Resonance

Question 1

What is bond length?

Answer 1

Distance between the nuclei of two atoms in a bond

Question 2

What does bond length depend on?

Answer 2

• The size of the atoms involved in the bond
• The larger the atoms involved, the larger the bond length

Question 3

What are the three characteristics of bonds?

Answer 3

Bond length, bond order, and bond strength

Question 4

What is Bond Order?

Answer 4

Based on the number of electrons shared between atoms

Question 5

How do you calculate bond order?

Answer 5

• For bonds not including resonance the bond order is the bond (e.g single bond = bond order of 1
• For bonds that participate in resonance: #of bonds at that point / by the two structures

Question 6

What happens to bond length if bond order increases?

Answer 6

As bond order increases, bond length decreases

Question 7

What is bond strength/bond dissociation energy?

Answer 7

• The energy required to break a bond
• The shorter a bond the stronger the bond

Question 8

As bond order increases, what happens to bond strength?

Answer 8

Bond strength increases

Question 9

What is resonance?

Answer 9

• The movement of electrons over the skeletal arrangement at atoms
• Some of the electrons in a resonance structures are delocalized
• Can move the non-skeletal electrons

Question 10

What things to consider for resonance?

Answer 10

• Formal charges can be moved
• Single bonds in the skeleton are not broken
• Nuclei don’t move
• Atoms remain connected in the same skeletal arrangement

Question 11

3 things to check the validity of resonance structures?

Answer 11

• Electron count has not changed
• Formal charges are correct
• The sum of formal charges is equal to the formal charge for the species

Question 12

What are the 5 steps to drawing a Resonance Hybrid

Answer 12

1. Draw all equivalent resonance structures
2. Ensure the skeleton stays the same between structures
3. Use dotted lines for bond moving between atoms
4. Calculate the formal charges (adding charges together gives the overall formal charge)
5. Bond orders

Question 13

What do Curly arrows show?

Answer 13

• Movement of electrons in resonance and reactions
• Flow in a single overall direction

Question 14

What do reaction mechanisms show?

Answer 14

• Shows how electrons move (not atoms) in making and breaking bonds when going from reactants and products
• Always have a region of high electron density attacking a region of low electron density

Question 15

What are regions of high electron density?

Answer 15

• They are attacking
  1. Negative formal charge
  2. Most electronegative atoms in polar bond

Question 16

What are regions of low electron density?

Answer 16

• Gets attacked
  1. Positive formal charge
  2. Least electronegative atom in polar bond