3.1-3.3

3.1 Intermolecular Forces

  • Basics of Intermolecular Forces

    • Water boiling involves molecules separating from each other, while atoms remain bonded (H2O(l) to H2O(g)).

    • Intramolecular Forces: Interactions within a single molecule (e.g., covalent bonds).

    • Intermolecular Forces: Interactions between two molecules (e.g., Coulombic forces, abbreviated as IMF).

Dipole-Dipole Interactions

  • Occur between two polar molecules due to partial positive and negative charges.

    • Molecules orient to maximize attraction (positive to negative charges).

    • Dipole moment: Increased dipole moment correlates with increased attraction and polarity.

London Dispersion Forces (LDFs)

  • Attraction between nonpolar molecules; all molecules experience LDF.

    • Caused by fluctuations in electron distribution, creating temporary dipoles.

    • Factors affecting LDF strength:

      • Ease of electron dispersion

      • Size of electron cloud: larger clouds = stronger LDF

      • Surface area: increased surface area leads to stronger LDF.

      • More branches in a molecule reduce strength due to decreased surface area.

Hydrogen Bonding

  • A special case of dipole-dipole interaction, explains strong IMFs in water.

    • Occurs specifically in molecules with hydrogen bonded to F, O, or N (e.g., H2O).

    • The highly electronegative oxygen atom attracts hydrogen electrons, creating partial charges that lead to hydrogen bonding between molecules.

Properties Explained by IMFs

  • Properties Affected by Increased IMF Strength:

    • Melting/boiling point

    • Surface tension

    • Viscosity

    • Heat of vaporization

  • Properties Decreased by Increased IMF Strength:

    • Vapor pressure

    • Volatility (ease of evaporation)

Comparing Magnitude of IMFs

  • Size differences among molecules do not assume IMF strength unless specified.

  • For similarly sized molecules:

    • Hydrogen bonding > Dipole-dipole > LDF

3.2 Properties of Solids

  • Determined by type and strength of IMFs present.

Types of Solids

  • Lattice: A 3D arrangement of points defining solid structure.

    • Lattice points: Positions of constituent particles.

Ionic Solids

  • Formed from fully positive and negative ions.

    • Characteristics:

      • High melting/boiling points

      • Low vapor pressure

      • Brittle due to electron repulsion leading to crumbling

      • Smaller ions = higher attraction; higher charge = greater attraction.

Network Covalent Solids

  • Composed of atoms at lattice points with strong covalent bonds (nonmetals, e.g., graphite, diamond).

  • Characteristics:

    • Hard and strong

    • High melting points

    • Rigid and brittle due to fixed bond angles.

Molecular Solids

  • Formed by weaker IMFs.

  • Characteristics:

    • Low melting points

    • Non-conductive due to tightly packed electrons (e.g., H2O, CO2).

Metallic Solids

  • Variable hardness, malleable.

  • Characteristics:

    • Melting/boiling point depends on electron count.

    • Good electrical and thermal conductivity.

    • Generally insoluble except in metal mixtures (alloys).

3.3 Solids, Liquids, and Gases

  • Solids:

    • Can be crystalline (3D structured) or amorphous (no orderly arrangement).

    • Structure influenced by interparticle interactions and packing ability.

  • Liquids:

    • Particles are closely packed but constantly moving and colliding.

    • Movement influenced by IMFs and nature of particles.

  • Gases:

    • Particles are in constant motion with no defined shape or volume due to minimal particle interaction.

    • Behavior influenced by temperature, pressure, and volume.