If you are a student learning chemistry today, you have probably come across the term “Lewis structure” at least once. For the uninitiated, it may seem like yet another last name of another important chemist. However, the Lewis structure is significant in several aspects of modern chemistry.
A solid understanding of it is going to be critical in helping tackle more complex areas of chemistry. In this article, let us take a close look at the Lewis structure and what purpose it serves.
Who Was Gilbert Lewis?
On October 25, 1875, Gilbert N. Lewis, one of America’s most notable chemists, was born. In 1923, Lewis won the Nobel Prize for discovering covalent bonds and for applying the principles of thermodynamics to chemical reactions. In fact, Lewis contributed significantly to many concepts that we still use today. These include:
- Lewis acids and bases
- Electron pair repulsion theory
- Lewis notation (in the context of thermodynamics)
- Isotope separation
- Lewisite (a chemical weapon)
One contribution of his that is often emphasized in schools and colleges across the world is the “Lewis structure.”
What is the Lewis Structure?
For all intents and purposes, it is a visual representation of how valence electrons are distributed in a chemical compound. It allows us to understand how atoms are connected inside a molecule and also determines reactivity and chemical behavior.
The Lewis structure is particularly handy when trying to predict chemical reactions, as you can easily tell which atoms are going to gain, lose, or share electrons during a reaction. It is also useful to calculate formal charges.
When you consider that the Lewis structure is most often used for understanding molecular bonding, it isn’t surprising to see many high schools feature questions about it on exams. This is done to improve how students understand chemical bonding and molecular geometry.
Students might be asked to draw the CS2 Lewis structure (carbon disulfide) or the structure of any relevant molecule in an exam.
As Proprep states, this would naturally include the typical steps of counting valence electrons, identifying the central atom, drawing single bonds, etc. Knowing these steps is super helpful when students start learning more complex concepts. Let’s explore this further.
The Lewis Structure is Key to Understanding Several Complex Concepts in Chemistry
Molecular orbital theory is one of the many areas where knowledge of Lewis structures is beneficial. Rather than looking at only individual bonds, molecular orbital theory looks at the distributions of electrons in the entire molecule.
We can learn more about our own respiration process with the help of Lewis structures. For instance, if we look at the molecular orbital theory of O2, we can understand how the iron ions present in hemoglobin bind to O2. This gives us insight into how oxygen moves around the body.
It also comes into play in agricultural settings, where understanding the nitrogen triple bond can help explain nitrogen fixation. (This is the process by which bacteria convert N2 into ammonia, which plants are able to absorb.)
There are countless similar areas where Lewis structures help us understand other aspects of our world. Take the material sciences, for instance. We can look at the structure and bonding patterns of materials like graphite and develop or improve similar conductive materials.
The Limitations of the Lewis Structure
It would be wrong not to point out that there are a number of areas where the use of Lewis structures runs into some issues. For one, they ignore molecular shape. This means that you can’t really use them to understand three-dimensional shapes in molecules.
Lewis structures are also not that great when trying to represent resonance, and they can’t provide qualitative information about bond strength or length. You will also run into issues if you try to represent bonding in transition metals with a Lewis structure.
Another point to note is that it won’t give you any information about electron energy levels. Sure, they might show you how valence electrons are arranged. However, this isn’t too helpful if you need to know which electrons are higher or lower in terms of energy levels.
In conclusion, Lewis structures are a great tool that anyone studying chemistry will no doubt use often. Yes, there are limitations to it, but there are alternatives that seek to fill the gaps.
These include balance bond theories, VSEPR theories, electron localization function (ELF), and many more. In the course of learning chemistry, you will undoubtedly make use of the Lewis structure as well as its alternatives to great effect.