Second row p-block atoms have the four valence shell atomic orbitals shown. However, use of pure 2s and 2p orbitals for bonding at boron (B), carbon (C) and nitrogen (N) is not consistent with experimental facts.
In BF3 and CH4 all bonds are equivalent and symmetrically distributed about the central atom.
The B-F bond angle in BF3 is 120°; the C-H bond angle in CH4 is 109.5°.
The bond angle at carbon depends on the number of atoms bonded to the carbon. For HC≡CH it is 180°
The B-F bond angle in BF3 is 120°; the C-H bond angle in CH4 is 109.5°.
The bond angle at carbon depends on the number of atoms bonded to the carbon. For HC≡CH it is 180°
 2s |  2p |  2p |  2p |
Linear combination of atomic orbitals to give hybrid orbitals is possible for orbitals of similar energy (such as the 2s and 2p orbitals for B, C, and N).
In all cases the number of hybrid orbitals resulting is equal to the number of atomic orbitals combined. The shape and orientation of the hybrid orbitals depends on the number and types of orbitals that are combined.
Hybrid orbitals overlap with other orbitals in forming σ bonds.
The different types of hybrid orbitals have different orientations about the nucleus of the hybridized atom corresponding to the different bond angles described above.
In all cases the number of hybrid orbitals resulting is equal to the number of atomic orbitals combined. The shape and orientation of the hybrid orbitals depends on the number and types of orbitals that are combined.
As shown in the diagram, different hybrid sets result from hybridizing the 2s orbital with different numbers of 2p-orbitals. Like the unhybridized atom, hybridized atoms have four orbitals available for bonding.
Hybrid orbitals overlap with other orbitals in forming σ bonds.
The different types of hybrid orbitals have different orientations about the nucleus of the hybridized atom corresponding to the different bond angles described above.
- sp3 hybrid orbitals point to the corners of a tetrahedron (109° angle between them)
- sp2 atom hybrid orbitals point to the corners of a equilateral triangle (120° angle)
- sp hybrid orbitals point to the ends of a line (180° angle between them).
 sp3 | sp3 | sp3 | sp3 |
 sp2 | sp2 | sp2 | 2p |
 sp | sp | 2p | 2p |