The bond angles depend on the number of lone electron pairs. For example, boron trichloride has no lone pairs, a trigonal planar shape and bond angles of 120 degrees. The trioxygen molecule O3 has one lone pair and forms a bent shape with bond angles of 118 degrees. On the other hand, O2 has two lone pairs and a linear shape. Methane, which has no lone pairs, forms a tetrahedron with 109.5-degree bond angles. Ammonia has one lone pair, creating bond angles of 107.5 degrees and a trigonal pyramidal shape. Water, with two lone pairs of electrons, has a bent shape with 104.5-degree bond angles.
The VSEPR theory assumes that each atom in a molecule will achieve a geometry that minimizes the repulsion between electrons in the valence shell of that atom. It is basically a model to predict the geometry of molecules. Mainly VSEPR models look at the bonding and molecular geometry of organic molecules and polyatomic ions.
- The VSEPR model predicts the 3-D shape of molecules and ions but is ineffective in providing any specific information regarding the bond length or the bond itself.
- VSEPR models are based on the concept that electrons around a central atom will configure themselves to minimize repulsion, and that dictates the geometry of the molecule.
- It can predict the shape of nearly all compounds that have a central atom