The Periodic Table
All 118 elements, raised into a specimen hall by ionization energy, atomic radius, melting point and more.
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CHEMISTRY
Chemistry
Into the microscopic world
Where did the sugar go? Why does iron rust? Follow visible changes into the invisible world of particles.
- 14labs
- 95experiments
- 2articles
Elements and structure
118 elements, electron clouds, molecular shapes and growing crystals: what matter is built from.
4 labs17 experiments
Atomic orbitals and electron clouds
An electron has no path, only probabilities. Watch dots build up into a cloud, then place the electrons yourself.
- 01Electron cloudWhere around the nucleus is the electron most likely to be found?
- 02Orbital shapesWhy does a p orbital have two lobes and a d orbital four?
- 03Radial distribution and nodesIs the electron more likely to be found the closer you get to the nucleus?
- 04Energy levels and aufbauWhy does 4s fill before 3d?
- 05Electron configurationHow should electrons sit in a subshell for the lowest energy?
- 06Quantum numbersCan n, l and m take any values?
- 07Orbital libraryHow many orbitals does shell n have?
Molecular shape lab
Drag the electron pairs around a central atom and watch them spring back to the lowest-energy shape.
- 01Pair repulsionHow do the electron pairs around a central atom spread out?
- 02Hide the lone pairsDoes a molecule with four electron pairs always look like a tetrahedron?
- 03Bond anglesAll three have four pairs. Why is the angle in H₂O smaller than in CH₄?
- 04Hybrid orbitalsHow do carbon’s s and p orbitals become four orbitals pointing to the corners of a tetrahedron?
- 05Molecular polarityIs a molecule with polar bonds always a polar molecule?
- 06Expanded octetsWith five or six pairs around the centre, where do the lone pairs go?
- 07Chiral moleculesCan a molecule and its mirror image be turned until they match exactly?
- 08Molecule libraryCan every row of the shape table be worked out from electron counts?
Crystal growth
Start from a seed and watch fluorite, quartz and other minerals grow faces that follow their own symmetry.
How reactions happen
Molecules must collide hard enough and at the right angle to react; a catalyst gives them another road.
3 labs30 experiments
Microscopic world of reactions
One glowing reaction box: aim molecules at each other, heat, compress, and watch equilibrium form and shift.
- 01Effective collisionsWhen two molecules collide, must they react?
- 02Temperature and activated moleculesAfter heating, has every molecule sped up?
- 03Concentration and pressureSqueeze the gas to half its volume. Why does the reaction speed up?
- 04Reaching equilibriumWhen the concentrations stop changing, has the reaction stopped?
- 05Shifting equilibriumAfter squeezing, heating or adding gas, which way does equilibrium move?
- 06Chain reactionWhy does a little light make a whole batch of HCl?
Catalyst lab
A catalyst gives the reaction a road with a lower barrier: faster, but the same equilibrium.
- 01Another way overDoes a catalyst speed things up by shaving down the barrier?
- 02The surface cycleWhat happens to one N₂ molecule on an iron surface?
- 03Equilibrium stays putDoes a catalyst give you more ammonia?
- 04SelectivityBoth start from CO and H₂. Why does one make methane and the other methanol?
- 05Catalyst poisoningWhy does a trace of sulfur in the feed ruin the catalyst?
Reaction mechanisms: molecular animations
Molecular animations of 19 reactions: where the electrons come from and where they go, with every frame conserved.
- 01Acetic acid + ethanolDoes the oxygen in the water come from the acid or the alcohol?
- 02Ethyl acetate + OH⁻Why does a base hydrolyse an ester completely?
- 03Ethene + bromineWhen the double bond opens, from which side do the bromine atoms add?
- 04Ethene monomersHow do small molecules join into a long chain?
- 05Methane + chlorineWhy is light needed, and is chloromethane the only product?
- 06Copper wire + ethanolThe copper looks unchanged — did it really take no part?
- 07Ethanol + conc. H₂SO₄Same ethanol and acid — why does the product change with temperature?
