VisualChem The interactive chemistry textbook
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The learning path

From atoms to instruments: one coherent path through inorganic, physical, and analytical chemistry. Every lesson puts the observation, the particles, and the equation inside one model you can handle.

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Part I · Matter and atoms

  1. Unit 1 Matter and measurement Chemistry is a quantitative science: every conclusion starts with a reading. This unit begins with units and orders of magnitude, learns to report a measurement honestly (significant figures and uncertainty), identifies substances by density, links the grams you can weigh to the atoms you cannot see with the mole, and finally works out chemical formulas from elemental composition. Units and orders of magnitudeUncertainty and significant figuresDensity: an intensive propertyThe mole: counting atoms by weighingFormulas and composition 5 lessons ≈ 140 min
  2. Unit 2 Atomic structure Why do atoms absorb and emit only particular colours? How do electrons stack into orbitals, and where does the shape of the periodic table come from? This unit answers with spectra, quantum numbers, and electron configurations — and finally counts the protons in the nucleus with X-rays. Inside the atom: protons, neutrons and electronsLight and spectra: the fingerprints of atomsThe quantum model: orbitals and quantum numbersElectron configuration: filling the orbitalsPeriodic trends: size, ionization energy and electronegativityX-rays and atomic number: Moseley’s law 6 lessons ≈ 150 min
  3. Unit 3 Reactions and stoichiometry A chemical equation is an exact recipe: atoms are neither made nor lost, and the coefficients give the ratio of particles. In this unit you write formulas from the charges of ions and name compounds, balance equations, use mole ratios to calculate masses of reactants and products, find the limiting reagent that runs out first, calculate with concentrations and volumes in solution, and predict whether mixing two solutions gives a precipitate, a gas or water. Naming ions and compoundsBalancing chemical equationsMole ratios and mass calculationsLimiting reagents and yieldSolution stoichiometry: concentration, dilution and titrationReactions in aqueous solution 6 lessons ≈ 180 min

Part II · Bonds and structure

  1. Unit 4 Chemical bonds Why do atoms join at all? In table salt, sodium and chlorine are held by opposite charges; in hydrogen, two atoms share a pair of electrons. This unit turns “bonding” from a slogan into an energy account you can compute and check — with potential-energy curves, Born–Haber cycles, Lewis structures and electronegativity. Ionic bonding: opposite charges togetherCovalent bonding: sharing a pairLewis structures and formal chargeBond polarity and electronegativity 4 lessons ≈ 115 min
  2. Unit 5 Molecular shape Why is water bent while carbon dioxide is straight? Shape decides whether a molecule is polar and how molecules attract one another — and through that, boiling points, solubility and life itself. This unit starts from electron-pair repulsion, passes through symmetry, hybrid and molecular orbitals and the colours of conjugated molecules, and ends with the forces between molecules. Valence-shell electron-pair repulsion (VSEPR)Molecular polaritySymmetry and point groupsHybrid orbitalsMolecular-orbital theoryConjugation and colour: π electrons in a boxIntermolecular forces 7 lessons ≈ 220 min
  3. Unit 6 Crystals and solids Why are salt grains little cubes? Why can copper be drawn into wire while diamond is so hard? Why is cadmium sulfide yellow? How much surface does a gram of powder have? This unit starts from unit cells and close packing, uses X-ray diffraction to “see” how atoms are arranged, explains metals, semiconductors and insulators with energy bands, and ends by counting the nitrogen molecules it takes to cover a solid. Lattices and unit cells: bookkeeping for atomsClose packing: ABAB and ABCABCIonic crystals: polyhedra and radius ratiosX-ray diffraction: measuring atoms with wavesMetals and bands: conductors, semiconductors and colourSurfaces and adsorption: counting the molecules that cover a solid 6 lessons ≈ 165 min

