About the Orbital Dipole Moment

[S Aditya]

I was going through the chapter Chemical Bonding in one of the books and found something about orbital dipole due to lone pairs.

In each diagram the orbital dipole due to lone pair was directed from the central atom to the end of the hybridized orbital (lone pair).

Why is that so?

 

[DrClaude]

Conventionally, in chemistry, the dipole moment is indicated as pointing from δ⁺ to δ^-. This is in contrast with the convention in physics where the dipole moment points towards the positive charges.

The presence of the lone pair contributes to the δ^-. In addition, the fact that there is a lone pair is an indication that the atom on which it resides is more electronegative, which explains the presence of the arrows pointing from H to N n the first figure. All this makes the dipole moment point towards the lone pair.

 

[S Aditya]

Conventionally, in chemistry, the dipole moment is indicated as pointing from δ⁺ to δ^-. This is in contrast with the convention in physics where the dipole moment points towards the positive charges.

The presence of the lone pair contributes to the δ^-. In addition, the fact that there is a lone pair is an indication that the atom on which it resides is more electronegative, which explains the presence of the arrows pointing from H to N n the first figure. All this makes the dipole moment point towards the lone pair.

Sir, my argument is why is the dipole moment of the lone pair (and the lone pair alone) poining upwards (in this case) from the central atom (Nitrogen) to the extremity of the hybridized lone pair orbital?

 

[DrDu]

Conventionally, in chemistry, the dipole moment is indicated as pointing from δ⁺ to δ^-. This is in contrast with the convention in physics where the dipole moment points towards the positive charges.

I never heard of such a convention. Rather, I think that the arrows denote the polarity of the bond, and not the dipole moment. But admittedly, for a non-bonding pair there is n't much sense in speaking of the polarity.

 

[DrClaude]

The way I learned it is as on this page: http://people.uwplatt.edu/~sundin/114/l114-31.htm

You draw a cross on the plus side, then the arrow towards negative.

 

[DrDu]

Hm, maybe this is country specific?