AX3E2

AX3E2 is a designation used in Valence Shell Electron Pair Repulsion (VSEPR) theory to describe a molecule or ion where a central atom A is bonded to three substituents X and contains two nonbonding electron pairs E. In this arrangement, the electron-domain geometry is trigonal bipyramidal, while the resulting molecular geometry is T-shaped.

In AX3E2 species, the two lone pairs adopt equatorial positions in the trigonal bipyramidal arrangement to minimize repulsion. This leaves three X ligands occupying two axial positions and one equatorial position, producing a T-shaped molecular geometry. The axial bonds experience greater repulsion than the equatorial bond, leading to typically longer axial X–A bonds and a shorter equatorial X–A bond. Bond angles are around 87 degrees between the axial and equatorial substituents, with the two axial bonds separated by about 180 degrees.

Common examples of AX3E2 species include chlorine trifluoride (ClF3), bromine trifluoride (BrF3), and iodine trifluoride (IF3). These molecules are often highly polar and can be strong oxidizers. While VSEPR provides a useful framework, real-world structures can show deviations due to differences in ligand size, electronegativity, and other bonding factors, leading to slight distortions from the idealized T-shaped geometry.