Lewis Structures

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

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

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

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

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

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

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.

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

Practice Problems Hydrogen cyanide, HCN

Practice Problems Nitrate ion

Practice Problems Acetylene, C2H2

Practice Problems Carbon dioxide

Practice Problems R-134a, CF3CH2F

Practice Problems Nitrite ion