- 08Benzene + bromineBenzene looks unsaturated — why does it substitute rather than add?
- 09HCl + NaOHWhich particles actually react in neutralisation?
- 10AgNO₃ + NaClHow does a white solid appear from two clear solutions?
- 11Zinc + copper sulfateWhy does the blue fade and red copper grow on the zinc?
- 12Sodium + waterWhere does the hydrogen come from?
- 13Methane + oxygenWhere does the heat of burning come from?
- 14Hydrogen + chlorineIn the pale flame, how do H₂ and Cl₂ become HCl?
- 15Aluminium + iron oxideHow does aluminium pull iron out of its oxide?
- 16Bromoethane + OH⁻Why must the nucleophile attack from the back?
- 17Tertiary halide + waterWhy does SN1 give a pair of mirror-image products?
- 18Bromoethane + OH⁻ (in ethanol)Which H must the base take for a one-step elimination?
- 19Acetic acid + ethanol + H⁺What does H⁺ do in esterification, and where does it end up?
At the bench
Make gases, run titrations, wire up cells: textbook experiments you can carry out step by step.
4 labs33 experiments
Making gases in the lab
Make oxygen and carbon dioxide, then burn charcoal and iron wire in oxygen.
Purifying crude salt
Dissolve, filter, evaporate in twelve steps: watch the salt enter the water, pass the filter paper and crystallise again.
- 01Weigh the crude saltThis 5 g is the prepared sample, not an amount that must all be added to the water.
- 02Measure and transfer waterRead at eye level with the lowest point of the concave meniscus.
- 03Add portions and stir gentlyAvoid striking the sides or bottom of the beaker with the rod.
- 04Stop adding and weigh what remainsUndissolved sand alone does not mean the brine is saturated. Check whether salt grains continue to dissolve.
- 05Fold and open the filter paperIdentify the thicker, triple-layer side. The glass rod will rest gently against it.
- 06Wet the paper and fit it to the wallA good fit helps filtration. Air bubbles mainly slow the flow; they do not necessarily make the filtrate cloudy.
- 07Set up and check the two levelsPosition the receiving beaker so the funnel stem touches its inner wall.
- 08Filter along the rod with three contactsThe filtrate should be clear. If it is cloudy, check for torn paper, an overflowing liquid level or a dirty receiving beaker.
- 09Transfer the filtrate to the dishTwo-thirds refers to volume, not two-thirds of the dish’s height.
- 10Heat and stir continuouslyStirring distributes heat and reduces splashing. Water vapour is invisible; watch the falling liquid level and crystals.
- 11Extinguish and use residual heatDo not keep heating until completely dry, and never blow out a spirit lamp.
- 12Cool, transfer and weighRecord the measured mass. The salt is only partly purified; soluble impurities may remain. Recovery yield is not the same as purity.
Chemical Analysis Lab
Read a burette, run a titration, then identify ions by precipitates, gases and flame colours.
- 01Burette and pipetteIf your eye is a little high or low, how far off is the reading?
- 02Acid–base titrationHow can you find the concentration of a bottle of hydrochloric acid?
- 03Titration curvesWhy does the pH jump suddenly near the equivalence point?
- 04Error analysisDoes a small slip make the measured concentration too high or too low?
- 05Testing for cationsHow do you recognise the metal ion or ammonium in a solution?
- 06Testing for anionsDoes a white precipitate always mean Cl⁻ or SO₄²⁻?
- 07Flame testsWhy is sodium’s flame yellow, while potassium has to be viewed through blue cobalt glass?
- 08Identify an unknown saltGiven an unlabelled bottle of solution, how do you work out which salt it is?
Galvanic and Electrolytic Cells Lab
A galvanic cell turns chemical energy into electricity and an electrolytic cell does the reverse: flip the switch, pull the salt bridge, read the meters.
- 01Hofmann voltameterWhy does one tube always collect twice as much gas?
- 02Copper–zinc cellWith no power supply, why does the ammeter move?
- 03Salt-bridge cellNo electrons pass through the salt bridge, so why does pulling it out stop the current?
