Hybridization Question

[h20h]

HI! I have a quick question...we were asked on a quiz to draw the lewis dot structure for AsH3. Then describe the bonding scheme for the molecule in terms of hybridization.

I wrote that since As is in group 5...it has 5 electrons with 3 H bonded to it. In lab we were told to count lone pairs as one, so wouldn't you need 2 lone pairs to get up to 5 electrons? Or do you count the individual electrons individually? That is where I am confused...becuase if you count the lone pair as one group you would need another lone pair to get to 5? She gave us an answer for the hybridization of sp3 where I said sp3d...can you explain please?

Thanks
h20h

 

[dextercioby]

The As has 5 binding electrons, and uses 3 to form covalent bounds with H. The other 2 form a lone pair. The situation is identical with ammonia NH_{3}. The hybridization for ammonia is sp_{3}. The same goes for water H_{2}O, but for the latter, there are 2 lone pairs from the 6 valence electrons of O.