[alishehzad]

Hello...

I have a small conceptual problem. As far as i know, hybridization occurs when electrons prefer to live in different orbitals with same spin rather than same orbitals with different spin.

As far as hybridization in Carbon atom is concerned, it takes place because there are 2 electrons in 2S subshell . and 2 in 2P subshell i.e. Px = 1 , Py = 1 , Pz = 0  

That is why one of the two electrons in 2S shifts to Pz and SP3 hybridization takes place.


However , the problem is with ammonia(NH3). The electronic configuration is 1 S2 , 2 S2 , 2 P3. i.e. Px = 1, Py = 1 , Pz = 1. There is no reason why the 2 S2 shuould over lap with 2P3 and form SP3 orbitals. BUT STILL THEY DO ... and form one lone pair and 3 Half filled bond pairs. (Which afterwards form covalent bonds with Hydrogen atoms)

My question is that why do the 2S2 electrons have to form SP3 orbitals with the 2P3 electrons, when they still remain the same i.e. 2P electrons in different orbitals with same spin and 2S electrons as a lone pair.

[Mitch]

There is no reason why the 2 S2 shuould over lap with 2P3 and form SP3 orbitals. BUT STILL THEY DO ...

Have you looked at the energies of the s2 and 2p in Nitrogen? They are quite close together and do form sp3 hybrid orbitals regularly.

[Winga]

If you familiar with the shape of sp3 orbital, one side of the lobe is bigger which is used to overlap with H 1s orbital that means more e- density between the nuclei (N and H). Therefore, stronger N-H bonds can be formed using sp3 orbitals.

[Winga]

There is one more thing which using sp3 orbitals to form bonds is better than that of using three 2p orbitals. It is about the direction (geometry).