1. Chapter 6 Molecules and Covalent Compounds
6.3
Multiple Covalent Bonds and Resonance
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

2. Multiple Bonds In a single bond, One pair of electrons is shared.
In a double bond,
Two pairs of electrons are shared.
In a triple bond,
Three pairs of electrons are shared.

3. Electron-Dot Formula of`CS2
Write the electron-dot formula for CS2.
STEP 1 Determine the atom arrangement. The C atom is the central atom. S C S
STEP 2 Add the valence electrons for 1C and 2S.
1C(4e-) + 2S(6e-) = 16e-

4. Electron-Dot Formula CS2
STEP 3 Attach each S atom to C with one electron pair.
S : C : S
Calculate the remaining electrons.
16e e- = 12e- left

5. Electron-Dot Formula CS2
STEP 4 Attach 12 remaining electrons as 6 lone pairs
to complete octets.
: S : C : S :
STEP 5 To complete octets, move two lone pairs
between C and S atoms to give two double bonds.
: S : : C : : S : or : S = C = S : `

6. Multiple Bonds in N2 In nitrogen N2,
Octets are achieved by sharing three pairs of electrons, which is a triple bond.

7. Some Electron-Dot Formulas

8. Resonance Structures Resonance structures are:
Two or more electron-dot formulas for the same arrangement of atoms
Related by a double-headed arrow
Written by changing location of a double bond from the central atom to a different attached atom
Sometimes written as a hybrid resonance structure

9. Resonance Structures :O : :O: :O: :O : :O: :O:
Resonance structures for NO3− are:
−   −   −
:O: :O: :O:
║ │ │
N N N
:O : :O: :O: :O : :O: :O:
       

10. Learning Check
Carbonate has three resonance structures. If the following is one, what are the other two? 2-
:O: C
:O: :O:
   

11. Solution :O : :O: :O: :O : :O: :O:
Carbonate has three resonance structures. If the following is one, what are the other two?
2−   2−   −
:O: :O: :O:
│ │
C C C
:O : :O: :O: :O : :O: :O:
       

12. Writing Resonance Structures
Cyanate ion NCO− has three resonance structures.
STEP 1 Write the arrangement of atoms. N C O −
STEP 2 Count the valence electrons.
1N(5e−) + 1C(4e−) + 1 O(6e−) + charge (1e−) = 16e−
STEP 3 Connect bonded atoms by single electron pairs. N: C :O − 4e− used
Determine the remaining electrons.
16e− - 4e− = 12e−

13. Writing Resonance Structures
STEP 4 Add 12 remaining electrons as 6 lone pairs.
    −
: N─C─O :
   
STEP 5 Form double or triple bonds to make octets.
    −   −   −
:N=C=O: :N─CO: :NC─O:
   

14. Learning Check
Write two resonance structures for nitrite NO2−.

15. Solution :O=N─O: :O─N=O: NO2− = 18 e− Electron-dot formula
      −
: O─N─O :
   
Using a double bond to complete octets gives two
resonance structures.
      −       −
:O=N─O: :O─N=O:
   