The difference between the bond enthalpy of HF and F2

Question

I know that the bond enthalpies of F2 is lower, because of the strong replusion
between F2.
But why the graph of bond enthalpies of Hydrogen halide which do not have a sharp drop in hydrogen fluoride ? the hydrogen also contain high charge density like F2

Answer 1

The bond enthalpy of F‑F bond is lower than expected. This is because of the anomalously strong repulsion between the unshared pairs of electrons as F atoms are very small. Note that the repulsion is between the unshared pairs of electrons on one F atom to the unshared pairs of electrons on another F atom.

In HF, there is no such anomalously strong repulsion between H and F atoms, because H atom does not have unshared pair of electrons.



2007-03-20 11:34:27 補充：
Charge density is a quantity to describe the distribution of charge on an ion (esp. a cation).Charge density = (Charge carried by the ion) / (Ionic volume)Charge density is NOT applied to atoms (e.g. H atom) or molecules (e.g. F2 molecule).