bond enthalpies of diatomic molecules

[QUEP 2F]

During lecture, Dr. Lavelle said that bond enthalpies for diatomic molecules are accurate, while all other bond enthalpies are averages and are therefore not as accurate. What is the particular reason for the bond enthalpies of diatomic molecules being accurate, as opposed to other bond enthalpies?

[Rena Wu 3E]

Hi, Dr. Lavelle also mentioned in Friday's lecture that since diatomic molecules only have that one bond, their bond enthalpies are more accurate. On the other hand, more complex molecules have multiple bonds, meaning the bond enthalpies for any specific bond will vary depending on other conditions/surrounding atoms. This explains why these bond enthalpies are averages from different molecules with the same two atoms bonded together. Hope this helps!

[Nataly Antonova 1B]

I believe that bond enthalpies were first determined based on diatomic molecules. Thus, they are exact numbers derived experimentally. For other molecules, approximations from those previous findings were used, this is why there is a possibility of them not being entirely accurate (due to differences in electronegativities in neighboring atoms, etc.)
Hope it helps!

[Tania Peymany 1A]

This is because diatomic molecules are molecules such as H2 or O2, meaning both atoms in the molecule are the same, leading to accurate bond enthalpies. However, other bond enthalpies are between different atoms, so it cannot be as accurate and can only be an average.

[Manya Bajaj 3H]

Another way to understand this idea is that bond enthalpies of bonds which contain more than one type of atom (for e.g. C-H) can exist in multiple compounds which means the energy required to break the bond in each compound may vary slightly depending on the other neighboring atoms as well. Therefore, the bond enthalpy value given in the table for such a bond will be averaged over various compounds and hence is not as accurate. On the other hand, diatomic molecules like H2 or Br2 contain only one type of atom and hence the bond enthalpy can be found accurately for that molecule itself.

[Neeti Indiresan 3I]

I think that for diatomic molecules, the bond enthalpies given are based on what was measured specifically for that bond. On the other hand, in a molecule with many atoms, one bond is not unique to that molecule, but may have slightly varying enthalpies depending on its surroundings in different molecules. For those, we take the average, so it isn't as accurate.