Trigonal planar molecular geometry

In chemistry, trigonal planar is a molecular geometry model with one atom at the center and three atoms at the corners of an equilateral triangle, called peripheral atoms, all in one plane.^[1] In an ideal trigonal planar species, all three ligands are identical and all bond angles are 120°. Such species belong to the point group D_3h. Molecules where the three ligands are not identical, such as H₂CO, deviate from this idealized geometry. Examples of molecules with trigonal planar geometry include boron trifluoride (BF₃), formaldehyde (H₂CO), phosgene (COCl₂), and sulfur trioxide (SO₃). Some ions with trigonal planar geometry include nitrate (NO⁻
₃), carbonate (CO²⁻
₃), and guanidinium (C(NH
₂)⁺
₃). In organic chemistry, planar, three-connected carbon centers that are trigonal planar are often described as having sp² hybridization.^[2][3]

Trigonal planar molecular geometry
Examples	SO3
Point group	D3h
Coordination number	3
Bond angle(s)	120°
μ (Polarity)	0

Structure of boron trifluoride, an example of a molecule with trigonal planar geometry.

Nitrogen inversion is the distortion of pyramidal amines through a transition state that is trigonal planar.

Pyramidalization is a distortion of this molecular shape towards a tetrahedral molecular geometry. One way to observe this distortion is in pyramidal alkenes.^[1]

See also

• AXE method
• Molecular geometry
• VSEPR theory