Lewis Structures

Question 1

What is a lewis structure

Answer 1

• lewis structures are structures in which covalent bonds are denoted by lines (or dots) connecting atoms and lone pairs (when relevant) are shown
• they are simplistic but can satisfactorly show atom connectivity
• down side is they are visually cluttered and drawing each H can make it hard to see which is why skeletal drawings are often preferable

Question 2

Step one of drawing

Answer 2

1. draw out the molecular framework (skeleton) - think of a carbon framework, orient atoms around carbon atoms

Question 3

Step two of drawing

Answer 3

2. total up the number of valence electrons
   - atoms each contribute a certain amount of valence electrons when they engage in a covalent bonding interaction
   - use PT for valence electron number

Question 4

Step three in drawing

Answer 4

3. connect the atoms in your molecular framework with bonds and add lone pairs to heteroatoms

Question 5

Step four in drawing

Answer 5

4. count the number of electrons in the proposed lewis structure and compare this to the number of valence electrons in step 2
   - each lone pair is 2 electrons
   - each dash line (bond) is 2 electrons
   - if the number matches, the structure is correct

Question 6

If the number of electrons from step 2 don’t match step 4 then….

Answer 6

• make sure you didn’t add one too many lone pairs or bonds
• try adding a double bond and recount
• if the number is still incorrect, add a triple bond