Unit+2+-+Lewis+Dot+Diagrams

1. Determine the number of valence electrons available for bonding from each element in the compound. Ex. **CO², 1C+2O = 1(4) + 2(6) = 16 valence electrons**
 * Rules:**

2. Determine the central atom which usually is the **LEN** or least electronegative of the elements, cannot be hydrogen, is usually the first element listed in the chemical equation, and typically found farther left in the periodical table. In this case it would be **C.** All other elements will be terminal.

3. Arrange the remaining elements around the central atom. Ex. **O C O**

4. Determine the number of available bonding pairs by dividing the number of available valence electrons by **2**. In this case there are a total of **8 bonding pairs/lone pairs**.

5. Place a bonding pair between the central atom and each of the terminal atoms. Ex. **O - C - O** 6. Subtract the number of pairs used ( **8 - 2 = 6** ) from the total number of pairs. Whatever is left is used for lone pairs. You add these to the terminal atoms to satisfy their octets. Anything else goes to the central atom. When in doubt, always place lone pairs on the most electronegative atoms. If the central atom does not have 8 valence electrons/ 4 bonding pairs in its octet, you need to convert lone pairs into double or triple bonds. 7. All elements should "feel" as if they have 8 valence electrons.

8. There are exceptions to the octet rule. Some compunds do not have enough valence electrons to make complete octets so you really only need to have enough for single bonds between the atoms, leftovers go on the central atom, then you call it a day. Sometimes you'll have too many electrons on the central atom, this is referred to as hypervalent. 9. Sometimes compounds that have double/triple bonds can be drawn in different ways, this means that the compound is "resonating". The negative charge is moving along through all the bonds in the compound to even out the negative polar charge from the multiple bond(s). **Ex.** *cyclohexane Partial Charges in Lewis Dot Diagrams ** 10. When a diagram has a + or - charge on the outside of the brackets, this means that the compound either has extra or is lacking electrons. For some extra practise with completing Lewis Diagrams or Resonance structures, try [|ChemPractise.com].
 * Resonance **