General Chemistry 2: Intermolecular Forces & Properties

• Course Outcome 1 for General Chemistry 2 covers the properties of liquids and solids and interpreting phase diagrams.
• Essential Question: What influences the properties of matter?

Intermolecular Forces

• Intermolecular forces are attractive forces between molecules and are related to properties such as boiling point and surface tension in solids and liquids, and ideal/real gas behavior in gases.
• Relative strength of intermolecular forces from weakest to strongest:
  • Dispersion (0.05-40 kJ/mol)
  • Dipole-Dipole (5-25 kJ/mol)
  • Hydrogen Bonding (10-40 kJ/mol)
  • Ion Dipole (40-600 kJ/mol)
• Essential Question: How do the intermolecular forces influence the properties of matter?

Properties of Liquids

• Surface Tension
  • Surface tension measures the energy to stretch/increase the surface area of a liquid.
  • It is the property of a liquid to resist an external force, assuming a lesser surface area.
  • Liquids with strong intermolecular forces have high surface tension.
• Capillary Action
  • Capillary action is a liquid's tendency to rise in narrow tubes or be drawn into small openings.
• Cohesive Force
  • Cohesive force is the interaction between like molecules such as water molecules.
• Adhesive Force
  • Adhesive force is the interaction between different substances such as water and glass.
    • Meniscus shape:
      • Concave occurs when adhesive forces are greater than cohesive forces, resulting in greater capillary action.
      • Convex occurs when cohesive forces are greater than adhesive forces, resulting in less capillary action.
• Viscosity
  • Viscosity measures a fluid's resistance to flow.
  • Liquids with strong intermolecular forces exhibit higher viscosity.
• Vapor Pressure
  • Vapor Pressure is the pressure exerted by the vapor resulting from the evaporation of a liquid above the liquid in a closed container.
  • Liquids with stronger IMFs have lower vapor pressures.
• Boiling Point
  • Boiling Point of a liquid is the temperature at which its vapor pressure equals the external/atmospheric pressure (1 atm).
  • Liquids with stronger IMFs have higher boiling points.
• Heat of Vaporization/Condensation
  • Heat of vaporization (∆Ηvap) is the energy required to vaporize 1 mole of a liquid at its boiling point.
  • Heat of condensation (∆Hcond) is the energy released when 1 mol condenses.
  • The stronger the intermolecular forces of attraction, the higher the heat of vaporization and condensation.

Liquid Properties

• Surface Tension - Strong Intermolecular Force: greater surface tension.
• Capillarity - Strong Intermolecular Force: greater cohesive force than adhesive force.
• Viscosity - Strong Intermolecular Force: greater viscosity.
• Vapor Pressure - Strong Intermolecular Force: low vapor pressure.
• Boiling Point - Strong Intermolecular Force: high boiling point.
• Heat of Vaporization and Condensation - Strong Intermolecular Force: high heat of vaporization and condensation.

Properties of Solids

• Crystalline Solid: Possesses a long-range order where atoms, molecules, or ions occupy specific, predictable places.
• Amorphous Solid: Lacks a defined arrangement or long-range molecular order
• Unit Cell: basic repeating structural unit of a crystalline solid

Cell Symmetries

• Simple Cubic Lattice
  • primitive cubic
  • 1 net atom per unit cell
• Body-Centered Cubic Lattice
  • Coordination number is 8
  • It has an additional atom, of the same type as those at the corners, at the center of the cube
  • 2 net atoms per unit cell
• Face-Centered Cubic Lattice
  • Coordination Number is 6
  • Spheres exist at the center of each of the six faces of the cube, in addition to the eight corner spheres
  • 4 net atoms per unit cell
• Types of Crystalline Solids
  • Types of Crystalline Solids:
    • Ionic Crystal
    • Molecular Crystal
    • Covalent Network Crystal
    • Metallic Crystal

