Given the following bond lengths, explain the bonds in terms of bond evergy and the relationsip between locations of atoms on the periodic table.

Question

Bond    Bond Length

C-O     143

C-C     154

C-Cl    177

C-I      214

Answer 1

The reason that this is a difficult question is because there are many contributing factors to bond strength. In general, bond strength is due to the following factors: electronegativity difference between the atoms, the presence of a double or triple bond, and the energy required to break the  bond.

 

Electronegativity is the  ability of the atom to pull the electrons closer to itself. There is a  bigger electronegative difference between  a metal and nonmetal, such as LiCl. As   a metal, lithium wishes to give away  its electron in order to become an octet and Chlorine wishes to take  lithium's electron in order  to become  an octet. Furthermore, if you move  up to the group from  chlorine to fluorine  you would see an even greater electronegative  difference. As you move up in a group there is an increase in electronegativity or an atom's desire to pull of an electron closer to itself.  A higher electronegativity reduces a bond length. Thus, in your example, C- Cl can be assumed to be a stronger bond than C-I due to  the increase in electronegativity going up the group and the shorter bond length that is observed in C-Cl.

A triple bond is stronger than a double bond. A double bond is stronger than single bond. Thus, when  a triple bond is shared over a single bond, we  can assume that the bond is much shorter because more electrons are shared.  In conclusion,   if we compared C-0 (carbon monoxide)  to the other bond it would be  shorter than any of  the others due to its triple bond being  shared. This means  that its most likely to have a higher bond energy than the other options. Although, we would need to do the math to confirm with the bond dissociation energies. In addition,  C-C  have no electronegativity difference because the atoms are the  same and cancel each other out, but  the atoms share a double dond. This makes the C-C shorter and more energetic than the C-Cl and C-I, but not as strong as C-O triple bond. It can also be difficult  breaking a C-C bond because  the electrons are equally   shared and there is not a real dipole  making it less  of an ionic bond like C-I or C-Cl.

 

Overall, the most reliable factor at a glance to determine if the bond is stronger than another is calculating  the bond dissociation values.  Bond dissociation energies  are directly proportional to the bond strength. The more energy required to break the bond the stronger the bond is. Bond dissociation energies account for the increase in the energy  of  a molecule due to the increase in bonding (  triple, double and single bond length). Fortunately, the shortness in bond length tends to be inversely related to the bond  energies and the bond dissociation energies.

 

Hope this helps!