Advanced Placement (AP) Chemistry Practice Exam

Trigonal planar geometry involves which type of hybridization?

1. sp hybridization

2. sp2 hybridization

3. sp3 hybridization

4. sp4 hybridization

The correct answer is: sp2 hybridization

Trigonal planar geometry is characterized by a central atom surrounded by three regions of electron density, which can be in the form of bonds or lone pairs. This arrangement leads to bond angles of approximately 120 degrees, which is typical for molecules that exhibit this geometry. The hybridization that corresponds to a trigonal planar molecular shape is sp2 hybridization. In sp2 hybridization, one s orbital and two p orbitals from the central atom mix to form three equivalent sp2 hybrid orbitals. These hybrid orbitals lie in a plane and are oriented 120 degrees apart, allowing for the formation of three sigma bonds with surrounding atoms, while any remaining unhybridized p orbital is oriented perpendicular to that plane. This geometry is commonly seen in molecules such as boron trifluoride (BF3) and ethylene (C2H4). Understanding how hybridization relates to molecular geometry is crucial in predicting the shapes of molecules through the Valence Shell Electron Pair Repulsion (VSEPR) theory, which highlights the importance of electron pair repulsion in defining molecular structure. The other hybridization types, such as sp, sp3, and the nonexistent sp4, have different arrangements and bond angles that do not align with the trigonal planar