Part III · Energy and change

  1. Unit 7 Gases Why does a balloon inflate? What does a thermometer actually measure? Inside a genuinely running molecular-dynamics box you will measure Boyle’s law yourself, watch the Maxwell speed distribution emerge, count molecules through Brownian motion, and find out when real gases stop behaving ideally. Gas laws: where pressure comes fromKinetic theory and the speed distributionMixtures, partial pressures, and effusionBrownian motion: counting molecules under a microscopeReal gases 5 lessons ≈ 125 min
  2. Unit 8 Thermochemistry Why does a hand warmer get hot and a cold pack cold? This unit treats every reaction as an energy ledger: separate system from surroundings and heat from work, measure reaction enthalpies yourself in a calorimeter, use Hess’s law and enthalpies of formation to calculate reactions nobody can measure directly, and finally weigh bond-enthalpy estimates and the energy stored in fuels. Energy, heat and enthalpyCalorimetry: measuring heats of reactionHess’s law and enthalpies of formationBond enthalpies and fuels 4 lessons ≈ 105 min
  3. Unit 9 Entropy and free energy A cold pack absorbs heat yet runs by itself, limestone needs more than 800 °C to decompose, and iron can be smelted with charcoal while aluminium cannot. What decides the direction of a change is not energy alone but entropy — the number of ways energy can be shared out. This unit starts by counting microstates and ends with Gibbs energy, equilibrium constants and the Ellingham diagrams of metallurgy. Entropy: counting the waysEntropy and heat capacity from molecular levelsHeat capacity of solids and third-law entropyGibbs energy: temperature decidesFree energy and equilibriumEllingham diagrams and metal extraction 6 lessons ≈ 185 min
  4. Unit 10 Chemical equilibrium The brown NO₂ in a sealed flask looks perfectly still, yet molecules pair up and split apart countless times a second. This unit starts from a molecule-by-molecule simulation, builds up the equilibrium constant and the reaction quotient, solves equilibrium compositions exactly with ICE tables, tests Le Chatelier’s principle on real colour-changing systems, and finally recomputes the yield — and the compromise — of the Haber process from thermodynamic data. Dynamic equilibrium: both directions at onceThe equilibrium constant and the reaction quotientEquilibrium calculations: ICE tablesLe Chatelier’s principle: how equilibria respondThe Haber process: an industrial compromise 5 lessons ≈ 125 min
  5. Unit 11 Reaction rates Thermodynamics says whether a reaction can happen, not how long it takes. In this unit you time an iodine clock on the virtual bench to find reaction orders, read half-lives from integrated rate laws, extract activation energies from Arrhenius plots, integrate elementary steps to test reaction mechanisms, and finally see how enzymes and metal surfaces speed reactions up by factors of billions. Reaction rates and rate lawsIntegrated rate laws and half-livesCollision theory and activation energyReaction mechanismsFast reactions: relaxation and the diffusion limitCatalysis 6 lessons ≈ 160 min
  6. Unit 12 Phases and solutions Why does ice water sit at 0 °C however hard you heat it? Why does water boil below 90 °C on the Tibetan plateau, why does dry ice never melt, and why does salt melt snow? This unit links heating curves, vapour pressure, phase diagrams and the colligative properties of solutions into one picture — every curve computed from measured data and thermodynamics. Heating curves and the heat of phase changeVapour pressure and boilingPhase diagrams: water and carbon dioxideForming solutions and solubilityColligative properties: freezing, boiling and osmosisBinary phase diagramsSurfactants and micelles 7 lessons ≈ 195 min

