AP Chemistry 2014-2015 CH 9 COVALENT BONDING ORBITALS
The localized electron model (from Chapter 8) views a molecule as a collection of atoms bound together by sharing electrons between their atomic orbitals. For example, methane (CH 4 ) consists of one carbon atom bonded to four hydrogen atoms. HYBRIDIZATION AND THE LOCALIZED ELECTRON MODEL
According to the orbital diagram for carbon, there are four valence electrons—two in the 2s subshell, and two in the 2p subshell. One of the 2s electrons can get “promoted” to the 2p subshell. This move allows carbon to form four bonds, one to each hydrogen. However—this would mean that the four C-H bonds are not identical. Experimental observations show that the four C-H are identical, so this model does not correctly explain every aspect of bonding.
We can modify it, though, so that carbon’s 2s and three 2p orbitals “hybridize” to form four identical sp 3 orbitals.
OVERVIEW OF HYBRID ORBITALS Type of HybridizationOrbital CompositionNumber of Electron Domains Common Molecular Geometries sp 1 s 1 p 2Linear sp 2 1 s 2 p 3 Trigonal planar Bent sp 3 1 s 3 p 4 Tetrahedral Trigonal pyramidal Bent dsp 3 (also sp 3 d) 1 s 3 p 1 d 5 Trigonal bipyramidal See-saw T-shaped Linear d 2 sp 3 (also sp 3 d 2 ) 1 s 3 p 2 d 6 Octahedral Square pyramidal Square planar T-shaped Linear
Hybridization of one s orbital and one p orbital Two electron domains Usually occurs when an atom either a) forms double bonds to two different atoms (ex. CO 2 ) or b) forms a single bond to one atom and a triple bond to another atom (ex. HCN). One exception to this is beryllium hydride, BeH 2. Ex. CO 2, HCN, C 2 H 2, N 2, BeH 2 SP HYBRIDIZATION
Hybridization of one s orbital and two p orbitals Three electron domains Usually occurs when an atom forms single bonds to two atoms, and a double bond to a third atom (ex. CH 2 O). One exception to this is boron trifluoride, where boron forms single bonds with three atoms (no double bonds). Ex. C 2 H 4, CH 2 O, BF 3 SP 2 HYBRIDIZATION