Why do BF3 and NH3 bond together to form BF3NH3 if boron only needs 6 valence electrons? If boron is happy with 6, then why would it create a double covalent bond with nitrogen that has a lone pair of electrons?

Question

photon336 · Answer

I think Boron is an exception, it has an empty p orbital that can accept electrons.

photon336 · Answer

Boron is also a strong Lewis acid meaning that it can accept a pair of electrons in what's known as a coordinate covalent bond

photon336 · Answer

The bond happens when both the electrons come from the same atom, in this case nitrogen.

aaronq · Answer

it doesn't create a double bond with nitrogen, it's a single bond. It's all about that empty p orbital though

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anonymous · Answer

Oh so when they bond, nitrogen donates one electron to boron and because now they have opposite charges they are attracted to each other similar to how an ionic bond is formed?

photon336 · Answer

@coltonpalmer an ionic bond is when there's a transfer of electrons, electrostatic attraction; this case is different because it's not an ionic bond but rather a coordinate covalent bond, note "covalent". The issue here is that boron is one of those exceptions, but the best way to think of it is  as a Lewis acid; Lewis base pair where the electrons are coming from the nitrogen. Boron is a bit funny because it's one of those exceptions. A Lewis acid by definition is an atom that can accept a pair of electrons.

photon336 · Answer

But I guess you could think of it that way just remember that it's not ionic.

anonymous · Answer

ok thank you :) @Photon336 @aaronq

aaronq · Answer

The charges are formal charges, not ionic.