Lewis dot structures for molecules and polyatomic ions
Lewis Structures draws the Lewis structure of a molecule or polyatomic ion from its formula. Type H2O, CH4, NO3- or SO4 2- and it builds the correct structure around the central atom, with lone electrons as dots, formal charges if you want them, and its resonance structures. Molecules with more than one central atom, like ethanol, acetic acid, HNO₃ or N₂H₄, come from a list you can pick from or type by name or formula.
Teachers use it for three kinds of question: draw the structure, complete it from the skeleton or from the bonds, or find the mistakes in a wrong one. Change a bond, an atom’s lone electrons or its formal charge by clicking the figure, and the generator checks the result and lists its mistakes as sentences, like “O has 10 electrons around it”, for the answer key.
What you can set
- The formula or name: main-group elements through period 5 with one central atom, or a molecule from the list
- A flat, textbook-style drawing, or shaped to hint at the real shape (like bent H₂O)
- Bonds as lines or as pairs of dots, and formal charges shown or not
- The octet rule or fewest formal charges, for ions like SO₄²⁻ where textbooks disagree
- One resonance structure, or all of them joined by ↔
- The question: the full structure, bonds only, or the skeleton, or changes for a find-the-mistake question; a chart title and an answer key
Copying, printing and sharing
Copy the figure straight into a test, worksheet or slide, or download it as a PNG or SVG. Printing the page prints
just the figure. Share link copies the page’s address with your settings in it, so anyone who opens it sees this
exact figure, and presets save settings you use often in your browser. It’s free, with no sign-up.
Frequently asked questions
How do I type a formula with a charge?
Put a space or ^ before a charge of 2 or more, like SO4 2- or PO4^3-. A charge of 1 can go straight after the formula, like NO3- or NH4+.
Which structure does it draw for SO₄²⁻?
Textbooks disagree, so you choose. The octet rule, the default, gives every atom eight electrons, with formal charges where needed. Fewest formal charges lets atoms in period 3 and lower have more than eight, adding double bonds until the formal charges are as small as they can be. The mistake check follows whichever rule you pick.
Can it draw resonance structures?
Yes. For a molecule or ion like O₃ or NO₃⁻, show one resonance structure and pick which, or show all of them in a row joined by ↔.
How do I make a find-the-mistake question?
Open Changes, then click an atom or bond in the figure, or use the list, to change a bond’s order, an atom’s lone electrons or formal charge, the brackets or the central atom. The generator lists what is now wrong, and the answer key prints those mistakes under the figure. A change that leaves the structure correct, such as one that makes another resonance structure, isn’t a mistake.
What can’t it draw?
Transition metals, and ionic compounds like NaCl, which aren’t one Lewis structure. A molecule with more than one central atom has to be on the list; if yours isn’t, the Request it button asks us to add it.
Chemistry Figures Lewis Structures