SDSU Chemistry Placement Practice Test

An sp² hybridized orbital adopts a trigonal planar shape. This occurs because in sp² hybridization, one s orbital and two p orbitals combine to form three equivalent hybrid orbitals. These three sp² hybrid orbitals are arranged in a plane around the central atom, with angles of approximately 120 degrees between them.

The trigonal planar geometry minimizes electron-pair repulsion according to VSEPR (Valence Shell Electron Pair Repulsion) theory, which states that electron pairs will position themselves as far apart as possible. As a result, the hybrid orbitals are oriented symmetrically around the central atom, leading to the characteristic planar structure.

This geometry is observed in molecules such as boron trifluoride (BF₃) and ethylene (C₂H₄), where the central atom is bonded to three other atoms with no lone pairs influencing the geometry. The distinction between this and other shapes like linear, T-shaped, or tetrahedral stems from the number of regions of electron density and the specific hybridization involved in each case.