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Does electronegatvity affect bond energy?

I just wanted to know if bond energy takes into account electronegativity? Because for ionic compounds we use theoretical values assuming that the compounds are "purely ionic," so is it the same for covalent bonds (ie. does bond energy assume that the compounds are ''purely ionic"?)? Thanks :smile:
Bond enthalpies are typically measured values, so they take into account the effect of electronegativity by default - as would any modern theoretical model to deduce them would :yep:
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krishthakrar
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Original post by EierVonSatan
Bond enthalpies are typically measured values, so they take into account the effect of electronegativity by default - as would any modern theoretical model to deduce them would :yep:


But then why is it that when calculating values for ionic compounds like lattice energies, we use theoretical values, such as ionisation energies and electron affinity, which don't take into account electronegativity?
(edited 10 years ago)
Original post by krishthakrar
But then why is it that when calculating values for ionic compounds like lattice energies, we use theoretical values, such as ionisation energies and electron affinity, which don't take into account electronegativity?


''We'' don't. The theoretical values have been obtained from a simple model that only takes into account a pure ionic framework, which is used for ease. We then compare the calculated values to experimental ones and notice a discrepancy in some cases - and the simplistic model is ill suited to the task in certain cases. If the two values don't match up, we know that there is a significant degree of covalency involved.
(edited 10 years ago)
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krishthakrar
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Original post by EierVonSatan
''We'' don't. The theoretical values have been obtained from a simple model that only takes into account a pure ionic framework, which is used for ease. We then compare the calculated values to experimental ones and notice a discrepancy in some cases - and the simplistic model is ill suited to the task in certain cases. If the two values don't match up, we know that there is a significant degree of covalency involved.


ok that makes sense, thanks for your help :smile:
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krishthakrar
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Sorry one more question, why are there no values for bond energies of ionic bondd like na-cl or k-cl available. Surely they are just as useful as bond energies of covalent bonds?

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Original post by krishthakrar
Sorry one more question, why are there no values for bond energies of ionic bondd like na-cl or k-cl available. Surely they are just as useful as bond energies of covalent bonds?


Lattice enthalpy is the ionic equivalent of covalent bond energy. In covalently bonded molecules it's fairly easy to define a single bond - but this isn't possible in an ionic lattice where every positive ion is being attracted to every negative ion from all directions (and vice versa). So we can't isolate a single bond between one anion and one cation - so we just worry about the attractive energy of a given amount.
Original post by krishthakrar
But then why is it that when calculating values for ionic compounds like lattice energies, we use theoretical values, such as ionisation energies and electron affinity, which don't take into account electronegativity?


The electronegativity is not the answer to everything. Think of it as more like atomic radii, a result of more fundamental factors. Infact electronegativity is actually often defined using the other two factors you just stated. There are many other ways of defining electronegativity and it's not an exact value in the same way IE is... i.e. you can't measure it directly.

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