[student8607]

I'm trying to do homework that was never explained in class and that our book only explains and doesn't give any examples for. 

What hybridization would you expect for:
BH4-

I know how to write the dot structures and the configurations, but after that I have no idea what to do. I understand that its combining orbitals or something, but....

[Astrokel]

hey student8607,

you would like to read this first: http://www.chemicalforums.com/index.php?topic=28447.msg107830#msg107830

[student8607]

wow this is why i love this forum
you guys say in 2 sentences what my book takes 8 pages to equivocate

just to double check:
BH4^- --> sp3 because 4 bonds & 0 lone pairs
HCO2^- --> sp2 because 3 bonds & 0 lone pairs
CH3^+ --> sp3 because 3 bonds & 1 lone pair
CH3^- --> sp3 because 3 bonds and 1 lone pair

[Astrokel]

CH3^+ --> sp3 because 3 bonds & 1 lone pair

I think you make a slight careless mistake in this. The rest are correct, good try.

[student8607]

I was a little confused with that one, even with doing the dot structure.

1. 4valence of carbon + 3valence for the hydrogens - 1valence since it is a + = 6 total valence available
2. need 6valence for the hydogens and 8valence for the carbon= 14 total needed
3. 14-6=8 need bonds
4. 8/2 = 4 bonds
but how can I form 4 bonds when each H will only have a single bond?

[Astrokel]

I don't quite understand your working, CH₃⁺ should be sp² hybdridised as carbon will form 3 single bond with each hydrogen atom also there is 0 lone pair due to the positive charge.

[student8607]

But then Carbon wont have an octet?

[Borek]

It won't.

[Astrokel]

But then Carbon wont have an octet?

It won't as Borek mentioned, but it is not really a matter of stable electronic configuration or not.

[student8607]

OK. Understand now. Thanks guys