- 04Electrolysis in a U-tubeSame current, so why is it sometimes copper and sometimes hydrogen?
- 05Membrane cellWhy does brine electrolysis need a membrane?
- 06Plating and refiningWhen you copper-plate a key, where does the copper come from?
- 07Corrosion tube and manometerAs a nail rusts, does the gas in the tube increase or decrease?
Specimen and materials workshop
Clean a mineral, cast a fossil, pour a crystal cluster: judge first, then act.
3 labs15 experiments
Mineral cleaning and repair lab
Five topics on one bench: identify before you act, brush off dust, remove an iron stain, watch acid eat calcite until the quartz falls, and tell a petroleum jelly shine from a real glued repair.
- 01Five specimensYou do not know what it is yet. Can you wash it anyway?
- 02One soft brushIf you brush more times, does all the mud come off?
- 03Three liquidsCan sodium citrate remove rust? How is it different from a reducing agent?
- 04A beaker of acidQuartz resists acid. Is the whole specimen safe in acid?
- 05One breakIt shines after petroleum jelly. Is the crack repaired?
Fossil moulding and colouring lab
Watch silicone cover an ammonite and peel off as a mould, cast it in plaster and epoxy, check the casts with a caliper, and decide what a coat of colour may claim on a label.
- 01A silicone mouldSilicone is soft. Why can it still get stuck on the master?
- 02A cup of plasterDoes plaster go hard because the water dries out?
- 03Two liquids, A and BDoes extra hardener make it cure faster?
- 04A caliperHow far is the copy from the master?
- 05Three coats of colourThe fossil is brown. Was the living ammonite brown too?
Crystal cluster model lab
Cast a quartz cluster model in clear epoxy: weigh the mix, watch molecules link into a net, compare thin and thick pours, chase bubbles, then tell the model from real quartz.
- 01One digital scaleDoes extra hardener make it set faster?
- 02A net that keeps growingAt what moment does the resin turn from liquid to solid?
- 03Three silicone traysSame resin. Why does a thick pour start to smoke?
- 04One thin streamFast stirring mixes well. So why is the cast cloudy?
- 05Three crystals, one shapeThey look the same. How do you tell it is not quartz?
SHORT READS
Start from everyday questions
Has sugar disappeared when it dissolves in water?
Invisible does not mean absent. The sugar has spread through the water.
Start reading ↓02 / Physical and chemical changesHow is rusting iron different from melting ice?
The key question is whether new substances have formed.
Start reading ↓Has sugar disappeared when it dissolves in water?
Invisible does not mean absent. The sugar has spread through the water.
A sugar crystal contains many sucrose molecules. In water, these molecules gradually leave the crystal and spread among water molecules. They are too small to see, so the crystal shrinks and seems to disappear.
Under ordinary conditions, dissolving sucrose in water is mainly a physical change: the sucrose molecules remain sucrose. If nothing spills or evaporates, the solution’s total mass equals the original mass of the water plus the sugar.
At a given temperature, a fixed quantity of water can dissolve only a limited amount of sugar. Once saturated, additional sugar remains at the bottom. Stirring usually speeds up dissolving, but does not indefinitely increase the amount that can dissolve at that temperature.
Think about it: 10 g of sugar dissolves completely in 100 g of water, with no spilling or evaporation. What is the mass of the solution?
110 g. Dissolving changes how the sugar is distributed, not whether its mass exists.
How is rusting iron different from melting ice?
The key question is whether new substances have formed.
When ice melts, its shape and state change, but it still consists of water molecules. This is a physical change, as is freezing water into ice.
Iron gradually rusts when exposed to water and oxygen. Rust contains substances different from the original iron, so rusting is a chemical change, not simply a change in colour.
A colour change, bubbles or heating can provide clues, but none alone proves a chemical change. Boiling water produces bubbles while remaining water. Always ask whether new substances have formed.
Think about it: which is a chemical change, cutting paper or burning it?
Burning forms new substances, including gases and ash, so it is a chemical change. Cutting changes the shape. This is a conceptual comparison; no fire experiment is needed.