Learn it by doing.
Aufbau computes chemistry from a single energy principle — it holds no library of reactions. This guide is a set of short walkthroughs: type them in and watch each result emerge, from a first bond to a whole synthesis route. Everything below runs on a Mac.
Nothing is looked up.
Every result — a bond that forms, an orbital's shape, an infrared band, a reaction that runs or refuses to — is computed from the model in real time. Reactions resolve to their lowest-energy bonding arrangement from electronegativity, valence, and bond energies; geometry comes from VSEPR and real covalent radii; spectra are read off the same bond graph the engine produces. When the physics can't decide, the app says so rather than inventing an answer. Keep that in mind and everything below makes sense.
The periodic table, then the Tools menu.
Aufbau opens on the periodic table — pick any element to see its shells, orbital configuration, and oxidation states. Everything else lives under the Tools menu (the grid icon in the toolbar); each tool opens in its own space. The walkthroughs below mostly use the Chemistry Workbench (compose reagents, get a verdict and a route) and the Reaction Lab (watch it run live).
Make water from atoms.
The “hello world” of chemistry, computed.
2 H₂ + O₂ → water
- Open Tools ▸ Chemistry Workbench.
- In Enter reagents by hand, type 2 H2 + O2 and tap Add (or tap the Hydrogen and Oxygen tiles).
- Tap Test reaction.
You'll see a green Reacts verdict, Product H₂O, and the change in bonding energy — computed from bond enthalpies, not retrieved.
Enter reactants; watch the product appear.
You're not limited to the tiles — type any formula, or paste a SMILES structure for something a formula can't pin down (rings, functional groups).
Esterification
- In the Workbench, paste the SMILES CCO (ethanol) and add it; then CC(=O)O (acetic acid).
- Tap Test reaction.
Cold, Aufbau reports no reaction — and that is the honest answer rather than a missing feature. Esterification is bond-for-bond identical to its reactants: the same bonds appear on both sides, so the computed ΔH is exactly zero and there is nothing for an energy model to prefer. The ester is enumerated as a candidate; it simply cannot be chosen on energy alone. Turn the temperature up and a dehydration takes over instead — a real, entropy-driven channel in which one molecule becomes two. Pick any product's Product pill to point the 3-D view, NMR, and retrosynthesis at it.
Tip: the temperature and pressure dials matter. The same mixture can be inert cold and reactive hot; squeezing a reaction that changes its mole count shifts the balance. A catalyst (Fe / Pt / Pd) removes a kinetic barrier — a downhill-but-stuck reaction proceeds; an uphill one still won't.
From reagents to product, step by step.
When a mixture reacts in more than one step, the Workbench shows the Pathway — each step's mechanism and its energy change — derived by iterating the engine to a stable end point. The classic example is the real industrial route to urea, the world's most-used nitrogen fertilizer.
Urea from CO₂ + ammonia
- In the Workbench, type CO2 + 2 NH3 and Add.
- Tap Test reaction and read the Pathway card.
The result — Product, ΔH, 3-D, spectra — follows to where the chemistry settles: urea (CH₄N₂O) + water.
Tell it what you want; it finds what you need.
This is the reverse question — and Aufbau answers it from first principles. Mark one reactant as a wildcard: an element with a question mark, like N? for “a nitrogen source.” Name the product you want, and the engine reasons backward to the reactant you're missing — then proves it against the real route.
“I have CO₂. What makes urea?”
- In the Workbench, type CO2 + N? and Add. CO₂ becomes a reagent; N? becomes a wildcard.
- Enter the target CH4N2O and tap Find.
- Tap Use to drop the answer in and run the reaction.
It doesn't guess and it doesn't just scan. Aufbau derives that you need an NH₃‑type source — two of them, with water leaving — then confirms Ammonia ×2 → CH₄N₂O against the real route engine. Under Also tried it rules out the rest honestly (nitric acid, nitrogen: no reaction; methylamine: an N‑methyl product, not urea).
A confident “no reaction” is a feature.
Most tools always hand you a product. Aufbau abstains when no favorable transformation exists — and tells you how close it came.
