Dipole Moment Vector

[MedPR]

Sorry, spamming the forum today! So PCl3 is polar because of the lone pair on the phosphorous (just pretend the oxygen in the picture is a lone pair, it shouldn't change the outcome). So I understand that the net dipole is pointing in the direction of the lone pair - up, in this case.

However, why wouldn't the dipole on SO3 2- be pointing toward the lone pair on sulfur? Don't PCl3 and SO3 have the same shape and the same relative eletronegativities (substituents and central atom)?

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[milski]

The shape is the same. The electronegativity of the central atom should not matter. O is more electronegative than Cl, so the resulting vector of the three O atoms is larger than the same for the three Cl-ines. It's also larger than what you get from the lone pair, so you end up with the resultant pointed down instead of up. It's probably not much of a difference but it seems plausible.

For reference: EN of O is 3.44, of Cl 3.16.

 

[chiddler]

The shape is the same. The electronegativity of the central atom should not matter. O is more electronegative than Cl, so the resulting vector of the three O atoms is larger than the same for the three Cl-ines. It's also larger than what you get from the lone pair, so you end up with the resultant pointed down instead of up. It's probably not much of a difference but it seems plausible.

For reference: EN of O is 3.44, of Cl 3.16.

this is something that must be experimentally determined, right?

 

[milski]

this is something that must be experimentally determined, right?

You could probably calculate it. But you'd need the exact angles and whatever adjustments need to be made to the electronegativity based on which pairs of atoms interact. I imagine that's one of the things people do in pchem?

Realistically, it's probably determined experimentally first and then he math is fudged to match the results. 😎

 

[MedPR]

Ok so PCl3 would have a net dipole moment away from the lone pair? Or toward the lone pair?