Arrange the following covalent bonds in increasing order of bond strength: C-F, C-Br, C-CL, C-I. GIVE REASONS?

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  • Iggy has the order correct be the reason is somewhat different
    C-F 485 > C-Cl 327> C-Br >285>C-I >213
    http://www.wiredchemist.com/chemistry/da…
    Bond strength can be related to the overlap integral E(bond) α ∫φ(C)×φ(X)dτ where φ(C) is the Schrödinger Wave Function AO for C (for you an sp^3 σ AO will suffice); φ(X) is the np AO on the halide. Google Overlap Integral. So yes there is good overlap for the C-F bond because the 2p AO of F is small. The overlap decreases 3p(Cl)<4p(Br)<5p(I). These functions are more diffuse. I also think that much of the heavier element np AO is beneath the core electrons that also prevents good overlap but I haven’t seen this mentioned in texts.

  • I’d arrange these from strongest to weakest:
    C-F > C-Cl > C-Br > C-I

    The reasons. Firstly I believe the C-F will be strongest because 1) the size of the F is much smaller 2) The electronegativity difference makes the bonding more polar, with some added attraction between the two atoms due to charge

    This explains the order I’ve placed the other bond strengths also.

    Hopefully this is of some help.

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