Part IV · Reactions in solution

  1. Unit 13 Acids and bases From stomach acid to blood, pH governs chemistry and life. Starting from proton transfer, this unit uses exact equilibrium calculations to explain strong and weak acids, polyprotic speciation, buffers, and titration curves — and ends with you measuring an unknown concentration on the virtual bench. Proton transfer: acids, bases and pHWeak acids and bases: partial ionizationPolyprotic acids and speciationBuffers: resisting pH changeTitration curves and indicatorsWhat makes an acid strong 6 lessons ≈ 150 min
  2. Unit 14 Precipitation and complex ions Hospitals let patients swallow barium — normally a poison — because barium sulfate barely dissolves; ammonia dissolves silver chloride but not silver iodide; a single drop of reagent can pick one ion out of several. This unit ties precipitation, dissolution, separation and identification into one calculable system of solubility products and formation constants, and ends with you identifying an unknown on a virtual bench. The solubility productThe common-ion effect and pHActivities and the salt effectSelective precipitation and separating ionsComplex ions and formation constantsQualitative analysis of cations 6 lessons ≈ 175 min
  3. Unit 15 Redox and electrochemistry Rusting iron, a discharging battery, electroplating and the chlor-alkali industry all move electrons from one substance to another. This unit starts from oxidation-number bookkeeping and balancing redox equations, then uses one table of standard electrode potentials to compute a cell’s voltage, free energy and equilibrium constant, shows how concentration and pH shift potentials and how electrolysis pushes reactions uphill, and finally redraws the whole table as Latimer, Frost and Pourbaix diagrams. Oxidation states: bookkeeping for electronsBalancing redox equations: the half-reaction methodGalvanic cells and standard electrode potentialsThe Nernst equation: concentration and pH shift potentialsElectrolysis: driving reactions with electricityOverpotential and electrode kineticsBatteries: chemistry that stores chargeMaps of oxidation states: Latimer, Frost and Pourbaix diagrams 8 lessons ≈ 240 min
  4. Unit 16 Coordination chemistry Ammonia turns copper sulfate deep blue, haemoglobin holds oxygen on iron, cisplatin kills cancer cells and EDTA measures water hardness — all through complexes of metal ions with ligands. Starting from Werner’s coordination theory, this unit shows how to name complexes and count their isomers, explains their magnetism and colours with crystal-field theory, and measures how stable they are with formation constants and the chelate effect. Complexes and ligandsGeometry and isomerismCrystal-field theory: splitting the d orbitalsMagnetism: counting unpaired electrons with a balanceSymmetry, distortion and the Jahn–Teller effectColour and the spectrochemical seriesElectronic spectra: Δo and B from the bandsStability and the chelate effectHard and soft acids and basesLigand substitution: labile and inertMetal carbonyls and the 18-electron rule 11 lessons ≈ 345 min

Part V · The elements

  1. Unit 17 The main-group elements This is where the periodic table becomes chemistry you can recognise. Why does caesium explode in water while lithium merely fizzes? Why do lead compounds prefer +2? Why is dinitrogen so lazy when nitrogen compounds both feed the world and blast rock? Why is fluorine the strongest oxidant of all? Each question is answered with tools from earlier units — thermodynamic cycles, electrode potentials and acid–base equilibria — and every number is computed from data. Hydrogen and the s-blockBoron, aluminium, carbon, silicon and the inert pairBoranes and clusters: counting skeletal electronsNitrogen and phosphorusOxygen and sulfurHalogens and noble gases 6 lessons ≈ 180 min
  2. Unit 18 Transition metals Steel, copper wire, titanium alloys, catalysts and pigments — the modern world is built of transition metals. This unit explains why they have so many oxidation states and colours, how they are won from their ores, why they make good catalysts, visits the lanthanides, the actinides and the man-made superheavy elements, and ends inside your own blood, where one iron ion carries oxygen. Colours are computed from absorption spectra, and every judgement about smelting and catalysis comes from thermodynamic data. Trends across the d-blockOxidation states and colourExtracting metalsCatalysts and materialsThe f-block and beyondMetals in biology: how haemoglobin carries oxygen 6 lessons ≈ 180 min
  3. Unit 19 Nuclear chemistry Chemical reactions move electrons; nuclear reactions change the nucleus itself, with energies a million times larger. In this unit you draw the chart of nuclides and the binding-energy curve from the NUBASE2020 and AME2020 evaluations, follow the uranium series with the Bateman equations, date rocks and artefacts from isotope ratios, and finally compare fission, fusion and chemical fuels — and learn to read becquerels, grays and sieverts. Nuclear stability and binding energyRadioactive decayHalf-life and radiometric datingFission, fusion and radiation dose 4 lessons ≈ 115 min

