Shapes Of Molecules

Shapes Of Molecules

1. Molecules with lone pairs

   • Pyramidal
     • These molecules have 1 lone pair and 3 bonding pairs of electrons
       • Examples are: Ammonia(NH3) - Bond angle of 107 degrees
   • Non-Linear/Bent
     • These molecules have 2 lone pairs and 2 bonding pairs of electrons
       • Examples are: Water(H2O) - Bond angle of 104.5 degrees
   • If a molecule is tetrahedral, 1 lone pair will make it pyramidal
     • Adding another lone pair to this will result in a non-linear/bent shape
   • A lone pair of electrons is more electron dense than a bonded pair
     • As such, each lone pair reduces the bond angle by about 2.5 degrees

2. Molecules without lone pairs

   • Linear
     • These molecules have 2 bonding pairs of electrons
       • Examples are: H2 or CO2 - Bond angle of 180 degrees
   • Trigonal Planar
     • These molecules have 3 bonding pairs of electrons
       • Examples are: BF3 - Bond angle of 120 degrees
   • Trigonal Bipyramid
     • These molecules have 5 bonding pairs of electrons
       • Examples are: PCl5 - Bond angles of 90 and 120 degrees
         • The angle between the vertical bond and horizontal bond is 90 degrees. However, the angle between each horizontal bond is 120 degrees
   • Octahedral
     • These molecules have 6 bonding pairs of electrons
       • Examples are: SF6 - Bond angle of 90 degrees
   • Tetrahedral
     • These molecule have 4 bonding pairs of electrons
       • Examples are: Methane - CH4 - Bond angle of 109.5 degrees

3. Shapes of ions

   • The principles about molecular shapes can be applied to ionic shapes
   • As such in the example of an ammonium ion - NH4, the shape is tetrahedral
     • Thus meaning that it has 4 bonding pairs of electrons
       • However, it will also need to be surrounded by square brackets and have the displayed charge as it is an ionic molecule