1. Bond Energy

2. 8.14 – Bond Energy Bond energy: the measure of bond strength
the stronger the bond, the higher the bond energy
expressed as heat required to break 1 mole of molecules

4. It takes energy to break bonds, and energy is released when bonds are formed

5. breaking required making released Example:
The reaction turning 1 molecule of H2(g) into two H(g) atoms involves bond _______________. Energy is ______________.
The reaction turning two oxygen atom into a molecule of O2 involves bond _______________. Energy is ______________.
Compare the bond energies of single, double, and triple bonds. Explain the data.
Compare the bond energies of C-N, C-O, C-F. Explain the data.
breaking
required
making
released

7. breaking required making released Example:
The reaction turning 1 molecule of H2(g) into two H(g) atoms involves bond _______________. Energy is ______________.
The reaction turning two oxygen atom into a molecule of O2 involves bond _______________. Energy is ______________.
Compare the bond energies of single, double, and triple bonds. Explain the data.
Compare the bond energies of C-N, C-O, C-F. Explain the data.
breaking
required
making
released

9. C C
C C
C = C
C C
C – C

10. breaking required making released Example:
The reaction turning 1 molecule of H2(g) into two H(g) atoms involves bond _______________. Energy is ______________.
The reaction turning two oxygen atom into a molecule of O2 involves bond _______________. Energy is ______________.
Compare the bond energies of single, double, and triple bonds. Explain the data.
Compare the bond energies of C-N, C-O, C-F. Explain the data.
breaking
required
making
released
Triple > double > single
More e- shared = more attractive forces between 2 nuclei

12. breaking required making released Example:
The reaction turning 1 molecule of H2(g) into two H(g) atoms involves bond _______________. Energy is ______________.
The reaction turning two oxygen atom into a molecule of O2 involves bond _______________. Energy is ______________.
Compare the bond energies of single, double, and triple bonds. Explain the data.
Compare the bond energies of C-N, C-O, C-F. Explain the data.
breaking
required
making
released
Triple > double > single
More e- shared = more attractive forces between 2 nuclei
C-F > C-O > C-N

14. C–N
C–O
C–F

15. breaking required making released Example:
The reaction turning 1 molecule of H2(g) into two H(g) atoms involves bond _______________. Energy is ______________.
The reaction turning two oxygen atom into a molecule of O2 involves bond _______________. Energy is ______________.
Compare the bond energies of single, double, and triple bonds. Explain the data.
Compare the bond energies of C-N, C-O, C-F. Explain the data.
breaking
required
making
released
Triple > double > single
More e- shared = more attractive forces between 2 nuclei
C-F > C-O > C-N
Bond strength increases with increasing electronegativity and decreasing radius

16. Bond length: the distance between 2 nuclei of a molecule
The shorter the bond length, the stronger the bond, the higher the bond energy
Example: How do the bond lengths of single, double, and triple bonds compare with each other?
C C
C C
C C
0.120 nm
0.134 nm
0.154 nm

17. LiF LiCl LiBr Electronegativity: F > Cl > Br
Example: Rank the following compounds in order of increasing melting point (increasing bond strength).
LiF LiCl LiBr
Electronegativity: F > Cl > Br
bond strength LiF > LiCl > LiBr
melting point LiF > LiCl > LiBr
845°C
605°C
552°C

18. Example: Which of the following compounds has the higher bond energy?
NaCl MgO
MgO is being held together by 2+ and 2- charge as opposed to 1+ and 1- in NaCl
801°C
2852°C

19. higher stronger higher higher higher
For ionic compounds, two things must be considered in order to determine bond strength. They are (in order of importance):
The charge: the ___________ the charge on each ion in the ionic compound, the ______________ the ionic bond, the ___________ the bond energy.
Electronegativity: the higher the electronegativity of the non-metal, the _______________ the attraction, the ______________ the bond energy.
higher
stronger
higher
higher
higher

20. How do you know if a bond is strong?
Covalent Compounds
Number of bonds: more bonds = strong bond
Atomic radii: short bond length = strong bond
Electronegativity: strong electronegativity = strong bond
Ionic Compounds
Charge: high charge = strong bond
Electronegativity of non-metal: high electronegativity = strong bond