Nitrogen + oxygen, cold
- Type N2 + O2 and Add. Leave the temperature low.
- Tap Test reaction.
An amber no reaction verdict, with the nearest rearrangement it considered and why it's uphill — the reagents are simply more stable. (Air doesn't spontaneously burn; the model agrees.)
Retrosynthesis, validated as it goes.
Give the engine a target and it proposes strategic disconnections — then validates each one against the same forward model that would run the synthesis, keeping only cuts it can itself reverse. No library of transforms.
Take a molecule apart
- Build or recall a product in the Workbench (try Benzene, or type C4H10).
- Tap Retrosynthesis of … under the result.
You get a disconnection tree down to buyable building blocks — an aromatic ring stays whole (you build onto it, not take it apart); butane cuts at its central C–C bond, the strategic choice.
The reactor, running.
The Reaction Lab is the engine running live: reactant molecules share a box, interact all at once, and settle into products. Use the temperature slider, or Cool down / Heat pulse, to push a mixture over (or under) its barriers. From any result, See in 3-D opens the products as real structures you can rotate — VSEPR geometry, true bond lengths, aromatic π-clouds, metal electron seas — and Energy draws the reaction's profile: reactants, the activation hump, products.
Send a mixture across: from the Workbench, Run in Reaction Lab hands your reagents to the live reactor so you can watch the same reaction you just predicted actually play out.
Ask for a shape. Find out what it costs.
Everywhere else in Aufbau you ask a question and read an answer. Sculpt runs the other way: you state the geometry a design needs — this angle, that metal–donor distance, this torsion — and the engine drives the molecule toward it and reports the strain. Where a target fights the chemistry, the chemistry wins, and the tool tells you by how much rather than quietly complying.
Wrap a crown ether, then squeeze it
- Open Tools › Sculpt and load a flexible ring — 18-crown-6 is the classic.
- Under Coordination, add its six oxygens as donors. The ligand wraps around the ion.
- Drag the M–donor slider outward and back. Watch the reached distances track your request.
- Now pull it in tight, to about 2 Å, and read the line underneath.
The readout turns orange: “The ligand did not reach this sphere — it complied under strain, so this radius says nothing about whether the ion fits.” That refusal is the point. A design tool that satisfies every target you type is not helping you — it is agreeing with you. Sculpt reports the miss in Ångströms so you can tell a shape the molecule will hold from one it only tolerates.
One engine, many views.
Spectra — IR & NMR
IR Normal Modes builds and diagonalizes the mass-weighted Hessian, so bond motions mix into true normal modes. Proton NMR reads hydrogen environments straight off the structure — shifts, multiplicities, integrals. Both are a view of the bond graph, computed, never stored.
Orbitals, spin & qubits
For H/C/N/O molecules, an extended-Hückel treatment draws the HOMO/LUMO and spin density as real wavefunction lobes. The quantum tools carry that into spin: unpaired electrons as qubits, and a diamond nitrogen-vacancy center you read with light.
Nuclear
Step outside ordinary chemistry to change the nucleus — decay, transmutation, breeding chains. The route from mercury to gold is forced into its real two-step path by the arithmetic of binding energy, and the same physics powers the thorium water-splitter in the Lab.
Carbon under pressure
Squeeze graphite and watch its Gibbs energy fall until diamond wins — Le Châtelier by molar volume, with the crossover pressure computed live as you turn the dial.
Reagent shelf
A stockroom of common reagents — acids, bases, oxidizers, gases, organics, salts — each shown with its real structure. Tap one straight into a mixture. This is also the pool the wildcard solver searches.
Explore the periodic table
Every element's shells, orbitals, and oxidation states — and a configuration filter to go beyond the known table. The same aufbau rule fills any Z.
Deterministic, reproducible, and honest when unsure.
Aufbau is AI — but not a language model. Every result is computed from a fixed physical model, so the same input always gives the same answer, traceable to the energy that produced it. It guarantees reproducibility and honesty, not omniscience: where a simple model reaches its limit it abstains rather than fabricate. It runs entirely on your device, collects nothing, and makes no network connections — see the Privacy page. Questions or ideas? The Support page has the way in.
