Electronegativity and Bond Strength

[Emily Huang 2A]

I had a question regarding Problem 3.87 in the textbook:

Which do you predict to have the strongest CX bond, where X is a halogen: (a) CF4, (b) CCl4, or (c) CBr4? Explain.

I understand that the answer is CF4 because of the small size of the fluorine atom and the short bond lengths, but the solution manual also says that "note that electronegativity and polarity arguments would predict the C--F bond to be the weakest." I don't really understand this statement, but I'm aware that the electronegativity difference between C and F should be extremely high. How does this high electronegativity difference cause the bond to be weak?

[Jeannie Huang 3B]

I think the reason for this is that when the electronegativity difference is high, the electrostatic attraction between the positive and negative charges will also be high, causing a shorter bond length. The bond also takes on an increasingly ionic character. I'm not sure, however, if ionic compounds always exhibit stronger bonds than covalent compounds.

[Asia Yamada 2B]

C—F bonds have the smallest electronegativity difference which means that the C—F bond is the least polar out of the three different bonds. This means that CF4 has the least ionic character while CBr4 has the greatest ionic character. CBr4 has the most unequal sharing of electrons while CF4 has the least unequal sharing of electrons. I believe that the C--Br bonds could be the strongest because the electrons are attracted strongly because of the higher difference in electronegativity.

[Anastasia Yulo 1C]

To elaborate on the statement "note that electronegativity and polarity arguments would predict the C--F bond to be the weakest", because Fluorine is highly electronegative, then the bond is weak because F is strongly attracting the electron which belong to Carbon. Thus it would be easier for their bond to break given that the electrons are not being equally shared with carbon. Such molecules would likely dissasociate in a solution like water.

[Andre Fabian 1F]

Hi there!

Another way of thinking of it is how ionic bonds aren't really 'bonds.' The ions are attached together in a lattice connected by their charges, with electrons flowing throughout them. As such, it can be said that bonds with a higher difference in electronegativity can be classified as weaker, with higher IONIC character, and bonds with a lower difference in electronegativity can be classified as stronger, with higher COVALENT character.


Hope this helps!