The thumb rule reveals: facilitating the transition from electron geometry to molecular geometry and vice versa
Gyan M. Narayan
Both 1st and 2nd semester students of General Chemistry are introduced to the concepts of electron and molecular geometry as part of a chapter concerning “Chemical Bonding” (sections following Valence Shell Electron Pair Repulsion Theory). Often, instructors note that students encounter difficulties discriminating between the electron geometry and the molecular geometry of a molecule which is dependent on the presence of lone pairs on the central atom. We propose a “thumb rule” that is designed to “reveal” any difference between the two said geometries and thereby facilitates the transition from electron to molecular geometry and vice versa. The use of this technique is additionally advantageous since it is simple to apply and does not require any materials (and is therefore free of charge). Importantly, it is a fun exercise that facilitates learning.