Part VI · Measurement and analysis

  1. Unit 20 Measurement data and statistics Every measured result should carry its uncertainty. Starting from the scatter of replicate measurements, this unit covers the Gaussian distribution, confidence intervals and Student’s t; uses t, F and Grubbs tests to decide whether a difference is real; propagates glassware tolerances into a final result; and ends with you building a calibration curve and reporting an unknown’s concentration with its confidence interval and detection limit. Errors, the mean and the Gaussian distributionConfidence intervals and Student’s tComparing results: t tests, F tests and outliersPropagation of uncertaintyCalibration curves and detection limits 5 lessons ≈ 135 min
  2. Unit 21 Spectroscopic analysis Analysts use light to weigh what they cannot see. This unit starts from the Beer–Lambert law, opens up the UV–visible spectrophotometer, watches atoms in flames and plasmas emit and absorb razor-sharp lines, “listens” to molecular vibrations with infrared spectroscopy, and ends by sorting molecules by mass — every band and peak computed from a model and checked against literature and measured data. Light and absorbance: the Beer–Lambert lawThe spectrophotometerFluorescence: how molecules give light backAtomic spectroscopy: emission and absorptionInfrared spectroscopy: molecular vibrationsRotation and vibration: the infrared band of a gasCounting vibrations with group theory: infrared and RamanNMR: listening to hydrogen nucleiMass spectrometry: isotope clusters and fragments 9 lessons ≈ 285 min
  3. Unit 22 Titrimetric and gravimetric analysis Classical chemical analysis still anchors many standard methods. Starting from primary standards and volumetric glassware, this unit measures water hardness with EDTA, computes redox titration curves from the Nernst equation, determines chloride in seawater by argentometry, and ends by heating precipitates to constant mass and watching them lose weight on a thermobalance — every curve and colour computed from equilibrium models, every unknown waiting for you to measure it. Volumetric analysis: primary standards and standardisationKjeldahl nitrogen: from nitrogen to proteinComplexometric titration: EDTA and water hardnessRedox titrationsPrecipitation titration: argentometryGravimetric analysisThermogravimetry 7 lessons ≈ 190 min
  4. Unit 23 Separations and chromatography Real samples are almost always mixtures: separate first, then measure. This unit starts from the partition equilibrium in a separating funnel — why several small extractions beat one large one and how pH decides where an acid or a base goes — then chains extractions into a column to meet retention factors, selectivity, plate height and resolution, and ends at the controls of gas and liquid chromatographs, measuring blood alcohol with an internal standard. Extraction: partition equilibria and the separating funnelChromatography principles: retention, selectivity and RfColumn efficiency: plates, band broadening and resolutionGas and high-performance liquid chromatographyCapillary electrophoresis 5 lessons ≈ 140 min
  5. Unit 24 Electroanalytical chemistry Voltages, currents and conductances are all windows onto chemistry. Starting from reference electrodes and the Nernst slope, this unit explains how glass pH electrodes, ion-selective electrodes and the zirconia oxygen sensor in a car exhaust work, finds titration end points from potentials, explains conductivity through ionic mobilities, counts silver atoms and micrograms of water in coulombs, simulates potential steps and cyclic voltammograms from the diffusion equation, and finally measures dissolved oxygen by titration and with an oxygen electrode — and you calibrate a pH meter yourself. Potentiometry: reference and indicator electrodesThe glass pH electrode and ion-selective electrodesSolid electrolytes: the oxygen sensor in a car exhaustPotentiometric titration: end points from potentialsConductometry: how fast ions moveCoulometry: counting electrons, counting waterVoltammetry: diffusion written in currentDissolved oxygen: the Winkler titration and the Clark electrode 8 lessons ≈ 225 min