the shapes of molecules and ions

• What does molecular shape depend on?

  Electron pair arrangement
• How does the three-dimensional shape of a molecule depend on its central atom?

  It depends on the number and arrangement of electron pairs
• What are the two categories of electron pairs?

  Bonding pairs and lone pairs
• What are bonding pairs involved in?

  Forming covalent bonds with other atoms
• What are lone pairs not involved in?

  Bonding and remain on the central atom
• What is the significance of the ammonia molecule (NH3) in terms of electron pairs?

  • Four electron pairs around nitrogen
  • Three bonding pairs with hydrogen
  • One lone pair on nitrogen
• What does the electron pair repulsion theory state?

  A molecule adopts a shape that minimizes repulsion
• What causes electron pairs to repel each other?

  Their negative charge
• Why do lone pairs cause more repulsion than bonding pairs?

  Because they are closer to the nucleus
• How do electron pairs arrange themselves to minimize repulsion?

  As far apart as possible
• What is the order of repulsion strength among electron pairs?

  • Lone pair-lone pair > Lone pair-bonding pair > Bonding pair-bonding pair
• How do lone pairs affect bond angles in a molecule?

  They compress bond angles
• What is the first step to predict the shape of a molecule or ion?

  Determine the total number of electron pairs
• How do you find the number of outer shell electrons of the central atom?

  Using its group number
• What do you add for each bonded atom when determining electron pairs?

  Add one electron for each bonded atom
• How do you adjust the electron count for ions?

  Add or subtract electrons based on charge
• How do you calculate the number of electron pairs from total electrons?

  Divide the total number of electrons by two
• How do you determine the number of lone pairs?

  Subtract the number of bonds from electron pairs
• How can molecular shapes be predicted based on electron pairs?

  • Linear
  • Trigonal planar
  • Tetrahedral
  • Trigonal pyramidal
  • Bent
  • Trigonal bipyramidal
  • Seesaw
  • T-shaped
  • Octahedral
  • Square planar
• How should multiple bonds be treated when determining molecular shape?

  Treat each multiple bond as a single electron pair
• What is the shape and bond angle of carbon dioxide (O=C=O)?

  Linear with a 180° bond angle
• What is the shape and bond angle of ethene (H2C=CH2)?

  Trigonal planar with 120° bond angles