Home / Learn / Chemistry / Lewis structuresTool #L47 (formerly #1102)

Lewis structures

Count the valence electrons, tap bonds to make them single, double or triple, and watch the lone pairs, formal charges and octets update. Get the best Lewis structure and every resonance form for 29 molecules and ions (H₂O, CO₂, O₃, NO₃⁻, CO₃²⁻, SO₄²⁻, CO, N₂O …) or build your own, with the steps written out.

Keep it one tap away for everyday use.

Bookmark Lewis structures?

Press Ctrl + D now. Your browser opens its own bookmark box, where you choose the name and folder.

  1. Count
  2. Tap bonds
  3. Octets
  4. Resonance
Nothing is uploadedWorks offline once open

Draw the Lewis structure

Tap a bond to change it: single → double → triple → single. Lone pairs move to match.

    How to draw one, step by step

      Try this

      • Pick CO₂ and press All single bonds. Carbon is short of electrons. Tap bonds until every atom has 8.
      • In nitrate, NO₃⁻, press Next resonance form: the double bond moves, nothing else changes. The real ion is an average of all three.
      • Try carbon monoxide: the best structure has a triple bond, and carbon carries the minus charge even though oxygen is more electronegative.
      • Pick SO₄²⁻ and tick Allow expanded octets. Which version has smaller formal charges?
      • Build your own: N with H H H H and charge 1+. Where is the plus charge?

      Check yourself

      Type a whole number for each, then press Check. New questions every time; nothing is saved.

      What it does

      A Lewis structure (electron dot structure) shows every valence electron in a molecule: shared pairs as bonds, the rest as dots. This page counts the electrons for you, places the lone pairs, and lets you tap a bond to change it from single to double to triple. At once you see whether every atom has its octet (2 for hydrogen), the formal charge on each atom, and whether you have found the best structure. For ions like nitrate it shows each resonance form.

      It follows Class 10 Science (carbon and its compounds: electron dot structures of H₂, O₂, N₂, CH₄ and CO₂) and the Class 11 Chemistry chapter on chemical bonding (the Kössel–Lewis approach, formal charge, resonance and the limits of the octet rule). Switch Level to Class 10 to hide formal charges and resonance. Next, see the 3D shape with the VSEPR shape viewer tool; for rings and double bonds from a formula use the unsaturation.

      How to use it

      1. Pick a Molecule or ion, or Build your own: choose a central atom, type the outer atoms with spaces (e.g. O O O) and choose the charge.
      2. The grey box shows the valence electron count with the live numbers.
      3. Tap a bond in the picture to change it. Lone pairs are placed for you: outer atoms are filled to 8 first, then the central atom.
      4. Read the result: red rings and messages show any atom that is short of, or over, its octet. “Best structure” means every rule is met with the smallest formal charges.
      5. Best structure jumps to the answer, Next resonance form steps through equal forms, All single bonds starts again.
      6. Allow expanded octets lets atoms from period 3 down (S, P, Cl …) take double bonds beyond 8 electrons when that lowers the formal charges.

      Worked example: the nitrate ion, NO₃⁻

      Valence electrons: N 5 + O 6 × 3 + 1 (charge 1−) = 24. Three single bonds use 6, leaving 18; each oxygen takes 6 as lone pairs, so nitrogen has only 6 electrons. Turning one oxygen lone pair into a second bond gives nitrogen its octet. Formal charges: N = 5 − 0 − 4 = +1; the double-bonded O = 6 − 4 − 2 = 0; each single-bonded O = 6 − 6 − 1 = −1. They add up to −1, the charge of the ion. The double bond can be on any of the three oxygens, so there are 3 resonance forms and the average N–O bond order is 1.33: in the real ion all three bonds are the same length.

      Tips

      • Formal charges always add up to the overall charge. Use that to check your sums.
      • B, Be and Al are happy with fewer than 8 (BF₃ has 6 round boron). Atoms in period 2 (C, N, O, F) can never have more than 8.
      • An odd total (NO₂ has 17) means one atom must have 7: a free radical.

      FAQ

      Is the Lewis structure of O₂ wrong? It pairs every electron, but oxygen is attracted to a magnet because it has two unpaired electrons. Molecular orbital theory explains that; Lewis structures cannot.

      Does the tool handle any molecule? It handles the listed examples (including chains like ethene and methanol) and any molecule with one central atom. Skeletons with several central atoms are given as examples only.

