Question

What general principles determine the molecular structure (shape) of a molecule?

Short answer

The molecular structure of a molecule is determined by the Valence Shell Electron Pair Repulsion (VSEPR) theory, which states that electron pairs will arrange themselves in such a way as to minimize repulsion between them. Factors influencing molecular shape include electron domains (bonding and non-bonding), electron domain geometry, and the presence of lone pairs. The molecular shape is determined based on the positions of the bonding electron pairs after considering the central atom, number of electron domains, and the influence of lone pairs.

Step-by-step solution

Introducing the Valence Shell Electron Pair Repulsion (VSEPR) Theory

The Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the molecular geometry of individual molecules based on the number of electron pairs in the valence shell of the central atom. This theory states that electron pairs will arrange themselves in such a way as to minimize repulsion between them.

Understanding Electron Domains

Electron domains are regions in which electrons are most likely to be found. In the context of VSEPR theory, there are two types of electron domains: bonding domains and non-bonding domains (lone pairs). Bonding domains are electron pairs shared between two atoms, forming a covalent bond, and non-bonding domains are lone pairs of electrons that belong to the central atom and are not involved in bonding.

Determining the Electron Domain Geometry

Based on the number of electron domains present around the central atom, VSEPR theory assigns electron domain geometries. A simple table of electron domains and their geometries is as follows: 1. 2 electron domains -> Linear geometry 2. 3 electron domains -> Trigonal planar geometry 3. 4 electron domains -> Tetrahedral geometry 4. 5 electron domains -> Trigonal bipyramidal geometry 5. 6 electron domains -> Octahedral geometry

Considering the Effects of Lone Pairs on Molecular Shape

The presence of lone pairs can alter the molecular shape as they exert greater repulsive forces on bonding pairs compared to other bonding pairs. When assigning molecular shapes, the positions of the lone pairs are considered. The molecular shape is then determined by the positions of the bonding pairs of electrons. For example, if a central atom has four electron domains with one lone pair and three bonding pairs, the molecular shape would be trigonal pyramidal rather than tetrahedral.

Applying the VSEPR Theory

To apply the VSEPR theory to determine the molecular structure, perform the following steps: 1. Identify the central atom of the molecule. 2. Count the number of electron domains around the central atom (both bonding and non-bonding). 3. Assign the electron domain geometry based on the number of electron domains. 4. Take into account the influence of lone pairs on the molecular shape. 5. Determine the molecular shape based on the positions of the bonding electron pairs. In summary, the molecular structure of a molecule is determined by the valence shell electron pairs' arrangement around the central atom, according to the Valence Shell Electron Pair Repulsion (VSEPR) theory. Factors such as electron domains, electron domain geometry, and the presence of lone pairs influence the molecular shape.