How to Draw Lewis Structures: Understanding Valence Electron Bonds
Have you ever wondered how electrons bond in molecules? Lewis Structures allow us to visualize these bonds and understand their configurations. Whether you’re a chemistry student or simply curious about chemistry in general, this guide will teach you everything you need to know about creating Lewis structures.
Step-by-Step Guide
Lewis Structures are diagrams that show how atoms bond by sharing electrons in order to fill their outermost shells. Here are the basic steps you should follow to create a Lewis structure:
Step One: Count the Valence Electrons of an Atom or Molecule
The first step in drawing a Lewis structure is determining the number of valence electrons for each atom. Most atoms want to have a full valence shell (8 electrons), except for hydrogen, which wants two electrons in its shell. Start by counting the number of valence electrons your molecule has in total by adding up the valence electrons of each individual atom.
Step Two: Draw a Structure Around the Atoms
Next, draw the atoms in the molecule with their symbols. Put the atom that has the most valence electrons in the center. Connect the other atoms to it with a single bond. You may use dashes or straight lines to depict them. The atomic symbol is written in the center and each valence electron is represented by a dot; draw them in pairs. Single bonds share two electrons, a double bond shares four electrons, and a triple bond shares six electrons.
Step Three: Check All Atoms Have a Full Valence Shell
Count the total number of electrons in the structure you have just drawn. If the structure doesn’t have enough electrons to form a full octet for each atom, try drawing a double or triple bond between atoms to share additional electrons until every atom has a full valence shell.
Step Four: Look for Formal Charges
A formal charge (FC) is the difference between the number of valence electrons on an individual atom and the number of electrons that it is surrounded by in a particular Lewis structure. If the formal charge can be reduced, adjust the position of multiple bonds so that all formal charges on all atoms are zero. Atoms with more negative formal charges indicate the presence of isomers.
Step Five: Identify the Bond Lengths and Angle
The bond length increases as the bond’s strength decreases, i.e. single bonds are longer than double bonds, and double bonds are longer than triple bonds. The Bond angles are determined by the number and arrangement of electron pairs holding the atoms together. In certain molecules, they can fluctuate, resulting in different geometries.
Step Six: Check for Symmetric and Dissymmetric Molecules
If the molecule is symmetric, then all Lewis structures should look identical. If the molecule is dissymmetric, then each possible Lewis structure should be considered and the “average” structure found.
Step Seven: Reinforce Your Drawing with Compatibility Rules
Follow these compatibility rules if there are still multiple solutions: the best fit structure has the most total double and triple bonds, the negative charges are found on more electronegative atoms, and the positive charges are found on less electronegative atoms.
Step-by-Step Drawing Example with Pictures
Let’s illustrate how to draw a Lewis dot structure with a step-by-step example. We will create the Lewis dot structure for carbon dioxide (CO2), an inorganic molecule with two double bonds.
The atomic number of carbon is 6, so it has 6 valence electrons. On the other hand, oxygen has 6 valence electrons, so it has a total of 12 valence electrons. To determine the total number of valence electrons, we add the valence electrons of carbon and oxygen. This results in 16 valence electrons.
The structure of CO2 is such that carbon is in the middle and surrounded by two oxygen atoms. Using this information, draw the structure of CO2.
We have drawn two single bonds (e.g. one pair dots) between the carbon atom and each of the oxygen atoms in the CO2 structure. Each oxygen atom has two non-bonding electrons represented by two dots situated side by side on one corner of a location and one bonding pair. The carbon atom has four non-bonding electrons and two bonding pairs. Because there are not enough electrons for every atom to have eight valence electrons in our starting structure, we will have to draw one double bond. Since the carbon atom has to satisfy 4 more electrons, a double bond between the carbon (C) and one of the oxygen atoms (O) satisfies this. The new, improved structure now has every atom with 8 valence electrons.
Helpful Tips to Remember While Drawing Lewis Structures
There is a lot to remember when drawing Lewis structures. Here are some helpful tips to keep in mind:
- The central atom is usually the least electronegative.
- If there is an atom that can be expanded to have more than 8 valence electrons, usually sulfur, phosphorus, iodine, and xenon, the octet rule may not apply in full.
- In a Lewis structure, the O-H bonds of alcohol, phenol and carboxylic groups can differ, they can be polar, making the compounds stronger acids than expected.
- The formal charge can aid in determining the most likely Lewis structure from a range of options.
