Transcript PPT
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 (SO 2 , CHCl 3 , 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 3. Dipole – Dipole 4. Dipole-Induced Dipole
1. Ion - Ion 2. Ion - Dipole 3. Dipole – Dipole 4. Dipole-Induced Dipole 5. Dispersion Forces
Dispersion Forces Process of distorting an electron cloud by electrostatic forces of attraction and repulsion.
Weakest of the intermolecular forces.
Non-polar molecules Momentary attractions & repulsions Temporary dipoles established
Dispersion forces also called van der Waal’s forces
LIQUIDS & SOLIDS
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,
Hº vap Energy required to convert one mole of liquid to one mole of the corresponding gas at the BP.
Always endothermic,
H vap is positive.
Liquids having greater attractive forces have higher
H vap
Condensation KE
1 2 mv 2 Opposite of Evaporation Condensation -- Exothermic
Viscosity
a measure of the resistance to flow of a liquid
Ethylene Glycol & EtOH
Surface Tension
the force that causes the surface of a liquid to contract
Paper Clip
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.
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: sin
xy d
xy
d sin
D
2 d sin
But for constructive interference
But for constructive interference n
l D
= n
l
= 2d sin
BRAGG EQUATION
1. X-rays from a copper x-ray tube (
l
= 154 pm) were diffracted at an angle of 14.22
0 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
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 (1 atom in cube) + [(12 edges of cube) x (1/4 each edge in cell)] = 4 net atoms in cell CN = 12
l 1 Atom per Cell CN = 6 l = 2r
l 2 Atoms per Cell CN = 8
2
2
2
2
4 r 3
l 4 Atoms per Cell CN = 12
2
2
2
2 r 2
Unit Cell Cubic BCC FCC Summary Atoms Per Cell C.N.
1 6 Length Of Side 2r 2 8 4r 3 4 12 2r 2
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. The atomic radius of Al is 143 pm. What is the density of Al in g/cm 3 ?
3. What is the percent of empty space in a body centered unit cell?
VAPOR PRESSURE
Evaporation and equilibrium
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
P Vapor Pressure temperature dependent T
To plot in a linear fashion, must transform the variables.
ln P 1/T (K)
y = mx + b where : m
D
H vap R & R = 8.314 J/K mol
therefore: ln P
D
H vap R
1 T
b
ln P 1 define 2 points 2 1/T (K)
ln P 1
D
H R vap
1 T 1
b ln P 2
D
H vap R
1 T 2
b
Subtract: ln P 1 - ln P 2
D
H R vap
1 T 1
b
-
D
H R vap
1 T 2
b
Collect terms & factor: ln
P P 2 1
D
H vap R
1 T 2
1 T 1
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.
D
H (condensation) = -
D
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 115 0 C. 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
CO 2
H 2 O
sulfur