Covalent Bonding Bond LengthsBond 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 C2H5Cl + HCl

Calculate the ΔH rxn.