CHEM 105N - Chapter 8 Notes: Solids, Liquids, and Gases

Intermolecular Forces

Attractions between molecules weaker than intramolecular bonds.
Affect physical properties: boiling/melting points, viscosity, surface tension, capillary action.

States of Matter

Gases: Particles with little attraction, move randomly.
Liquids: Particles held close, move around each other.
Solids: Particles in ordered arrangement, vibrate in place.

Properties of States of Matter

Gas: Assumes volume/shape, expands, compressible, flows readily, rapid diffusion.
Liquid: Assumes shape, doesn't expand, incompressible, flows readily, slow diffusion.
Solid: Retains shape/volume, doesn't expand, incompressible, doesn't flow, extremely slow diffusion.

Phase Changes

Phase transitions involve energy changes.
Melting, vaporization, sublimation: require energy (breaking intermolecular forces).
Freezing, condensation, deposition: release energy (forming intermolecular forces).

Polar Covalent Bonds and Dipole Moments

Electronegativity differences create bond dipoles.
Molecular polarity depends on bond polarity and molecular geometry.
Polar molecule: dipole moments do not cancel.
Nonpolar molecule: dipole moments cancel.

Types of Intermolecular Forces

Weaker than ionic/covalent bonds.
Types: Ion-dipole, Van der Waals (Dipole-dipole, London dispersion), Hydrogen bonds.

Ion-Dipole Forces

Attraction between ion and polar molecule.
Example: NaCl in water.

Dipole-Dipole Forces

Occur between neutral polar molecules.
Positive dipole attracted to negative dipole.
Higher polarity leads to higher boiling point (for similar mass/size).

London Dispersion Forces (LDF)

Exist in all molecules (polar or nonpolar).
Instantaneous dipole induces a dipole in neighboring atom.
Factors affecting LDF: size (molecular weight) and molecular shape (linear vs. symmetric).

Hydrogen Bonds

Strong dipole-dipole interaction between H bonded to O, N, or F and another electronegative atom (O, N, F).
Intermolecular: between molecules, responsible for high boiling point of water.
Intramolecular: within a single molecule.

IMFs Relative Strengths

Ionic/Covalent bonds > Hydrogen bond > Dipole-dipole > London Dispersion.

Types of Intermolecular Forces Summary

Ions and polar molecules: Ion-dipole forces.
Hydrogen atoms bonded to N, O, or F: Hydrogen bonding.
Polar molecules (no ions, no H to N/O/F): Dipole-dipole forces.
Nonpolar molecules: London dispersion forces only.

Characteristics of Gases

Composed mainly of nonmetallic elements with simple formulas and low molar masses.
Expand to fill containers, highly compressible, low densities, form homogeneous mixtures.

Properties That Define the State of a Gas Sample

Temperature, pressure, volume, amount of gas (moles).

Pressure

$P = \frac{F}{A}$
Atmospheric pressure: weight of air per area.

Units of Pressure

Pascals (Pa): $1 Pa = 1 N/m^2$
Bar: $1 bar = 10^5 Pa$
mm Hg or torr.
Atmosphere: $1 atm = 760 torr = 760 mmHg = 101.325 kPa$

Standard Pressure

1 atm, 760 mmHg, 760 torr, 101.325 kPa.

Boyle’s Law

Volume inversely proportional to pressure at constant temperature.
$P<em>1V</em>1 = P<em>2V</em>2$

Charles’s Law

Volume directly proportional to absolute temperature at constant pressure.
$\frac{V<em>1}{T</em>1} = \frac{V<em>2}{T</em>2}$

Gay-Lussac’s Law of Combining Volumes

Volume of reacting gases in small whole numbers at constant temperature/pressure.
Example: $2H<em>2 + O</em>2 → 2H_2O$

Avogadro’s Law

Volume directly proportional to number of moles at constant temperature/pressure.
$\frac{V<em>1}{n</em>1} = \frac{V<em>2}{n</em>2}$
At STP, one mole of ANY gas occupies 22.4 L.

Ideal-Gas Equation

$PV = nRT$
R (Ideal gas constant) = 0.08206 L⋅atm/mol⋅K or 8.314 J/mol⋅K

Dalton’s Law of Partial Pressures

Total pressure is the sum of partial pressures.
$P<em>t = P</em>1 + P<em>2 + P</em>3 + …$

Standard Temperature and Pressure (STP)

Standard temperature: 0 °C or 273 K.
Standard pressure: 1 atm (760 mmHg).

Molar Volume, STP

At STP: 1 mole of gas occupies 22.4 L.