NABH4 geometry

[SaintJude]

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It's electron geometry: trigonal bipyramidal

Molecular geometry is: seesaw

👍 ?

 

[Dasypus]

Sorry, it really is just as tetrahedral as it looks in the picture.

BH3 is neutral. To add a hydrogen, you need two electrons to form a bond. Hydrogen natively has one. The other electron completes the bond and puts the negative charge on the molecule.

 

[chiddler]

it doesn't have lone pairs. both are tetrahedral.

 

[gettheleadout]

Technically this is just BH4- geometry... 😛

But really, weird case with that formal charge if you haven't seen it before.

 

[MedPR]

I agree with tetrahedral.

 

[SaCkO]

mmm.. not sure

 

[SoulinNeed]

Wait, are we talking about NaBH4 or just BH4, or is there no difference due to it being ionic (it is, right?).

BH4- looks tetrahedral to me.

 

[gettheleadout]

The answer is definitely tetrahedral, for both electron group and molecular geometries. Were there a lone pair on the boron, the formal charge would be 3-, whereas a formal charge of 1- indicates one extra valence electron, and this is from the one electron in the fourth B-H bond which contributes to boron's valence (while the other contributes to the hydrogen's valence.)

Looking at the structure of a single formula unit of NaBH4 is more difficult; Lewis structures do not represent ionic bonds (like that between Na+ and BH4- using bond lines, and as a compound NaBH4 has several crystalline polymorphs. The question is definitely referring to the structure of the tetrahydroborate ion itself (BH4-).

 

[MedPR]

Yea, I don't think we can define a shape for NaBH4 since the VSEPR shapes apply only to covalent bonds.