hybridization

Refer to the structure given :

圖片參考：http://hk.geocities.com/hoocch2ch2cooh/diagrams/caffeine.jpg


C atoms in red : sp3 hybridized
The four sp3 orbitals are used to make four σ bonds (single bonds).

C atoms in blue : sp2 hybridized
The three sp2 orbitals are used to make three σ bonds, and the unhybridized 2pz orbital are used to make one π bond (a double bond contains a σ bond and a π bond).

N atoms in red : sp3 hybridized
One of the four sp3 orbitals is corresponding to a lone pair, and the other three sp3 orbitals are used to make three σ bonds.

N atoms in blue : sp2 hybridized
One of the three sp2 orbitals is corresponding to a lone pair, the other two sp2 orbitals are used to make two σ bond, and the unhybridized 2pz orbital are used to make one π bond.

O atoms in black : not hybridized
2s and 2px orbitals are corresponding to two lone pairs, 2py is used to make a σ bond, and 2pz is used to make a π bond.
(Terminal atoms are always not hybridized.)

i want to ask Uncle michael.Why red N is not sp2 ?There are only three σ bonds.Thanks