      Is this an NCERT tool? No. It is a free fibub page written to help with these topics. Everything runs on your device.

      Where the numbers come from

      • Lewis structure rules (octet and duet, formal charge = valence electrons − lone electrons − bonds, smallest formal charges with minus charges on the more electronegative atom, resonance) are general chemistry, written fresh for fibub.
      • Pauling electronegativities and valence electron counts: general chemistry facts (periodic table).
      • Checked against the Lewis structures quoted in general chemistry texts for 29 molecules and ions: bond orders, formal charges (CO: C −1, O +1; O₃: centre +1; NH₄⁺: N +1), 3 resonance forms for NO₃⁻ and CO₃²⁻ with average bond order 4/3, 6 expanded-octet forms for SO₄²⁻ with average 1.5, the incomplete octet of BF₃ and the odd electron of NO₂.

      Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.

      Last updated 2026-11-09.

      Change log for Lewis structures

      1. Add #1102 Lewis structures and formal charge Details on GitHub

      Every change to fibub

      Related tools

      18-electron rule #T107 Pick the metal, the charge and the ligands (CO, phosphines, halides, Cp, arenes, allyl, hydride, oxo and more) to get the valence electron count, the metal's oxidation state, its dⁿ count and the L/X bond classification, with both the covalent and ionic counts and 15 textbook examples. Unsaturation #T572 Type a molecular formula (C8H10N4O2, C5H6N+) or paste a SMILES string and get the rings plus double bonds (double bond equivalents), whether the formula has an even number of electrons, the nitrogen rule, the monoisotopic, nominal and average masses, and every combination of rings, double and triple bonds that fits. Handles halogens, N, P, S, O, Si, B, charges and isotope labels. VSEPR shape viewer #L46 Add bonded atoms and lone pairs to a central atom and watch the 3D shape change: linear, bent, trigonal planar, pyramidal, tetrahedral, see-saw, T-shaped, square planar and octahedral. Turn it with your finger, read the ideal bond angle and the hybridisation, count the pairs from any formula, and test yourself. MO diagram #L48 Pick a diatomic molecule or ion from H₂ to Ne₂ (O₂, O₂⁺, O₂⁻, N₂, B₂ …) and fill its molecular orbitals one electron at a time. See the energy diagram, the bond order with the working, unpaired electrons, whether it is paramagnetic, and what s–p mixing changes. With a table across the period and practice questions. IUPAC namer #L49 Build a carbon chain of up to 10 carbons, tap carbons to add methyl and ethyl branches, add a double or triple bond and one functional group (–OH, –CHO, C=O, –COOH, –Cl, –Br). Get the IUPAC name with each step explained, the molecular formula and the homologous series, and test yourself on new structures. Dipole polarity #L54 Pick a molecule, see each bond dipole as an arrow from the electronegativity difference, and watch them add up or cancel on the 3D VSEPR shape. Swap outer atoms (CH₄ to CH₃Cl to CCl₄), compare with measured dipole moments, see why NF₃ is far less polar than NH₃, and test yourself. Bond enthalpy estimator #L222 Pick a reaction or count the bonds yourself and estimate its enthalpy change: energy in to break the old bonds, energy out when the new bonds form, ΔH = broken − made. An energy ladder shows the climb to separate atoms and the drop to products, with every number filled in. Markovnikov addition predictor #L225 Pick an alkene (propene, but-1-ene, 2-methylpropene and more) and add HBr, HCl, HI or water with acid. See the two carbocations that could form, which is more stable and why (inductive effect and hyperconjugation), the product and its IUPAC name, and how a peroxide flips HBr to anti-Markovnikov. Ring directors #L226 Put –OH, –NH₂, –OCH₃, –CH₃, –Cl, –Br, –NO₂, –CN, –CHO or –COOH on a benzene ring, then nitrate, brominate or chlorinate it. See where the new group goes, whether the ring reacts faster or slower than benzene, the resonance structures that explain it, and the IUPAC names of the products. Hydrogen bonding #L228 Watch water molecules jostle as hydrogen bonds break and re-form, cool them below 0 °C to lock them into an open ice lattice with four bonds each, and see why ice floats. Then sort molecules such as NH₃, HF, CH₄, H₂S and methoxymethane into those that hydrogen bond and those that do not, with the reason.