A short manual. It covers every control, and — more to the point — what each one is for: how morphing the table and mapping properties turns the periodic table from a chart you memorize into patterns you can see. Every RUN button opens the live instrument already set up for that idea.
There has never been one "correct" periodic table. Chemists have folded the same sequence many ways, each exposing a different truth. Switch between them and watch what moves — the elements that travel farthest are the ones whose "home" is genuinely debated. The last one unrolls the table completely.
The familiar 18-column shape. Its honest flaw: the lanthanides and actinides are torn out and parked below, purely so the chart fits on a page. Good for orientation; misleading about where those 28 elements really live.
▸RunThe f-block slotted back between groups 2 and 3, where it chemically belongs. This is the real shape; we only chop it up to save paper. Watch the two detached rows slide up into place.
▸RunRe-sorted by the order electrons actually fill orbitals, which slides the s-block to the right. Its boldest claim: helium sits above beryllium, not above neon — because helium fills an s-orbital just like the alkaline-earth metals. A great argument-starter about what "belongs" with what.
▸See helium moveOne unbroken ribbon winding out from hydrogen. The standard table hides its seams; here you can trace atomic number with your finger and never lift it. Color it by family and the same families sweep past on every loop — that recurrence is periodicity.
▸Trace the threadEach period drawn as a concentric ring, echoing the Bohr shell diagram in the readout panel. One full lap of a ring is exactly one period; the alkali metals all start at the top and the noble gases close each ring. A bridge between the flat chart and the atom underneath it.
▸Go aroundUnroll the whole table into a single row ordered by atomic number, and let the mapped property become height. The everyday 2-D table is really this wave, wrapped so its peaks stack into columns. Map ionization energy and watch the same spike return at every noble gas and the same trough at every alkali metal — the value doesn't drift, it repeats. That repeating function of atomic number is exactly what the word "periodic" means; here it stops being a definition and becomes a shape you can see.
▸See the waveThe table's outline isn't a design choice. The blocks, the torn-out f-block, the left-step ordering — all of it is one thing drawn different ways: the order in which electrons stack into an atom. Here is the machinery underneath every arrangement above.
An electron doesn't circle the nucleus on a track. It occupies an orbital — a fuzzy region where it is likely to be. There are four types, and for the shape of the table only one fact about them matters: how many electrons each can hold.
That one fact is the key the whole app turns on. It is why the
left-step arrangement — which orders elements by the orbital filling next — has the shape it does; why a
shell (one Bohr ring, one period) fills left to right; and why the
electron configuration in a readout reads as shell-number, orbital-letter, count. Click any element and the
“P-BLOCK” tag or the 3p⁵ in its profile is this, made concrete.
§02 showed what the orbitals are and how many electrons each holds. The other half of the story is the order they fill — and that order is the engine behind an element's electron configuration, behind the left-step arrangement (which literally sorts by it), and behind the block sequence itself. It runs by the aufbau principle — lowest energy first.
Madelung predicts the configuration of most elements, but not all — about twenty break it. The two everyone learns sit in the d-block: chromium is [Ar]3d⁵4s¹, not the predicted 3d⁴4s²; and copper is [Ar]3d¹⁰4s¹, not 3d⁹4s². The textbook explanation — that a half-filled and a completely-filled d-subshell are specially stable — is neater than the truth. It doesn't generalize: chromium's heavier twin tungsten is 5d⁴6s², ignoring the half-filled pattern entirely, and the row above tungsten is a mess of exceptions (niobium 4d⁴5s¹, ruthenium 4d⁷5s¹, palladium 4d¹⁰ with an empty 5s). The filled-shell pattern (copper, silver, gold) does hold up; the half-filled one barely does. Neither is magic — both come from how close the 4s and 3d energies sit, plus how electrons of parallel spin lower each other's energy. So the rule is an excellent predictor with real exceptions, and even the tidy story for the exceptions is a simplification worth distrusting. See it play out: open the Left-step table and press Play the orbital fill — chromium and copper flag themselves as it sweeps past.
▸Watch the orbitals fillNearly every section here is about electrons. This one is about the nucleus, and it answers a question the property maps quietly raise: chlorine's mass reads 35.45 — so what is 0.45 of an atom? Nothing. The atomic mass on the table is an average.
Atoms of one element always have the same number of protons, but they can carry different numbers of neutrons. Those variants are isotopes. Chlorine comes as two: chlorine-35 and chlorine-37 (the number is the mass number — protons plus neutrons). A natural sample is a fixed 3-to-1 mix of the two, so the mass on the table is their weighted average — pulled toward 35 because 35 is three times as common.
