Bond Energy

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

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

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

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

C C C C C = C C C C – C

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

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

C–N 305 C–O 360 C–F 484

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

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

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

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

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

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