Table of Contents
What is a Trigonal Pyramidal Arrangement? ;
A trigonal pyramidal arrangement is a molecular geometry in which three atoms or groups of atoms are arranged at the vertices of an equilateral triangle, with the fourth atom or group of atoms at the center.
Trigonal Pyramidal Molecular Geometry
In trigonal pyramidal molecular geometry, the three bonding electron pairs are arranged in a triangular pyramid, with the electron pair at the apex of the pyramid. The unbonded electron pair occupies the lower three corners of the pyramid. This geometry is found in molecules such as ammonia and water.
Trigonal Pyramidal Geometry in Ammonia
The ammonia molecule has a trigonal pyramidal geometry, with the nitrogen atom at the apex of the pyramid. The three hydrogen atoms are located at the base of the pyramid, in the plane of the triangle formed by the nitrogen atom and the two other hydrogen atoms. This geometry is due to the fact that the nitrogen atom has a lone pair of electrons that can form a strong bond with the hydrogen atoms.
Axial (or Apical) and Equatorial Positions
Axial position is the position of an atom or molecule in a crystal that is perpendicular to the crystal axis. Equatorial position is the position of an atom or molecule in a crystal that is parallel to the crystal axis.
Related Geometries with Lone Pairs
There are a few other geometries that have lone pairs. These are the linear geometry, the trigonal bipyramid geometry, and the octahedral geometry.
