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# BF3<--NH3 shape question

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1. Hi,

The question I’m working on is…

i) use electron pair repulsion theory to deduce the shape of BF3<---NH3
ii) suggest the shape of the molecule if B is the central atom
iii) suggest the shape of the molecule if N is the central atom

On an older post I was looking at for the same question they concluded that BF3 was trigonal planar but I don't understand how BF3 is trigonal planar, surely it has 4 groups of electrons around it, one of which being the lone pair which is a dative bond from the nitrogen?

Wouldn't this mean it's tetrahedral because ithas 4 groups and then because one of the groups is a lone pair the moleculewould be non-linear or pyramidal with a bond angle of 107 degrees?

Thanks in advance for any help,
Blake
2. (Original post by Blake Jones)
Hi,

The question I’m working on is…

i) use electron pair repulsion theory to deduce the shape of BF3<---NH3
ii) suggest the shape of the molecule if B is the central atom
iii) suggest the shape of the molecule if N is the central atom

On an older post I was looking at for the same question they concluded that BF3 was trigonal planar but I don't understand how BF3 is trigonal planar, surely it has 4 groups of electrons around it, one of which being the lone pair which is a dative bond from the nitrogen?

Wouldn't this mean it's tetrahedral because ithas 4 groups and then because one of the groups is a lone pair the moleculewould be non-linear or pyramidal with a bond angle of 107 degrees?

Thanks in advance for any help,
Blake
There is a shared pair of electrons between the N and B so it'll be more like this shape:

So yeah, tetrahedral at both the B and the N.
3. (Original post by alow)
There is a shared pair of electrons between the N and B so it'll be more like this shape:

So yeah, tetrahedral at both the B and the N.
Thanks!

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