[mps]

Hello,
WRT H-bonding, I'd understood that hydrogen bonds arise between the positive dipole moment of Hydrogens (bonded to F,O,N) and the negative dipole of F, O, or N atoms (bonded to H).  Another source says H-bonds form between the positive H-dipole and the lone electron pairs on the electronegative elements.  In this case, the H-bond is not due to the partial dipole charge from unevenly shared electrons, but from a completely unshared pair of electrons associated with the electronegative element.  It says B(OH)3 can form nine H-bonds: 3 H-bonds involve the positive-dipole H, and 6 H-bonds form between the 6 lone pair of electrons (2 lone pairs per oxygen) and hydrogens of neighboring molecules. 

Is it better to think of H-bonds forming between H and lone electron pairs, or between H and F/O/N dipole arising from unevenly shared electrons of a polar covalent bond?

How do we predict the number of H-bonds a molecule can participate in?  The same source says 3 H-bonds form between an NH3 molecule and the hydrogens of three neighboring NH3 molecules; and that all three hydrogens are pointing toward (ie attracted to) Nitrogen's lone pair of electrons.  Could we have predicted ammonia participates in 3 H-bonds??  How?

Thanks for clarifying.

[AWK]

What about bifurcated hydrogen bonds?