L EWIS S TRUCTURES Lewis structures represent molecules or polyatomic ions by showing the position of atoms and balance electrons. Bonded (shared) electrons are represented by dashes and non-bonded (unshared) electrons are represented by dots.

R ULES 1. Count the number of atoms in the molecule or polyatomic ion and multiply by 8 (x 8). Recall that 8 valence electrons represent particular stability. There are several exceptions: a. Quantity of H atoms is multiplied by 2 b. Quantity of B atoms is multiplied by 6 c. Other exceptions exist

2. Calculate the total number of valence electrons each atom has prior to sharing. Note: When dealing with a polyatomic ion, the charge of the ion must be added to or subtracted from this total number of valence electrons. Positive ion, subtract Negative ion, add.

3. The number of electrons that must be shared is calculated by subtracting the result of Rule 2 from Rule The number of bonds in the structure is calculated by dividing the result of Rule 3 by 2. There will always be 2 electrons in each bond. 5. Draw dashes equal to the number of bonds to connect the atoms to the central atom. Note: Some structures do not have a central atom.

6. Place dots above all atoms, where applicable, to show their complete octet. Note: Hydrogen will only ever have one bond (1 dash); Boron can only have a maximum of 6 electrons surrounding it, so it may have any combination of dots and dashes to accomplish this. All other atoms will have any combination of dots and dashes to complete their octet (8).

#Formula Rule 1 Octet e - Rule 2 Valence e - Rule 3 Shared e - Rule 4 # Bonds Rule 5 & 6 Lewis Structure 1HBr 2 H2OH2OH2OH2O 3 (NO 3 ) 1- 4 CO 2 5 SO 3 6 (BrO 3 ) 1-