Module 2) 6: Shapes of Molecules and Intermolecular forces

• What theory explains the shapes of molecules and ions?

  Electron-pair repulsion theory
• Why do electron pairs repel one another?

  Because they have negative charges
• What determines the shape of a molecule or ion?

  Electron pairs surrounding a central atom
• How do electron pairs arrange themselves in a molecule?

  As far apart as possible
• What is the bond angle in a methane molecule?

  109.5°
• What shape does a methane molecule have?

  Tetrahedral
• What do wedges represent in molecular diagrams?

  Three-dimensional bond orientations
• How does a lone pair affect bond angles?

  It decreases the bond angle
• What is the bond angle reduction for each lone pair?

  About 2.5°
• How many bonding regions does carbon dioxide have?

  Two bonding regions
• What shape does carbon dioxide have?

  Linear
• What shape does boron trichloride have?

  Trigonal planar
• What shape does sulfur hexafluoride have?

  Octahedral
• How many electron pairs does sulfur hexafluoride have?

  Six electron pairs
• What is the bond angle in an octahedral shape?

  90°
• What is the shape of the ammonium ion?

  Tetrahedral
• How many bonded pairs does the ammonium ion have?

  Four bonded pairs
• What shape do carbonate and nitrate ions have?

  Trigonal planar
• What shape does the sulfate ion have?

  Tetrahedral
• What does VSEPR theory help predict?

  The shapes of molecules and ions
• What is electronegativity?

  Attraction of an atom for shared electrons
• What scale is used to measure electronegativity?

  Pauling scale
• Which element has the highest electronegativity?

  Fluorine
• What happens to electronegativity across the periodic table?

  It increases across and up
• What type of bond forms with a large electronegativity difference?

  Ionic bond
• What characterizes a non-polar covalent bond?

  Equal sharing of electrons
• What is a polar covalent bond?

  Asymmetrical sharing of electrons
• What charge does chlorine have in hydrogen chloride?

  Partial negative charge (δ−)
• What does a dipole indicate in a molecule?

  Permanent charge separation
• What is the bond angle in water?

  Approximately 104.5°
• What are the shapes and bond angles for molecules with different numbers of electron pairs?

  • 2 electron pairs: Linear, 180°
  • 3 electron pairs: Trigonal planar, 120°
  • 4 electron pairs: Tetrahedral, 109.5°
  • 6 electron pairs: Octahedral, 90°
• What are the shapes of common molecules and ions?

  • Methane (CH₄): Tetrahedral, 109.5°
  • Ammonia (NH₃): Trigonal pyramidal, < 109.5°
  • Water (H₂O): Bent, < 104.5°
  • Carbon dioxide (CO₂): Linear, 180°
  • Boron trichloride (BCl₃): Trigonal planar, 120°
  • Sulfur hexafluoride (SF₆): Octahedral, 90°
• What are the characteristics of polar and non-polar bonds?

  • Non-polar bonds: Equal sharing of electrons, symmetrical
  • Polar bonds: Asymmetrical sharing of electrons, different electronegativities
• What are the key points of electronegativity?

  • Attraction of an atom for shared electrons
  • Measured using the Pauling scale
  • Increases across and up the periodic table
  • Fluorine is the most electronegative
• How does electronegativity affect bond type?

  • Large difference: Ionic bond
  • Small difference: Polar covalent bond
  • No difference: Non-polar covalent bond
• What is the significance of dipoles in polar molecules?

  • Indicates permanent charge separation
  • Affects molecular interactions and properties
• What is the term for the measure of an atom's ability to attract electrons?

  Electronegativity
• What type of bond is formed when electrons are shared unequally between atoms?

  Polar covalent bond
• Give an example of a polar covalent bond.

  Hydrogen chloride, HCl
• What happens to the shared electron pair in a polar covalent bond?

  It is pulled closer to the more electronegative atom.