Lewis Structure Generator
Enter any chemical formula and instantly get the Lewis dot structure, valence electron count, formal charges, and VSEPR molecular geometry — explained step by step. Need a full reaction mechanism instead? Try the organic chemistry solver.
How the Lewis Structure Generator Works
Drawing a Lewis structure by hand means counting valence electrons, guessing a skeleton, distributing lone pairs, checking formal charges, and starting over when something doesn’t add up. This generator does that work instantly — and shows you every step so you understand the logic, not just the final diagram.
Unlike a generic chemistry chatbot, this tool is built specifically around Lewis structure rules. It counts total valence electrons from the periodic table, builds the most reasonable skeletal arrangement, places bonding and lone pairs to satisfy the octet rule, minimizes formal charge across the structure, and then predicts molecular geometry using VSEPR theory.
What Can the Lewis Structure Generator Draw?
The generator handles the full range of structures covered in general chemistry and Orgo 1, from simple diatomic molecules through polyatomic ions with delocalized charge.
Why Use a Dedicated Lewis Structure Generator?
General-purpose AI chatbots can attempt Lewis structures, but they’re inconsistent with formal charge minimization and frequently get expanded octets or resonance wrong. A dedicated generator applies the same rule set every time.
Understanding valence electron placement is foundational — it’s the basis for predicting geometry, polarity, and reactivity in every later topic, from reaction mechanisms to spectroscopy.
| Tool | Free? | No Signup? | Step by Step? | VSEPR Geometry? | Resonance? |
|---|---|---|---|---|---|
| LewisStructureGenerator (this tool) | Yes | Yes | Yes | Yes | Yes |
| ChatGPT / Claude | Partial | Yes | Inconsistent | Inconsistent | Inconsistent |
| WebQC Lewis Tool | Yes | Yes | No | No | No |
| Mobile apps (database-based) | Partial | No | No | No | Limited |
Built for Every Chemistry Level
The Complete Guide to Drawing Lewis Structures
Lewis structures are the starting point for nearly every concept in introductory chemistry. They show how valence electrons are arranged as bonding pairs and lone pairs, and that arrangement determines molecular shape, polarity, reactivity, and even acid-base behavior. Getting comfortable with the systematic procedure pays off across the entire course.
Step 1: Count Total Valence Electrons
Every Lewis structure starts with a single number: the total valence electrons available. Add up the group-number valence electrons for every atom in the formula. For a polyatomic anion, add one electron per unit of negative charge; for a cation, subtract one electron per unit of positive charge. Getting this number wrong cascades into every later step, so it’s worth double-checking against the periodic table group number before moving on.
For example, in the sulfate ion (SO4 2-): sulfur contributes 6, each of the four oxygens contributes 6 (24 total), and the 2- charge adds 2 more electrons, for a total of 32 valence electrons.
Step 2: Choose the Central Atom and Build the Skeleton
The central atom is typically the least electronegative non-hydrogen atom, since it can support more bonds. Hydrogen and halogens are almost always terminal atoms because they can only form one bond. Connect the central atom to surrounding atoms with single bonds first — this uses two electrons per bond and establishes the skeletal framework before any lone pairs are placed.
Step 3: Distribute Remaining Electrons as Lone Pairs
After the skeleton bonds are drawn, distribute the remaining valence electrons as lone pairs, starting with the outer (terminal) atoms until each satisfies the octet rule, then placing any leftover electrons on the central atom. Hydrogen is the exception — it follows the duet rule and is satisfied with just two electrons (one bond, no lone pairs).
Step 4: Check Formal Charges and Adjust
Formal charge is calculated as: valence electrons − nonbonding electrons − (bonding electrons ÷ 2). The best Lewis structure is the one where formal charges are as close to zero as possible, and any negative formal charge sits on the most electronegative atom. If the central atom carries a large formal charge after the initial pass, converting a lone pair on a terminal atom into an additional bond (forming a double or triple bond) often brings the structure closer to the ideal.
Step 5: Identify Resonance and Expanded Octets
Some molecules and ions have more than one valid Lewis structure that differ only in the placement of double bonds and lone pairs — these are resonance structures, and the real molecule is best described as a hybrid of all of them. Ozone (O3) and the carbonate ion (CO3 2-) are classic teaching examples. Separately, central atoms from period 3 and beyond (S, P, Cl, Xe, and others) can exceed the octet rule, holding 10 or 12 electrons when this lowers overall formal charge — sulfur in SF6 is the textbook case.
From Lewis Structure to Molecular Geometry
Once the Lewis structure is correct, VSEPR (Valence Shell Electron Pair Repulsion) theory predicts the 3D shape by counting electron domains — both bonding groups and lone pairs — around the central atom. Electron domains repel each other and arrange themselves to maximize distance, which is why four domains around a central atom give a tetrahedral electron geometry. Lone pairs occupy more space than bonding pairs, which is why water (two bonding pairs, two lone pairs) is bent rather than linear, even though it also has four electron domains overall.
Common geometries to recognize: two domains give linear (180°), three give trigonal planar (120°), four give tetrahedral (109.5°), five give trigonal bipyramidal, and six give octahedral. When lone pairs are present, the molecular shape name changes even though the electron domain geometry doesn’t — trigonal pyramidal (NH3) and bent (H2O) are both derived from a tetrahedral electron domain arrangement.
Common Mistakes to Avoid
- Forgetting to add or subtract electrons for ionic charge before counting the total
- Placing hydrogen as a central atom (hydrogen can only form one bond)
- Stopping at single bonds when formal charge minimization requires a double or triple bond
- Confusing electron domain geometry with molecular shape when lone pairs are present
- Assuming every period 3+ central atom needs an expanded octet, even when the standard octet already minimizes formal charge
How to Use This Generator Effectively
The most effective way to use this tool is to draw your own structure first, then compare it against the generated result to find exactly where your reasoning diverged — in the electron count, the skeleton, or the formal charge step. Use the optional question field if you want the explanation to focus on a specific point, such as why a particular geometry was chosen over an alternative.