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
- Identify central atom → usually element that is drawn first and there is only one of
- Find the total number of valence e-
- Divide this number in half = # of available bonding pairs
- Draw a “frame” using single bonds from the central atom to surrounding atoms
- 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
- 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
- C, N, O, and F and other 2nd row elements always obey the octet rule
- B and Be often have less than 8 e- around them
- 3rd row and heavier elements can exceed the octet rule by using their empty valence d orbitals
- Hydrogen obeys the duet rule