Types of Crystalline Solids

• Ionic Crystals:
  • Lattice points are occupied by cations and anions, held together by electrostatic attraction.
  • They are hard and brittle, have a high melting point, and are poor conductors of heat and electricity.
• Molecular Crystals:
  • Lattice points are occupied by molecules held together by intermolecular forces.
  • They are soft with low melting points and poor conductors of heat and electricity.
• Covalent Network Crystals:
  • Lattice points are occupied by atoms, held together by covalent bonds.
  • They are hard, have high melting points, and are poor conductors of heat and electricity.
• Metallic Crystals:
  • Lattice points are occupied by metal atoms held together by metallic bonds
  • Characteristics range from soft to hard with low to high melting points and good conduction of heat/electricity

Molecular Forces and Properties of Solids

• Ionic Crystal
  • Held together by electrostatic force: hard, brittle, high melting point, and poor conductors of heat and electricity.
• Molecular Crystal
  • Held together by intermolecular force: soft, low melting point, and poor conductors of heat and electricity.
• Covalent Network Crystal
  • Held together by covalent bond: hard, high melting point, and poor conductors of heat and electricity.
• Metallic Crystal
  • Held together by a metallic bond: range from soft to hard with low to high melting points and good conductors of heat/electricity.

Phase Changes

• Phase changes transform matter from one state to another through absorption or evolution of heat.
• Transitions include:
  • Sublimation: Solid to gas
  • Vaporization: Liquid to gas
  • Melting: Solid to Liquid
  • Freezing: Liquid to Solid
  • Condensation: Gas to Liquid
  • Deposition: Gas to Solid

Liquid-Vapor Equilibrium

• Vaporization is the process by which liquid changes to the gaseous state at a liquid's boiling point.
• Evaporation is the process by which liquid changes to the gaseous state below its boiling point.
• Condensation occurs when gas molecules condense to become liquid.
  • It occurs when molecules strike a liquid's surface and are trapped by intermolecular forces.

Solid-Liquid Equilibrium

• Freezing is the transformation of a liquid to solid.
• Melting is the transformation of a solid to liquid.
  • The freezing point of a liquid or the melting point of a solid defines the temperature at which solid and liquid phases coexist in equilibrium.

Solid-Vapor Equilibrium

• Sublimation is the process in which molecules directly transition from the solid phase to the vapor phase.
• Deposition is the transition from vapor to solid directly.
  • Molar heat of sublimation (∆Ηyap) signifies the energy required to sublime 1 mole of a solid.

Phase Diagram

• Diagram best represents the overall relationships among a substance's solid, liquid, and vapor phases, summarizing the temperature and pressure conditions at which a substance exists in each phase

Features of a Phase Diagram

• Includes 3 areas, 3 lines, and 2 points.
  • The three areas mark solid, liquid, and vapor phases under certain conditions, indicating the stable state of a system in equilibrium.
  • The three lines are:
    • Green line divides the solid and liquid phases and represents melting and freezing points. It shows the solids and liquids effect of pressure on equilibrium.
    • Blue line divides the liquid and gas phases, representing vaporization and condensation points; shows the liquid and gas effect of pressure on equilibrium.
    • Red line divides solid and gas phases, representing sublimation and deposition points.
  • There are two key points:
    • Triple Point: the point on the phase diagram where all three states of matter (solid, liquid, gas) coexist.
    • Critical Point: terminates the liquid/gas phase line. It is the set of temperature and pressure where liquid and gaseous phases merge into a single phase known as a supercritical fluid. Critical temperature represents the maximum one at which a liquid is able to be liquefied, and critical pressure signifies the maximum pressure at which a liquid can be liquefied.

This note covers intermolecular forces and their influence on the properties of matter. It covers the relative strength of intermolecular forces such as Dispersion, Dipole-Dipole, Hydrogen Bonding, and Ion Dipole. It also looks at the properties of liquids, surface tension, viscosity, and vapor pressure.