Covalent
Bonding
Formal Charges
Bond Lengths
Bond Energies
 Not all chemical bonds have the same
strength
 vary based on atom combination and the amount
of shared electrons between atoms
**More electrons in a chemical bond, atoms held
more tightly**
Bond Length
 Deals with covalent bonds only
 Distance between nuclei of 2 atoms in a chemical
bond
 Dependent on atom type and bond order
  bond # (double, triple, etc.),  bond length
 = Σ covalent radii of 2 atoms
Example 1:
 Estimate the bond length of the nitrogen-nitrogen
bond in N2H4
Example 2:
 Estimate the bond length for BrCl
Bond Energy
 Chemical bonds constantly breaking/forming
 Breaking bond—energy absorption
 Bond formation—energy release
 Bond Dissociation Energy (kJ/mol)
 Amount of energy needed to break ONE mole of
covalent bonds existing between 2 atoms

How are bond energy
and bond order related to
each other?
 Increase bond order, increase bond dissociation energy
 Neighboring atoms close to bond can influence dissociation
energy
 SOOOOOOO
Bond Energy (cont.)
 Average Bond Energy
 Average dissociation energies for molecules with a
specific bond
 ΔH = ΔH (bonds broken) - ΔH (bonds formed)
 BUT ! ! !
 ΔH ≈ Σ (BE) reactants - Σ (BE) products
Example 1:
 Calculate the enthalpy of formation for hydrazine
(N2H4) using bond energies.
Example 2:
 Using the following equation:
C2H6 +
Cl2
Calculate the ΔH rxn.
C2H5Cl
+ HCl
Homework
 Read pp. 366- 370
 Problems #63, 64, 67, 68, 69, 70, 71, 72, 98