Argon has 18 protons and potassium 19, so potassium comes later on the table. Yet argon is the heavier of the two (39.95 vs 39.10) — because argon's dominant isotope, argon-40, carries more neutrons than potassium's potassium-39. Weight puts them in the wrong order; proton count puts them right. That single inversion is why the modern table is ordered by atomic number, not mass — the beat the history page is built on, and the anomaly the atomic-mass map flags in Experiment 04.
Color is where the table stops being a list and becomes a map. Each mode paints all 118 elements on one scale at once, so a trend that takes a paragraph to state becomes a gradient you can read in a second. Open any of them, then switch arrangements while the colors hold.
Rises toward the top-right, peaking at fluorine; falls toward the bottom-left. It is how hard an atom tugs shared electrons — fiercest when the nucleus is small and barely shielded.
▸Map itAlso climbs to the top-right and falls down each group. It is the energy to rip off an electron — hardest for the tightly-held noble gases, easiest for the big, loose alkali metals.
▸Map itThe pull a valence electron actually feels — the full nuclear charge minus the inner electrons screening it. Rises across a period, resets down a group. Estimated with Slater's rules from each element's configuration; click an element to see the shielding and net pull drawn out.
▸Map the causePeaks among the central transition metals — tungsten holds out to 3695 K — and collapses at the noble gases. Carbon is the nonmetal that refuses to melt.
▸Find the peakConcentrated in the middle of the d-block — osmium and iridium are the densest things on the chart — and featherweight among the gases up top.
▸Find the heaviesClimbs almost monotonically with atomic number. Spot the rare inversions (argon > potassium) — the reason the modern table is ordered by proton count, not weight.
▸Show the climbAlmost everything is solid. Only two elements are liquid (mercury, bromine); the handful of gases huddle at the top-right. A quick reality check on what the elements are actually like.
▸See the statesMost students learn "ionization energy increases up and to the right" and stop there. Map ionization energy, then switch to effective charge without moving anything else: the two pictures land on almost the same shape. That's not a coincidence — it's the mechanism. The more net positive charge an outer electron feels (Zeff), the harder it is to pull away (ionization energy). Seeing the measured trend and its cause fall on the same gradient is the difference between memorizing chemistry and understanding it. Try it in the wave, too, where both trace the very same sawtooth.
▸Map ionization energy ▸Now map the causeFour trends explain most of chemistry's behaviour. Each comes down to a tug-of-war between how strongly the nucleus pulls and how far away (and how shielded) the outer electrons are. Two words do the heavy lifting below: a period is a row (read left to right across one), a group is a column (read top to bottom down one).
| Property | Across a period → | Down a group ↓ | Why |
|---|---|---|---|
| Atomic radius | decreases → | increases ↓ | More protons pull the same shell in tighter across a row; each new row adds a whole shell further out. |
| Ionization energy | increases → | decreases ↓ | A closer, less-shielded electron is harder to remove. map it → |
| Electronegativity | increases → | decreases ↓ | Small, high-charge atoms grip bonding electrons hardest; fluorine wins. map it → |
| Metallic character | decreases → | increases ↓ | Easily-lost outer electrons make metals; the metalloid staircase marks the hand-off to nonmetals. |
The effective-charge map in §05 showed the nucleus's pull rising across a period as protons pile up. Here is that idea stripped to one variable: take seven species that all carry the same ten electrons, and just keep adding protons. Nothing else changes — so whatever happens to their size is the nuclear pull, and only the nuclear pull.
An ion is an atom that has lost or gained electrons. Line up N³⁻, O²⁻, F⁻, Ne, Na⁺, Mg²⁺ and Al³⁺ and one thing is pinned down: every one has exactly ten electrons — they are isoelectronic. What changes is the proton count, climbing from 7 to 13. More protons pulling on the same cloud draws it in tighter and tighter.
Neon sits dead centre — ten electrons, neutral — yet it is drawn as a dashed marker, not a circle, on purpose. Neon forms no ionic compounds, so it has no ionic radius to measure. Its van der Waals size (~154 pm) comes from a completely different measurement and can't be compared to the ionic radii on either side; drawn to this scale it would falsely make neon the largest of the seven. The honest series is the six ions. One more caveat worth stating plainly: these are Shannon effective ionic radii (6-coordinate). A second common convention — crystal radii — runs about 14 pm larger for cations and smaller for anions (there, Na⁺ is 116 pm, not 102). The shrink is real in either set, but the two must never be mixed, or the trend gets distorted.
The fastest way to learn from the instrument is to ask it a question and watch it answer. The experiments now live on their own page — thirteen of them, from "does helium belong with the noble gases?" to a bag of fertilizer, a dental filling and a bottle of shampoo. Each opens the instrument already set up, and each has its own link you can share.
▸Open the experiments