Common Mistakes
Drawing accurate Lewis structures can be tricky. Here are some common mistakes you should watch out for:
Common Misconceptions Regarding Atom Valence Electron
- The number of valence electrons is not equal to the number of electrons in the outermost shell of an atom.
- The number of valence electrons can be found using the position of the element in the periodic table.
Examples of Common Mistakes
- Overwriting bonds: With multiple bonds, this mistake is frequent where lone pairs and double bonds are not separated
- Missing lone pairs: Only bonding electrons get counted in valence shell electron pairs repulsion theory (VSEPR), not lone pairs.
- Incorrect formal charges: forgetting to ascertain the most plausible structure or overlooking a charge distribution.
Tips to Avoid Mistakes While Drawing Lewis Structures
- Always count the valence electrons for the atoms in a molecule correctly.
- When assigning the formal charges, consider the electronegativity of the atom, the molecular shape, and the resonance structures of the molecule.
- Draw in the double bonds after the rest of the structure has been established.
Real-Life Examples
Lewis structures can illustrate the bonding between molecules in real-world scenarios. Here are some illustrations:
Step-by-Step Drawing of Lewis Structure of Real-Life Examples with Pictures
Common Mistakes Students Make While Drawing These Real-Life Examples
- Missing or incorrect formal charges in the structure of CH2O
- Incorrect bond order in the N2 structure
Visual Aids
Visual aids, diagrams, and flowcharts can help you understand Lewis structures even more.
Guide for Beginners on Electron Dot Structure Drawing
Common Symbols Used While Drawing Lewis Structure
The following symbols are used while drawing Lewis structures:
- Dots represent valence electrons
- Dashes represent electrons that make up bonds in the molecule
- Bond pairs are depicted with a line between the two atoms
- Lone pairs, represented by two dots next to each other, are a pair of electrons that are not involved in bonding.
Interactive Approach
An interactive approach allows you to apply the concepts learned. Here are some interactive elements you can experiment with to test your Lewis structure knowledge.
Interactive Quiz to Test Your Knowledge After Reading the Article
Time to test your understanding of Lewis Structures with a quiz. Take the quiz here.
Exercises to Help Readers Learn Lewis Structures
Practice is important when it comes to drawing Lewis structures. Here are some exercises that can help you master Lewis structures:
- Draw the Lewis structure for CO
- Draw the Lewis structure for SO2
- Draw the Lewis structure for NH3
Questions to Help Readers Evaluate Their Understanding
- What is a Lewis structure?
- How are valence electrons counted in a Lewis structure?
- What are examples of common mistakes made while drawing Lewis structures?
Common Applications
Lewis structures have many applications in different fields. Here are some of the ways in which Lewis structures are used:
Importance of Lewis Structures in Different Fields
- Chemistry: In chemistry, Lewis structures are essential in understanding chemical bonding, reactivity, and reaction mechanisms.
- Biology: Lewis structures help us understand molecular structure and function in biology.
- Physics: Lewis structures aid physicists in the development of semiconductors and superconductors.
How Lewis Structures are Used in Chemistry, Biology, or Physics
- In chemistry, Lewis structures help predict the polarity of molecules, the basic nature of compounds, as well as the kind of bonds that atoms will form in order to attain full octets.
- In biology, Lewis structures play an important role in predicting and explaining the function of enzymes, DNA, and many other biologically significant molecules.
- In physics, Lewis structures form the basis for the study of atomic structures and properties, as well as chemical bonding and reactivity.
Importance of Lewis Structures in Predicting the Reactivity of Different Molecules
Lewis structures predict the reactivity of various molecules by dividing them into two categories; electrophiles and nucleophiles. Electrophiles are atoms that have empty valence electron orbitals, while nucleophiles contain electron-rich atoms. By identifying these substances, you can quickly guess chemical reactions between electrophiles and nucleophiles.
Ways Lewis Structure Predicts the Molecular Geometry
The arrangement of the electron pairs around the central atom predicts the molecular geometry. With the help of VSEPR Theory, it demonstrates how the electron groups are arranged, and by counting them, the shape of the molecule can be determined.
Conclusion
By following a specific set of steps, drawing Lewis structures can help us visualize the fundamental principles of chemical bonding and molecular structure. Do not hesitate to practice and compound your learnings by doing interactive exercises. Start exercising your knowledge by drawing as many Lewis structures as you can, or by attempting tricky elements like iron and sulfur-containing compounds.
