1. Lewis Structures

2. Lewis Structures
How the atoms in covalent compounds are hooked together.
Similar to Lewis Dot Diagrams
Must follow a set of rules to get the Lewis Structure

3. The RULES 1. Add up the number of valence electrons in the compound
2. Guess at a structure and hook the atoms together using single bonds
A) Usually the first element is in the middle
B) Usually the most metallic element is in the middle
3. Give all atoms on the outside an octet
4. If you have electrons left over after step 3 then add all of them to the central atom
5. If you don’t have enough electrons to give the central atom an octet
A) Check for deficient atoms (Be, B, Al)
B) Try a double bond
C) Try a triple bond

4. HINTS
Leave a big gap in your notes for a list of hints

5. Practice Problems Carbon tetrachloride CCl4
HINT: Carbon is almost always in the middle

6. Practice Problems Ammonia NH3
HINT: Hydrogen only needs two electrons to get an “octet”

7. Practice Problems Sulfur hexafluoride SF6
HINT: Some central atoms can have more than an octet of electrons. S and P do this often.

8. Practice Problems Boron trihydride BH3
There is no way Boron can have an octet
HINT: Boron, Beryllium, and Aluminum very rarely have an octet of electrons.

9. Practice Problems Formaldehyde, CH2O Which structure is correct?
HINT: The most symmetric structure is usually the correct one.

10. Practice Problems
Hydrogen cyanide, HCN

11. Practice Problems
Nitrate ion

12. Practice Problems
Acetylene, C2H2

13. Practice Problems
Carbon dioxide

14. Practice Problems
R-134a, CF3CH2F

15. Practice Problems
Nitrite ion