CHAPTER 6: Shapes of molecules and Intermolecular Forces

• What determines the shape of a simple molecule or ion?

  The number of electron pairs around the central atom
• How do electron pairs affect bond angles in molecules?

  They repel each other to maximize bond angles
• What does a solid line in molecular diagrams indicate?

  A bond in the plane of the paper
• What does a wedged line in molecular diagrams indicate?

  A bond coming out of the plane of the paper
• What does a dotted line in molecular diagrams indicate?

  A bond going into the plane of the paper
• How do lone pairs affect bond angles?

  They provide additional repulsive forces
• How much does each lone pair reduce the bond angle?

  By 2.5 °
• What are the steps to determine the shape of a molecule?

  1. Find the number of electron pairs.
  2. Determine bonding and lone pairs.
  3. Identify basic shape and additional repulsion.
• What are some common molecule shapes and their bond angles?

  • Linear: 180° (2 bonding pairs, 0 lone pairs)
  • Bent: 104.5° (2 bonding pairs, 2 lone pairs)
  • Trigonal Planar: 120° (3 bonding pairs, 0 lone pairs)
  • Triangular Pyramid: 107° (3 bonding pairs, 1 lone pair)
  • Tetrahedral: 109.5° (4 bonding pairs, 0 lone pairs)
  • Trigonal Bipyramid: 180° and 120° (5 bonding pairs, 0 lone pairs)
  • Octahedral: 90° (6 bonding pairs, 0 lone pairs)
• What is electronegativity?

  The ability to attract bonding electrons
• How does electronegativity change across a period?

  It increases as atomic radius decreases
• How does electronegativity change down a group?

  It decreases as shielding increases
• What does a higher Pauling electronegativity value indicate?

  A greater electronegativity
• Which atom is the most electronegative?

  Fluorine
• What does a greater electronegativity difference indicate?

  A greater bond polarity
• What is a permanent dipole?

  A polar bond with unequal charge distribution
• Why is hydrogen fluoride considered a polar molecule?

  Fluorine is more electronegative than hydrogen
• What is required for a molecule to be polar?

  Polar bonds with non-canceling dipoles
• Why is CO₂ considered non-polar despite having polar bonds?

  Dipoles cancel due to linear shape
• What can polar molecules with permanent dipoles form?

  A lattice of molecules similar to ionic lattice
• What is an induced dipole?

  When electron orbitals are influenced by another particle
• What are the three main types of intermolecular forces?

  1. London Forces
  2. Permanent Dipole
  3. Hydrogen Bonding
• What are London forces?

  The weakest type of intermolecular force
• How does the strength of London forces vary?

  It varies with the molecular mass, number of electrons and shape
• How do straight chain molecules compare to branched chain molecules in terms of London forces?

  Straight chains experience stronger forces
• What happens to boiling points as alkane chain length increases?

  Boiling points increase due to stronger forces
• How does branching affect London forces?

  It weakens the forces between chains
• What is a permanent dipole in intermolecular forces?

  Attraction between molecules with polar bonds
• Why do substances with permanent dipoles have higher melting and boiling points?

  More energy is needed to overcome stronger interactions
• What are hydrogen bonds?

  The strongest type of intermolecular force
• Between which atoms do hydrogen bonds occur?

  Hydrogen and nitrogen, oxygen, or fluorine
• How do hydrogen bonds form?

  Through lone pairs on electronegative atoms
• How do hydrogen bonds affect the physical properties of substances?

  They increase melting and boiling points
• Why does water have high melting and boiling points?

  Due to the presence of hydrogen bonds
• Why does ice have a lower density than liquid water?

  Hydrogen bonds create a rigid structure

  
• Why do alcohols have higher boiling points than alkanes?

  Alcohols can form hydrogen bonds
• What role do hydrogen bonds play in solvents like alcohol and water?

  They allow dissolving of hydrogen-bonding compounds
• Where are hydrogen bonds found in DNA?

  Between base pairs AT and GC
• What are the characteristics of simple molecular substances?

  • Consist of covalently bonded molecules
  • Held together by weak London forces
  • Have low melting and boiling points
  • Very poor conductors due to lack of charged particles
• What are the characteristics of macromolecular structures?

  • Covalently bonded into a giant lattice
  • Very high melting points
  • Rigid due to strong covalent bonds