Trigonal Pyramid..molecular geometry/inorganic chemistry
Shape: trigonal bipyramidal
Steric Number: 5
Lone Pairs: 0
Polar/NonPolar: NonPolar
Hybridization: sp3d
Examples: PCl5, SbF5
NOTES: This molecule is made up of 5 sp3d hybrid orbitals. Three orbitals are arranged around the equator of the molecule with bond angles of 120o. Two orbitals are arranged along the vertical axis at 90o from the equatorial orbitals. The shape of the orbitals is trigonal bipyramidal. Since there is an atom at the end of each orbital, the shape of the molecule is also trigonal bipyramidal.Ammonia

An example of trigonal pyramid molecular geometry that results from tetrahedral electron pair geometry is NH3. The nitrogen has 5 valence electrons and thus needs 3 more electrons from 3 hydrogen atoms to complete its octet. This then leaves a lone electron pair that is not bonded to any other atom. The three hydrogen atoms and the lone electron pair are as far apart as possible at nearly 109o bond angle. This is tetrahedral electron pair geometry.The lone electron pairs exerts a little extra repulsion on the three bonding hydrogen atoms to create a slight compression to a 107o bond angle.The molecule is trigonal pyramid molecular geometry because the lone electron pair, although still exerting its influence, is invisible when looking at molecular geometry. The molecule is three dimensional as opposed to the boron hydride case which was a flat trigonal planar molecular geometry because it did not have a lone electron pair.