Lewis Structure for Ions

  • Rule: only the valence electrons are included → Metal cation won’t have any dots

Lewis Structure for Molecules with Covalent Bonds

How to Draw Lewis Structures

  1. Identify central atom → usually element that is drawn first and there is only one of
  2. Find the total number of valence e-
  3. Divide this number in half = # of available bonding pairs
  4. Draw a “frame” using single bonds from the central atom to surrounding atoms
  5. Subtract pairs used in step 4 from total pairs in step 3 = # of lone pairs
  • Lone pairs are placed around terminal atoms first → any remaining pairs are assigned to the central atom
  1. If the central atom is not surrounded by four electron pairs, convert 1 or 2 of the lone pairs from the terminal atoms to a double of triple bond between the terms atom and the central atom
  • In some cases there will be resonance

Review and Exceptions to the Octet Rule

  1. C, N, O, and F and other 2nd row elements always obey the octet rule
  2. B and Be often have less than 8 e- around them
  3. 3rd row and heavier elements can exceed the octet rule by using their empty valence d orbitals
  4. Hydrogen obeys the duet rule