genchem 2

• Non-Polar Covalent Bond


  Bonding electrons shared equally between two atoms. No charges on atoms.
• Polar Covalent Bond


  Bonding electrons shared unequally between two atoms. Partial charges on atoms.
• Ionic Bond


  Complete transfer of one or more valence electrons. Full charges on resulting ions.
• Electronegativity


  A measure of the tendency of an atom to attract a bonding pair of electrons.
• Van Der Waals Forces


  Intermolecular forces of attraction between neutral molecules.
• The Nobel Prize in Physics 1910 winner (Johannes van der Waals) for his work on the equation of state for gases and liquids.
• Intramolecular forces


  Forces within a molecule or ionic compound.
• Intermolecular forces

  Forces between molecules or ions and molecules.
• 3 Types of van der Waals Forces

  • Dipole-Dipole forces
  • London Dispersion forces
  • Hydrogen bonding
• Dipole-Dipole Forces


  Forces of attraction that occur between polar molecules. Effective only when polar molecules are very close. Relatively weak, tend to be liquids or gases at room temperature.
• Hydrogen Bonding


  A special type of dipole-dipole interaction between the hydrogen atom in a polar bond and an unshared electron pair of an element that is very electronegative (F, O, or N). Unusually strong (4x stronger than dipole-dipole).
• London Dispersion Forces


  Forces that arise as a result of temporary dipoles induced in the atoms or a molecules. Occur between neutral non-polar molecules. Weak.
• Condensed phases


  Solids and liquids
• Properties of Gas


  • Assumes both volume and shape of its container
  • Expands to fill its container
  • Is compressible
  • Flows readily
  • Diffusion within a gas occurs rapidly
• Properties of Liquid


  • Assumes the shape of a portion of the container it occupies
  • Does not expand to fill its container
  • Is virtually incompressible
  • Flows readily
  • Diffusion within a liquid occurs slowly
• Properties of Solid


  • Retains its own shape and volume
  • Does not expand to fill is container
  • Is virtually incompressible
  • Does not flow
  • Diffusion within a solid occurs extremely slowly
• Gas


  Kinetic energies > Energies of attraction
• Liquid


  Comparable kinetic energies and energies of attraction
• Solid


  Energies of attraction > Kinetic energies
• Dispersion Forces

  Temporary polarization of a nonpolar particle allows dispersion forces to form. The tendency of an electron cloud to distort is called its (polarizability).
• Ion-Dipole Interactions


  Found in solutions of ions. The strength of these forces is what makes it possible for ionic substances to dissolve in polar solvents.
• Viscosity


  Resistance of a liquid to flow. Increases with stronger intermolecular forces and decreases with higher temperature.
• Surface Tension


  Water acts as if it has a "skin" on it due to extra inward forces on its surface.
• Cohesion Forces


  Intermolecular forces that bind similar molecules to one another. Important in capillary action.
• Adhesive forces


  Intermolecular forces that bind a substance to a surface. Important in capillary action.
• Capillary Action


  The rise of liquids up narrow tubes. Adhesive forces attract the liquid to the wall of the tube. Cohesive forces attract the liquid to itself.
• Liquid Crystals


  Substances that do not go directly from the solid state to the liquid state, but have an intermediate state with some traits of solids and some of liquids.
• Types of Liquid Crystals


  • Nematic - molecules ordered in one dimension
  • Smectic - molecules ordered in two dimensions
  • Cholesteric - nematic-like crystals layered at angles
• Crystalline Solid


  Can form a regular repeating three-dimensional structure called a crystal lattice.
• Amorphous Solid


  Aggregates with no particular long-range order.
• Crystalline Solids


  • Arranged in fixed geometric patterns or lattices. The ordered arrangement maximizes the space they occupy and are essentially incompressible.
• Lattice


  A three-dimensional system of points designating the positions of the components (atoms, ions, or molecules) that make up a crystal. A unit cell is the smallest repeating unit of a lattice.
• Amorphous Solids


  • Have a random orientation of particles. Considered super-cooled liquids where molecules are arranged in a random manner similar to the liquid state.
• Phase Changes


  Conversion from one state of matter to another. Energy is either added or released.
• Heat of fusion


  Energy required to change a solid at its melting point to a liquid.
• Heat of vaporization


  Energy required to change a liquid at its boiling point to a gas.
• Heat of sublimation


  Energy required to change a solid directly to a gas.
• Heating Curves


  A plot of temperature vs. heat added. Within a phase, heat is the product of specific heat, sample mass, and temperature change. The temperature of the substance does not rise during a phase change. For the phase changes, the product of mass and the heat of fusion of vaporization is heat.
• Supercritical Fluids


  The state beyond the critical temperature and pressure where a gas cannot be compressed to a liquid.
• Vapor Pressure


  At any temperature, some liquid molecules have enough energy to escape the surface and become a gas. As the temperature rises, the fraction of molecules that have enough energy to break free increases.