dipole moment and lone pairs

[lamborghiniMD]

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Suppose element B is MORE electronegative than element A:

If they form a compound like this: B--A--B, there would be no net dipole moment,

but what if the compound was like this: B--A:--B (A has 1 lone pair)
and B--:A:--B (A has 2 lone pairs). What would the net dipole moment be then?

 

[shaboobly]

Suppose element B is MORE electronegative than element A:

If they form a compound like this: B--A--B, there would be no net dipole moment,

but what if the compound was like this: B--A:--B (A has 1 lone pair)
and B--:A:--B (A has 2 lone pairs). What would the net dipole moment be then?

treat the dipoles like a vector and add; you need to determine the shape of the molecule first which will tell you the bond angles.

 

[LoLCareerGoals]

Using VSPER model, yes B-A-B is a linear molecule and has zero dipole moment.

B-A:-B is triangular (bent at about 120, but slightly compressed by the pair) and will have some dipole moment, most likely pointing toward a lone pair, since it is doubtful el-neg difference of A&B is strong enough (even summed over 2 vectors) to outweigh a lone pair's negativity.

B-:A:-B is also bent (but at an angle closer to 109 degrees, but less than that because lone pairs will compress the angle). Here too we should have a dipole moment, most likely pointing toward the middle of the 2 lone pairs.

To solve a problem like this more precisely, we do need bond distances, partial charges etc etc, but for a quick general answer ^ should suffice.