Accurate and estimation of bond enthalpy

[Maria Solis Disc 1G]

During class today Dr Lavelle stated that all diatomic molecules bond enthalpies were accurate, and that all other bond enthalpies were averages. I was wondering if someone could explain what a diatomic molecule was. I also vaguely remember Dr. Lavelle stating that C2's bond enthalpy is composed of averages, and was wondering how.

[Riya Shah 4H]

a diatomic molecule is a molecule like N2, O2, HCl, which has only 2 elements.

[Xinyi Zeng 4C]

Diatomic molecules are molecules composed of only two atoms, and the two atoms can be of the same or different chemical elements. The reason that the bond energy of C-C is not as accurate is because there is no such thing as C2, and C-C bond energy is calculated as an average of bond energy of C-C in many different molecules that contain the C-C bond, like CH3CH3, CH3CH2CH3...

[LilyL1C]

There are only 7 diatomic molecules, and they are H2, N2, F2, O2, I2, Cl2, and Br2.
And the bond energies of any other bond is an average because since it cannot be measured like those of diatomic molecules are. For example, to achieve this average for C-C, you take the energies of every single C-C bond that exists in every molecule and average them.