Intermolecular Forces

Dipole-Dipole Attraction & Repulsion

Molecules maximize + - interactions and minimizes + + and - - interactions. Diople-Dipole forces are typically 1% as strong as covalent bonding. Hydrogen Bonding: F ,O ,N e.g. B.P. \(H_2O > H_2S\) and \(HF > HCl\)

London Dispersion Force

Instantaneous dipole induce a similar dipole in a neighboring atom. Large atoms with many electrons exhibit higher polarizability. e.g. F.P. \(He < Ne < Ar < Kr < Xe\)

Liquid

Surface Tension - uneven pull on the surface molecules draw them into the liquid body, causing a sphere. Capillary Action - cohesive force (liquid-liquid) + adhesive force (liquid-container), causing concave/convex meniscus. Viscosity - e.g. glycerol with O-H groups and large molecules.

Solid

Categories: crystalline solid (lattice and unit cell) vs amorphous solid. Simple Cubic, Body-centered Cubic (alkali metals), Face-centered Cubic. X ray diffraction, Bragg equation \(2d\sin \theta = n\lambda\)

Types

Atomic Solids - Metallic(Delocalized Convalent), Network(Directional Convalent), 8A(London Dispersion) Molecular Solids - Dipole-Dipole / London Dispersion Ionic Solids - Ionic

Bonding in Metals - Closest Packing

Hexagonal Closets Packing (hcp) abab: magnesium and zinc Cubic Closest Packing (ccp, faced-centered unit cell) abcabc: aluminum, iron, copper, cobalt, and nickel Closest Pack Structures

electron sea model - malleability, ductility

band model, molecular orbital (MO) model - electrons travel around valence atomic orbitals. When many metal atoms interact, large number of molecular orbitals become closely spaced and form bands. Core electrons are localized, but valence electrons occupy closely spaced molecular obitals, which are partially filled.

Metal Alloys

Substitutional Alloy: brass, sterling silver, plumber’s solder Interstitial Alloy Mild(<0.2%)-Medium(0.2-0.6%)-High(0.6-1.6%) Steels

Network Solids

Conductivity of Graphite: closely spaced \(\Pi\) orbitals. Silica (Quartz(\(SiO_2\)), \(SiO_4\) tetrahedra) and Silicate (\(SO_{4}^{4-}\) tetrahedra) Glass + \(Na_2CO_3\) / \(K_2O\)

Semiconductors

Molecular Solids

Ionic Solids

Trigonal Holes

Tetrahedral Holes (r/R = 0.225-0.414) - 8 in CCP

Octahyral Holes (r/R = 0.414-0.732) - 4 in CCP

Vapor Pressure

$$\ln P_{vap} = -\frac{\Delta H}{R} (\frac{1}{T}) + C$$

Phase Diagram

The melting and boiling points for a substance are determined by the vapor pressures of the solid and liquid state. e.g. the vapor pressure of ice increases more rapidly than the vapor pressure of water -- below 0 degrees water has a higher vapor pressure, therfore frozen water into ice; above 0 degrees ice has a higher vapor pressure, thus melting into water. Melting point - liquid and solid have identical vapor pressures.

Supercooled - haven't achieve the degree of organization for ice.

Superheated - bumping, avoid by adding boiling chip (porous ceramic).

Water, Carbon Dioxide, Diamond-Graphite, Sulfur

Solution

Mass Percent, Mole Fraction, Molarity, Molality

Enthalpy of Solution

Separating Solute + Expanding Solvent + Form Solution Polar vs Nonpolar solute/solvent Fat-soluble(hydrophobic) vs Water-solubale(hydrophilic)

Pressure Effects - Henry's Law

$$C_M = kP$$

most accurate for dilute solutions of gasses that do not dissociate/react with the solvent

Temperature Effects

Thermal Pollution - solubility of a gas in water typically decreases with increasing temperature.

Raoult's Law

For nonvolatile solute,

$$P_{solution} = X_{solvent}P^0_{solvent}$$

Non-ideal Solutions

For solution of two volatile liquids, compared to

$$P_{solution} = X_{A}P^0_{A} + X_{B}P^0_{B}$$

positive(AA & BB > AB, endothermic)/negative deviation(AA & BB < AB, exothermic) of Raoult's law

Colligative Properties

Van't Hoff Factor

$$i = \frac{moles\ of\ particles}{moles\ of\ dissolved\ solute}$$

Boiling-Point Elevation

According to the Raoult's Law, it requires higher temperature to get to 1 atm (boiling vapor pressure) than pure solvent because the nonvolatile solute lowers the vapor pressure.

$$\Delta T = i C_m K_b$$

and liquid/vapor line is shifted to higer temperature.

Freezing-Point Depression

According the the melting point definition (liquid and solid vapor pressure at equilibrium), the vapor pressure of a liquid solution will be lower then that of the pure solvent, causing the freezing-point to drop.

$$\Delta T = i C_m K_f$$

Osmotic Pressure

with a semipermeable membrane (allows solvent but not solute to pass). Dialysis(透析)

$$\Pi = i C_M RT$$

Hypertonic-Isotonic-Hypotonic

Fractional Distillation

Assuming two liquid solvents, B.P. A < B. At temperature T with mole fraction (of B) m the liquid is at equilibrium with mole fraction n (m>n) gas.

Distill at T1>T2>T3>... using Theoratical Plate, the mole fraction of A in vapor increases.

Colloids

Tyndall Effect - scattering of light by particles

Colloid(Colloidal Dispersion) - suspension of particles Aerosol, Foam, Emulsion, Sol, Gel

Coagulation - destroy colloids, by heating, adding a electrolyte or electrostatic precipitator.

References

S. Zumdal, S. Zumdahl and H. Hsu. 2015. General Chemistry. Cengage Learning Asia

蔡蘊明 基礎普通化學 NTU OCW