Question

How can you use the VSEPR theory?

Answer 1

As we know that the Valence Shell Electron Pair Repulsion theory is a simple method for predicting the shape of covalent molecules and polyatomic ions on the basis of arrangement of molecules.

Complete step-by-step answer:
As we know that a Lewis structure only helps us in identifying the number and types of bonds present between the atoms because they are limited to two dimensions only. To predict their three-dimensional structures and shape we come across the VSEPR theory which is based on the concept that atoms contain electrons around which help in detection of the molecule’s geometry.

VSEPR theory also helps in determining the shape of nearly all the compounds possessing a central atom and thus each shape is named specifically. For instance: the molecule containing a straight chain in their structure with only two number of electrons are normally called linear in shape, similarly the three electrons possessing molecules with no lone pair of electrons is called trigonal planar geometry and if one lone pair is present then the geometry changes to Bent shaped.

We can use VSEPR theory in predicting the shape of a molecule by following some step which include that:
-The total number of electron pairs present around the central atoms which should be the least electronegative atom is given as the sum of half of the valence electron of the central atom and number of atoms linked by single bonds to that central atom.
-The number of bond pairs should be counted as the total number of atoms linked by single bonds with the central atom.
-Lastly, the number of lone pairs of electrons should be counted which is obtained by the difference of total number of electrons and number of shared pairs of electrons. Electron pair numbers are responsible for describing the shape of the molecules such as if the electron pair number is $2$ then the shape is linear like in molecule $BeC{l_2}$.

Note: Remember that VSEPR theory help in describing the shape of a molecule and a molecule with only two atoms is linear, with three atoms is trigonal planar, with four atoms it is tetrahedral, with five atoms it is trigonal bipyramidal, six is for octahedral and seven for pentagonal bipyramidal shape of a molecule.