Texas A&M University (TAMU) CHEM 222 Elements of Organic and Biological Chemistry Exam 1 Practice

Four electron domains around the central atom form a tetrahedral arrangement of electron pairs. But here three of those domains are lone pairs, leaving only one bonding pair to define the molecule. The lone pairs occupy three of the tetrahedron’s positions, so the single bond points along the remaining direction, giving a linear arrangement of the atoms. In other words, the molecular geometry is linear because there is only one bond to the outside world, even though the electron-pair geometry is tetrahedral. The other geometries don’t fit: tetrahedral requires four bonds, trigonal planar requires three bonds with no lone pairs, and bent requires two bonds with one or more lone pairs.