Lewis Structures

Question 1

What are Lewis Diagrams important representations of?

Answer 1

Important representations of what may or may not happen to electrons when a chemical reaction occurs

Question 2

What do Lewis Diagrams show?

Answer 2

• The connectivity (ionic/covalent) and type of covalent bonds (single, double, etc) that form between atoms
• Any non-zero formal charges and non-bonding electrons

Question 3

How do you calculate formal charges?

Answer 3

Fc = # of valence electrons - # of ‘things’ around the atom

Question 4

What are the steps to drawing the BEST Lewis Structure?

Answer 4

1. Difference in electronegativity to determine if an ionic or covalent bond is present
2. Valence electron count for all atoms
3. Skeletal Arrangement
4. Octet/Duet
5. Formal Charges
6. Best structure?

Question 5

What should you do for Step 1 of drawing Lewis Structures depending on the bond type?

Answer 5

• If ionic: do not draw bonds between atoms, because electrons are transferred
• If covalent: draw bonds between atoms because electrons are shared

Question 6

What should you do for Step 2 of drawing Lewis Structures depending on its charge?

Answer 6

• If the species has a + charge subtract electrons from the total amount
• If the species has a - charge add electrons to the total amount

Question 7

What are important things to consider in Step 3 of drawing Lewis Structures

Answer 7

• Atoms that can form the most bonds or have the lowest electronegativity are in the center (usually)
• Connect other atoms with single bonds

Question 8

What are important things to consider in Step 4 of drawing Lewis Structures if we have remaining electrons?

Answer 8

Use remaining electrons to complete octets/duets with lone pairs/multiple bonds

Question 9

What are important things to consider in Step 5 of drawing Lewis Structures

Answer 9

• Calculate formal charges for all atoms, and ensure they are minimized
• If they are not minimized, try adding double/triple bonds

Question 10

What are important things to consider in Step 6 of drawing Lewis’s Structures

Answer 10

• Do we have full octets?
• Is the formal charge minimized
• Is this the best connectivity

Question 11

What is the Octect/Duet Rule?

Answer 11

• Most atoms in a molecular or polyatomic ion attain a stable noble gas configuration of 8 electrons in its valence shell
• Full shell rule (or duet rule) for n=1 is 2 electrons

Question 12

What are the exceptions to the Octet Rule?

Answer 12

• If their formal charge is more stable without a filled octet (e.g BeCL2)
• Group 3 covalent bonds are fine without a filled octet if the formal charge is 0 (e.g BF3)
• Anything in n=3 or greater has the potential to expand its octet to the d-subshell

Question 13

What is an Isomer?

Answer 13

Compounds that have the same molecular formula but a different atom to atom connectivity

Question 14

Why is a condensed molecular formula useful?

Answer 14

• Gives you structural information and connectivity to help draw Lewis Structures