Covalent Bonding 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 N 2 H 4

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  Δ H = Δ H (bonds broken) - Δ H (bonds formed)  BUT ! ! !  Δ H ≈ Σ (BE) reactants - Σ (BE) products

Example 1:  Calculate the enthalpy of formation for hydrazine (N 2 H 4 ) using bond energies.

Example 2:  Using the following equation: C 2 H 6 + Cl 2 C 2 H 5 Cl + HCl Calculate the Δ H rxn.