Presentation on theme: "AP Notes Chapter 12 & 13 Intermolecular Forces, Liquids and Solids."— Presentation transcript:
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 Waals 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. 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.
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
Opposite of Evaporation Condensation -- Exothermic Condensation
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
Adhesive Forces the forces of attraction between a liquid and a surface
Capillary Action Meniscus
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 = extra distance that i must travel so that r is in- phase with r = xy + yz or = 2xy
But for constructive interference
= n n = 2d sin BRAGG EQUATION
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?
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 [(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
1 Atom per Cell CN = 6 l = 2r l
2 Atoms per Cell CN = 8 l
4 Atoms per Cell CN = 12 l
Summary Unit Cell Atoms Per Cell C.N. Length Of Side Cubic16 2r BCC28 FCC412
Face-centered cubic Primitive cubic
Structures of Metals Closest Packing
Structures of Metals Closest Packing 1. Hexagonal 2. 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
Vapor Pressure temperature dependent P T
To plot in a linear fashion, must transform the variables.
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 C. What is the vapor pressure of water inside the pressure cooker?
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