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

1. Ion - Ion

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

1. Ion - Ion 2. Ion - Permanent Dipole

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)

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

Occurs between molecules with permanent dipoles (SO2 , CHCl3 , etc)

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

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

Dimer of Acetic Acid

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

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

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

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

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

Momentary attractions & repulsions Temporarydipoles established Non-polar molecules Momentary attractions & repulsions Temporarydipoles established

Dispersion forces also called van der Waal’s forces

LIQUIDS & SOLIDS

various intermolecular forces holding a liquid together Cohesive Forces various intermolecular forces holding a liquid together

Vaporization 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.

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

Condensation Opposite of Evaporation Condensation -- Exothermic

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

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

Paper Clip

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

Capillary Action Meniscus

SOLIDS

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

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

Atomic Solids Noble Gases Network Metallic

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

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

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

Crystalline Solids Diffract X-rays

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

Using trigonometry:

But for constructive interference

But for constructive interference D = nl nl = 2d sin q BRAGG EQUATION

1. X-rays from a copper x-ray tube ( = 154 pm) were diffracted at an angle of 14.220 by a crystal of Si. What is the interplanar spacing in silicon?

Solids

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

Structures of Metals

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

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

CN is the number of atoms closest to any given atom in a crystal 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

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 CN = 8 (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 or CN = 12 [(12 edges of cube) x (1/4 each edge in cell)] = 4 net atoms in cell CN = 12

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

2 Atoms per Cell CN = 8 l

4 Atoms per Cell CN = 12 l

Summary 2r Unit Cell Atoms Per Cell C.N. Length Of Side Cubic 1 6 BCC 8 FCC 4 12

Primitive cubic Face-centered cubic

Structures of Metals Closest Packing

Structures of Metals Closest Packing 1. Hexagonal 2. Cubic

A-B A-B-C

(Primitive cubic)

2. Al crystallizes as a face centered cube 2. Al crystallizes as a face centered cube. The atomic radius of Al is 143 pm. What is the density of Al in g/cm3?

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

VAPOR PRESSURE Evaporation and equilibrium

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

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

temperature dependent Vapor Pressure temperature dependent P T

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

ln P 1/T (K)

y = mx + b & R = 8.314 J/K mol

therefore:

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

Subtract: ln P1 - ln P2

Clausius-Clapeyron Equation Collect terms & factor: Clausius-Clapeyron Equation

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

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

4. The temperature inside a pressure cooker is 1150C 4. The temperature inside a pressure cooker is 1150C. What is the vapor pressure of water inside the pressure cooker?

PHASE DIAGRAMS

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

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

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

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

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

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

Critical Point Ordered pair of Critical Temperature & Critical Pressure

CO2

H2O

sulfur