called van der Waals forces

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LIQUIDS & SOLIDS

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Cohesive Forces various intermolecular forces holding a liquid together

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Vaporization Process in which a substance in the liquid state becomes a gas. Process in which a substance in the liquid state becomes a gas. Vaporization requires energy since it involves separation of particles that are attracted to one another. Vaporization requires energy since it involves separation of particles that are attracted to one another.

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Standard Molar Enthalpy of Vaporization, Hº vap Energy required to convert one mole of liquid to one mole of the corresponding gas at the BP. Energy required to convert one mole of liquid to one mole of the corresponding gas at the BP. Always endothermic, H vap is positive. Always endothermic, H vap is positive. Liquids having greater attractive forces have higher H vap Liquids having greater attractive forces have higher H vap

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Opposite of Evaporation Condensation -- Exothermic Condensation

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Viscosity a measure of the resistance to flow of a liquid Ethylene Glycol & EtOH

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Surface Tension the force that causes the surface of a liquid to contract

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Paper Clip

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Adhesive Forces the forces of attraction between a liquid and a surface

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Capillary Action Meniscus

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SOLIDS

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Amorphous Solids Arrangement of particles lacks an ordered internal structure. As temp is lowered, molecules move slower and stop in somewhat random positions.

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Crystalline Solids Atoms or ions are held in simple, regular geometric patterns Ionic Molecular Atomic

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Atomic Solids Noble Gases Network Metallic

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X-ray Crystallography How do you determine the spacing and position of atoms in an organized solid like a crystal?

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X-ray Crystallography Bragg discovered that nuclei of atoms or ions in a crystal will defract x-rays and form a pattern on photofilm that can be analyzed using simple trig & geometry

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X-ray Crystallography Use the fact that x-rays are part of the electromagnetic spectrum Nuclei in crystalline solids are in layers that can act as a diffraction grating to the x-ray wavelength

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Crystalline Solids Diffract X-rays

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Let = extra distance that i must travel so that r is in- phase with r = xy + yz or = 2xy

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Using trigonometry:

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But for constructive interference

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= n n = 2d sin BRAGG EQUATION

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1. X-rays from a copper x-ray tube ( = 154 pm) were diffracted at an angle of by a crystal of Si. What is the interplanar spacing in silicon?

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Solids

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Types of Solids 1. Atomic (Metals) 2. Molecular (Ice) 3. Ionic (NaCl)

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Structures of Metals

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The unit cell is the smallest representation of the building block of the regular lattice

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Unit Cell Only 23 different unit cells have been defined Called Brave Lattices Patterns are determined by crystallography

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Coordination Number CN is related to net atoms found within the unit cell CN is the number of atoms closest to any given atom in a crystal

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There are three Cubic Unit Cell Types (pc) primitive cubic or simple cubic (8 corners of cube) x (1/8 each corner in cell) = 1 net atom in cell CN = 6 (bcc) body centered cubic (1 atom in cube) + [(8 corners of cube) x (1/8 each corner in cell)] = 2 net atoms in cell [(8 corners of cube) x (1/8 each corner in cell)] = 2 net atoms in cell CN = 8 (fcc) face centered cubic (fcc) face centered cubic [(6 faces of cube) x (1/2 of atom in cell)] + [(8 corners of cube) x (1/8 each corner in cell)] = 4 net atoms in cell [(8 corners of cube) x (1/8 each corner in cell)] = 4 net atoms in cell orCN = 12 (1 atom in cube) + (1 atom in cube) + [(12 edges of cube) x (1/4 each edge in cell)] = 4 net atoms in cell [(12 edges of cube) x (1/4 each edge in cell)] = 4 net atoms in cell CN = 12

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1 Atom per Cell CN = 6 l = 2r l

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2 Atoms per Cell CN = 8 l

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4 Atoms per Cell CN = 12 l

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Summary Unit Cell Atoms Per Cell C.N. Length Of Side Cubic16 2r BCC28 FCC412

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Face-centered cubic Primitive cubic

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Structures of Metals Closest Packing

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Structures of Metals Closest Packing 1. Hexagonal 2. Cubic

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A-B A-B-C

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(Primitive cubic)

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2. Al crystallizes as a face centered cube. The atomic radius of Al is 143 pm. What is the density of Al in g/cm 3 ?

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3. What is the percent of empty space in a body centered unit cell?

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VAPOR PRESSURE Evaporation and equilibrium

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Vapor Pressure pressure in space above a liquid in a CLOSED container

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PROPERTIES 1. closed container 2. temperature dependent 3. subject to all laws of partial pressures 4. dynamic system

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Vapor Pressure temperature dependent P T

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To plot in a linear fashion, must transform the variables.

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ln P 1/T (K)

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y = mx + b & R = J/K mol

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therefore:

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ln P 1/T (K) define 2 points 1 2

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Subtract: ln P 1 - ln P 2

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Collect terms & factor: Clausius- Clapeyron Equation

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SUMMARY OF IDEAS TO BE CONSIDERED: 1. vapor pressure - temperature dependent 2. volume determines time needed to establish vapor pressure - NOT final pressure

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3. H (condensation) = - H (vaporization) 4. Critical Point - (T,P) above which vapor cannot be liquefied - regardless of pressure 5. Boiling: temperature where vapor pressure of liquid is the same as atmospheric pressure

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4. The temperature inside a pressure cooker is C. What is the vapor pressure of water inside the pressure cooker?

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PHASE DIAGRAMS

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PHASE DIAGRAM A representation of the phases of a substance in a closed system as a function of temperature and pressure

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Normal Boiling Point Temperature at which the vapor pressure of the liquid is exactly 1 atmosphere

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Normal Melting Point Temperature at which the solid and liquid states have the same vapor pressure when the total P = 1 atm

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Triple Point The point on a phase diagram at which all three states of a substance are present

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Critical Temperature Temperature above which vapor cannot be liquified no matter what pressure is applied

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Critical Pressure Minimum pressure required to produce liquefaction of a substance at the critical temperature

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Critical Point Ordered pair of Critical Temperature & Critical Pressure

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CO 2

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H2OH2O

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sulfur

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