6: Shapes of molecules and intermolecular forces

• Linear?

  • Bonded regions=2
  • Lone pairs=0
  • Bond angle=180
• Non-linear?

  • Bonded regions=2
  • Lone pairs=2
  • Bond angle=104.5
• Trigonal planar?

  • Bonded regions=3
  • Lone pairs=0
  • Bond angle=120
• Pyramidal?

  • Bonded regions=3
  • Lone pairs=1
  • Bond angle=107
• Tetrahedral?

  • Bonded regions=4
  • Lone pairs=0
  • Bond angle=109.5
• Octahedral?

  • Bonded regions=6
  • Lone pairs=0
  • Bond angle=90
• Electronegativity?


  A measure of the attraction of a bonded atom for a pair of electrons in a covalent bond

  Affected by:

  • Nuclear charge
  • Atomic radius
  • Electron shielding
• Polar?


  When the bonding atoms are different one of the atoms is likely to attract the bonding electrons more
• Non polar?


  The electrons in the bond are evenly distributed
• Intermolecular forces?

  • Permanent dipole-dipole
  • Induced dipole-dipole (London)
  • Hydrogen bonds
• Permanent dipole-dipole forces?


  A small charge difference across a bond that results from a difference in the electronegativities of the bonded atoms

  • In polar molecules
  • Permanent dipole-dipole interactions between different molecules attract each other to form weak permanent dipole-dipole interactions
• Induced dipole-dipole interactions (London forces)?

  Movement of electrons temporarily unbalances the distribution of the charge leading to temporary induced dipoles which can induce dipoles in neighbouring molecules

  • weakest intermolecular force
  • In polar and non polar molecules
• Hydrogen bonding?


  A strong dipole-dipole attraction between an electron deficient hydrogen atom on one molecule and a lone air of electrons on a highly electronegative atom on a different molecule
• Simple molecular substance?


  A substance made up of simple molecules containing a definite number of atoms with a definite molecular formula

  In the solid state, simple molecular molecules form a simple molecular lattice as molecules are held together by weak intermolecular forces (but atoms within the molecules are bonded together strongly by covalent bonds)