The VSEPR theory is very important in chemistry since it helps in predicting the arrangement of electron pairs around central atoms. Under this theory there is an important chapter named VSEP number which also helps in studying the atoms. If you don’t know about this number then keep reading this article.

Before we will explain to you about this number it’s very important to first understand the meaning of VSEPR theory. So, let’s see in simple words the meaning and applications of VSEPR theory.

What is VSEPR Theory?

The full form of VSEPR is Valence Shell Electron Pair Repulsion. It is commonly used in chemistry in order to predict the geometry of individual molecules from the number of electron pairs that are surrounding the central atom. We all know that atoms bond chemically to transform themselves into a molecule. 

During this process of transformation two forces are used: attraction force which consists between nucleus and electrons and repulsion force which occurs between the electrons.

The repulsion that is created between the valence electrons decides the shape of the atom. The VSEPR theory states that the valence electron pairs surrounding an atom will repel each other. Due to this the atoms will arrange themselves in a manner that helps in reducing this repulsion. This will ultimately reduce the molecule’s energy and its stability will increase which will help in predicting the molecular geometry.

Ronald Nyholm and Ronald Gillespie are the two main founders of VSEPR theory. This is the reason why this theory is also popularly known as the Gillespie-Nyholm theory. The VSEPR theory also tells us that the Pauli exclusion principle which is responsible for the electron-electron repulsion holds a greater importance in determining molecular geometry than electrostatic repulsion.

Terms Used in Studying the Shapes of Molecules

You need to understand the meaning of the terms given below in order to understand the shapes of molecules:

Bond Angle

An angle which is formed between two bonds that are originating from the same atom in a covalent species is termed as bond angle.

Lone Pair

Lone pair is a pair of valence electrons in a covalent bond that are not shared with another atom. Usually they are found in the outermost electron shell of atoms.

Molecular Geometry

Molecular geometry is the 3-D arrangement of the atoms that constitute a molecule.

Electron Pair Geometry

Electron pairs geometry is the 3-D arrangement of electron pairs around the central atom.

What is VSEP Number?

The VSEP is primarily used to describe the shape of the molecule.

How to find VSEP Number?

1. First you need to find the central atom.
2. Then you need to count how many valence electrons of the central atom are there.
3. The third step is to carry out a simple addition of one electron for each bonding atom.
4. Afterwards you need to add or subtract electrons according to the charge they have. This means for negative ions you need to add the number of electrons which is equal to the units of negative charge on the ions to the valence electrons.
5. For positive ions you need to do the opposite i.e. subtract the number of electrons which is equal to the units of positive charge on the ion from the valence electrons.
6. Finally, divide the total which you get above by 2. This will help you to find the total number of electron pairs.
7. The answer you get is your VSEPR number.

Conclusion

We hope that after reading this article you got a better idea about the VSEPR theory and number. Both are extremely important in studying the arrangement and shape of the atoms. Just remember that the VSEPR theory helps in predicting the geometry of individual molecules from the number of electron pairs that are surrounding the central atom. Under this theory the VSEP number is used to describe the shape of the molecule.