Question

What can the electronegativity difference between the atoms in a molecule of HCI can be used to determine?

Answer 1

See below

Explanation:

The `DeltaEN` tells us the type of bond about the species, and as such it also tells us how the electron are shared about the species.

If the `DeltaEN` is high, (the difference is large) this indicates that one of the constituent species has a relatively high electronegativity value and the other species has a relatively low electronegativity value.
One species is always going to be at least slightly more electronegative than the other unless they are the same species.

In our case, for determining the `DeltaEN` about the `"HCl"` species:

For the `"H-Cl"` bond:
`3.16 - 2.20 = DeltaEN`
`0.96 = DeltaEN`

And when using the Pauling scale of electronegativity values to find the electronegativity difference, usually, if:

`0 < DeltaEN < 0.5` the bond should be covalent
`0.5 < DeltaEN < 2.1` the bond should be polar covalent
`2.1 < DeltaEN` the bond should be ionic

So using the Pauling scale and subtracting the electronegativity values of `H` and `Cl` to find the `DeltaEN`...

tells us that the `"H-Cl"` bond should be polar covalent .

Since we know that the bond is polar covalent, this tells us how the electron are shared about the species. Try to imagine how the electron are interacting about the species:

Consider the graphic below: