Properties of Substances and Mixtures

Intermolecular Forces (IMFs)

London Dispersion Forces (LDF):
- Present in all substances; sole force in nonpolar substances.
- Temporary dipoles due to random electron motion induce dipoles in neighboring molecules, leading to Coulombic attraction.
- Increase with greater contact area, more electrons/larger electron cloud, and pi bonding (polarizability).
Dipole-Induced Dipole:
- Occurs between polar and nonpolar molecules.
- Increases with polarity of the polar molecule and polarizability of the nonpolar molecule.
Dipole-Dipole:
- Occurs between two polar molecules.
- Strength increases with greater polarity and favorable orientations.
- Typically stronger than LDF, but data should be checked.
Hydrogen Bonding:
- Strong form of dipole-dipole interaction.
- Requires a partially positive hydrogen atom attached to N, O, or F on one molecule, attracted to a partially negative N, O, or F on another molecule.
Ion-Dipole:
- Occurs between an ion and a polar molecule.
- Usually stronger than dipole-dipole interactions.

Properties depend on the strength and type of IMFs (boiling point (BP), vapor pressure (VP), melting point (MP)).
- When boiling, all IMFs must be overcome to vaporize a substance.
Ionic Solids:
- Strong interactions between ions result in low VP and high MP/BP.
- Brittle due to repulsions between like charges.
- Conduct electricity when ions are mobile (solutions or molten state).
Covalent Network Solids:
- 3D (or 2D for graphite) covalent bonds throughout the structure.
- Very strong, leading to very high MP/BP.
- Hard/rigid due to fixed bond angles.
- Examples: diamond, Buckyball (C60), graphite, SiC, SiO2.
Molecular Solids:
- Individual molecules held together by relatively weak IMFs.
- High VP and low MP/BP.
- Do not conduct electricity.
Metallic Solids:
- Metal atoms in a sea of valence electrons.
- Can form alloys (interstitial and substitutional).
- Conduct heat and electricity.
Biomolecules/Polymers:
- Large molecules with intramolecular forces affecting shape/properties.

Solids:
- Particles in regular, crystalline arrangements or amorphous structures.
- Limited particle motion; no translational kinetic energy.
- Structure determined by interparticle attractions.
Liquids:
- Particles close together but able to move and collide.
- Arrangement and movement depend on polarity, hydrogen bonding, and temperature.
- Molar volume similar to corresponding solid.
Gases:
- Constant random motion in straight lines until collision.
- Frequency of collisions depends on volume, pressure, and temperature.
- Limited IMFs; no definite shape or volume.

Relates pressure (P), volume (V), moles (n), and absolute temperature (T) of a gas: PV = nRT
- R is the Universal Gas Constant (0.08206 Latm/molK).
Combined Gas Law derivation: \frac{PV}{nT} = R = \frac{PV}{nT}
Dalton's Law of Partial Pressures: Total pressure is the sum of individual pressures (P = P1 + P2 + P_3…).
- Application: Gases collected by bubbling through water require accounting for water vapor pressure.
Mole Fraction (X):
- Represents the fraction of the sample (in moles) for one of the gases.
- Mole fraction * total pressure = pressure of the gas in question.

Real gases deviate from ideal behavior at high pressure or low temperature.
Factors causing deviation:
- Volume of particles: Significant for larger particles, increases the P*V term.
- Intermolecular Forces: Increase with stronger IMFs, decreases the P*V term.
- Maxwell-Boltzmann distribution: Describes particle energies at different temperatures.

Solutions: Homogeneous mixtures where a solute is dissolved in a solvent.
Heterogeneous mixtures: Non-uniform composition.
Molarity:
- Common unit for solution concentration: Molarity = \frac{moles \, of \, solute}{Liter \, of \, solution}
- Ion concentration depends on the ratio of atoms in the formula.

Chromatography:
- Separates components based on differences in IMFs.
- Types: Paper, Column, and Thin-Layer Chromatography (TLC).
- Mobile phase (solvent) and stationary phase.
- Column chromatography: Use for material recovery.
- R_f \, value = \frac{distance \, traveled \, by \, dye}{distance \, traveled \, by \, solvent}
Distillation:
- Separates mixtures based on differences in boiling points.
- Repeated boiling and condensation of vapors.

Miscible: Solute and solvent will mix.
Immiscible: Solute and solvent do not mix.
Substances with similar IMFs tend to be miscible.
Solution formation steps:
- Solute separation (requires energy).
- Solvent separation (requires energy).
- Solvent-solute attraction (releases energy).

Spectroscopy: Study of matter's interaction with electromagnetic radiation.
Microwave Rotational Spectroscopy:
- Microwaves cause molecules to rotate due to interaction with molecular dipole.
Infrared (IR) Vibrational Spectroscopy:
- Measures atomic vibrations, determines functional groups.
Ultraviolet-Visible (UV-Vis) Light Spectroscopy:
- Photons excite electrons to higher energy levels.
- Energy released as EM radiation during transitions in electronic energy levels.

Photoelectric Effect:
- Light shone on a material's surface ejects electrons if energy exceeds binding energy (or shorter wavelength/higher frequency than threshold).
- Photon absorption/emission changes atom/molecule energy.
Photon energy:
- E = hv
- h (Planck's constant) = 6.626 \times 10^{-34} m/second
- v (frequency) in Hertz (1/sec).
- Electron energy: E = \frac{1}{2} mv^2
Combined equations:
- E = \frac{hc}{\lambda}
- c (speed of light) = 3.00 \times 10^8 m/sec
- λ = wavelength (m).