chapter 6 - shapes of molecules and intermolecular forces

• What is the shape of the molecule with 2 bonded pairs of electrons?

  Linear
• What is the bond angle for linear shapes?

  180
• What is the shape of the molecule with 3 bonded pairs of electrons?

  Trigonal planar
• What is the bond angle for a trigonal planar shape?

  120
• What is the shape of the molecule with 4 bonded pairs of electrons?

  Tetrahedral
• What is the bond angle for a tetrahedral shape?

  109.5
• What is the shape of the molecule with 5 bonded pairs of electrons?

  Trigonal bypyramidal
• What is the bond angle for trigonal bypyramidal shape?

  90 and 120
• What is the shape of the molecule with 6 bonded pairs of electrons?

  Octahedral
• Definition of electronegativity:

  = the attraction of a bonded atom for the pair of electrons in a covalent bond
• In molecules with the same elements…

  … e.g H2, the bonded electron pair is shared evenly
• What influences electronegativity when the bonded atoms are different elements?

  • different nuclear charges
  • different sized atoms
  • shared pair of electrons may be closer to one nucleus than the other
• What is the scale used to measure electronegativity?

  the pauling scale
• What atom is the most electronegative?

  fluorine
• Why are the noble gases not included in the pauling scale?

  as they tend not to form compounds
• What 4 elements have the most electronegative atoms?

  • nitrogen
  • oxygen
  • fluorine
  • chlorine
• What 3 elements have the least electronegative atoms?

  • lithium
  • sodium
  • potassium
• How can the electronegativity be used to predict the type of bonding?

  • electronegativity values above 1.8 tend to be ionic as they a relatively large values
• When will a bond be non-polar?

  • the bonded atoms are the same

  or

  • the bonded atoms have the same or similar electronegativity
• What are the 3 main types of intermolecular forces?

  • induced dipole-dipole interactions (london forces)
  • permanent dipole-dipole interactions
  • hydrogen bonding
• London forces:

  • weakest type of intermolecular force
  • they exist between all molecules whether they are polar or non-polar
  • movement of electrons —> electron repulsion causes electrons to move to the furthest side away
• Permanent dipole-dipole forces…

  … exist between polar molecules.
• Solubility of non-polar and polar simple molecular substances:

  • non-polar substances are soluble in non-polar solvents
  • polar substances are soluble in polar solvents
• Can simple molecules conduct electricity? and why?

  • no
  • there are no mobile charge carriers
• Hydrogen bonding:

  • strongest out of the three
  • can form between oxygen + nitrogen (+ fluorine)
  • the hydrogen bond acts between a loan pair of electrons on electronegative atom in one molecule and a hydrogen atom in a different molecule
• Anomalous properties of water:

  1. ice is less dense than water
  2. water has a relatively high mp + bp
• Why is ice less dense than water?

  • hydrogen bonds hold water molecules in open lattice structure
  • water molecules in ice are further apart than in water
• Why does water have a relatively high mp + bp?

  • hydrogen bonds = strong
  • lots of energy needed to overcome them