Molecules

Molecules

Molecules align themselves as three-dimensional structures that determine their physical and chemical properties. The molecule valence electron pairs govern the orientation. The valence shell electron pair repulsion (VSEPR) theory states attempts to explain molecular structure through its postulate that; valence electron pairs repel each other as much as possible. The theory also makes the following deductions that determine the geometry of various molecules.

1. Electron pairs around the central atom in a molecule are far away from one another.
2. Lone pairs on the central atom have an equal impact on the molecule’s geometry as if they constituted a bonding pair.
3. Lone pairs repel each other more strongly than a lone and a shared pair.

Following the above postulates, it is possible to determine the geometry of a molecule so long as we know the compound’s chemical formula. For instance, the molecular geometry for the following compounds can be explained using the VSEPR theory.

1. CO₂

The central atom, in this case, is carbon bonded to two oxygen atoms. According to the VSEPR theory, the carbon atoms’ electron pairs will be as far as possible, thus forming a linear structure, as shown below.

O=C=O

1. H₂O

In the molecule of water, the central atom is oxygen bonded to two oxygen molecules. Unlike in CO2, the central atom has two pairs of free electrons that repel the hydrogen-oxygen bonded pairs, thus altering the structure as shown.

The above structures were confirmed using a computer-simulated program. Other molecular structures examined were CH₄, NH₃, and PCl₅. CH₄ demonstrated a tetrahedral structure, while NH₃ showed a trigonal pyramidal structure. PCl₅ demonstrated a trigonal bipyramidal. All the structures conform to the VSEPR theory.