Sulfur tetrafluoride, abbreviated as SF4, has a trigonal bipyramidal electronic geometry. This means that the central sulfur atom is bonded to four fluorine atoms and has one lone pair of electrons.
According to valence shell electron pair repulsion theory, the atoms and the lone pair will move as far apart as possible, which in this case gives a trigonal bipyramidal configuration. This structure consists of a flat plane of two fluorines and a lone pair, much like the structure of a trigonal planar molecule. Above and below the plane (at the top and bottom of the molecule) are two more fluorines. Lone pairs take up more space than atoms; therefore, the lone pair is in the plane because that allows it to be the farthest from other molecules.