C sp2-hybridized

Cj spi hybridization (4 electron groups) C2 sp2 hybridization (3 electron groups) C sp2 hybridization (4 electron groups)... 

All C-H bonds are of the sp3 type, with tetrahedral H-C-H angles. The bent bonds trace out the density along sp3 orbitals that overlap at an angle, above and below the plane of the nuclear framework. The second possibility assumes the direct overlap of C(sp2) hybrid orbitals. The trigonal array of three sp2 orbitals lies in a plane. The proposed pattern of overlap between two sets of sp2 orbitals accords well with the observed geometry of the ethylene molecule ... 

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