What Is the Vsepr Model?

The Vsepr Model is a chemistry model that is used to predict individual molecules shapes, by using steric numbers and the extent of their electron pair electrostatic repulsion. The word VSEPR stands for valence shell electron pair repulsion, and this is at times referred to as Gillespie-Nyholm theory. This theory relies on the idea that a molecule's geometry is primarily determined by its repulsion amidst electron pairs that are associated with a central or primary atom.

History

The Vsepr model was first presented in 1940 at a Bakerian Lecture by Nevil Vincent Sidgwick, a theoretical chemist from England and Herbert Marcus Powell, head of the Chemical Crystallography Laboratory at Oxford University. Sidgwick's and Powell's model was later refined and developed into a detailed theory by Ronald J. Gillespie and Ronald Sydney Nyholm. Both Gillespie, a professor of chemistry at McMaster University and Nyholm, an Australian chemist, did comprehensive work in expending valence shell electron pair repulsion theory.

Function

The function of Vsepr theory is to show that to predict the geometric shapes and lone pair behaviors of molecules, one must consider the total steric numbers of the molecules, as well as the lone pairs of electrons. This is based on the theory that electrons, with a negative valence charge, work together to repel each other.

Significance

Vsepr theory is significant in that it shows that not just the shape of a molecule, but also its physical properties, are determined by the arrangement of an atom. For example, the chemical compounds in a medication are only biologically active when the chemical order is perfectly arranged. If molecules of the chemical compound are not arranged correctly, the medication will not work effectively when used.

Identification

Using Vsepr theory, a molecule's shape can be identified by having or containing a certain set of traits. One of these traits is that a primary atom's valence shell contains electron pairs that repel each other. Another is that these electron pairs will most often occupy positions that will allow for the repulsion to be minimized and the distance that they are separated from each other in to be maximized.

Considerations

There are three different types of repulsion that can take place when dealing with the electrons that are contained in a molecule. These repulsions must not take place for the molecule to stay stable. When the molecule is not stable, the chemical compound of the item can break down. If repulsion must happen, it is hoped that the repulsion of the weakest magnitude will occur; leaving the shape of the molecule as close as possible to what it would have been if the repulsion had not happened in the first place.