The Periodic Table: Chemistry's Map
118 elements, one chart — and once you see how it's sorted, you can predict chemistry you've never been taught.
Builds on: 0.1 Atoms: The Alphabet of Matter0.2 Electron Shells: Where Electrons Live
Not a list — a map
In 1869 Dmitri Mendeleev sorted the known elements by weight and noticed properties repeating in waves — so he stacked the waves. The result is the periodic table: elements ordered by atomic number Z, arranged so that columns share chemistry. It was such a good map that Mendeleev left gaps and predicted the missing elements’ properties — gallium and germanium showed up years later, matching his guesses almost exactly.
Rows are shells, columns are valence
With Unit 0 behind you, the table’s layout is no longer arbitrary. Each row (period) corresponds to one electron shell being filled: period 1 fills the 2-slot first shell (2 elements), periods 2 and 3 fill 8-slot shells (8 elements each). Each column (group) collects elements with the same number of valence electrons — and since valence electrons are an element’s chemistry, columns behave like families:
- Group 1 — alkali metals (Li, Na, K…): one lonely outer electron, desperate to lose it. Soft metals that hiss, fizz or explode in water.
- Group 2 — alkaline earth metals (Mg, Ca…): two outer electrons, still eager to shed them — just less dramatically.
- Group 17 — halogens (F, Cl, Br, I): one electron short of a full shell, aggressive electron thieves. Fluorine is the most reactive element known.
- Group 18 — noble gases (He, Ne, Ar…): full shells, chemically asleep.
- The wide middle block — transition metals — and the two detached rows below (lanthanides and actinides) fill inner floors of the electron hotel; they are the table’s more intricate districts.
The symbols are international, but their roots are Latin and Greek: iron is Fe (ferrum), sodium is Na (natrium), potassium is K (kalium), tungsten is W (German Wolfram!). No one guesses these — everyone memorizes them. That’s exactly what a memory hook — in German, an Eselsbrücke, a “donkey bridge” — is for: a little story that carries you from the name to the symbol. Every element in the lab below has one in both languages (switch with the EN/DE toggle).
Trends you can read off the map
Two rules of thumb cover most of the table. Moving left → right across a period, the nucleus gains charge and pulls electrons in tighter: atoms get smaller and hold electrons more greedily. Moving top → bottom down a group, new shells stack on: atoms get bigger and their outer electrons easier to steal. That is why the most violent metal (caesium, bottom-left) and the most violent non-metal (fluorine, top-right) live in opposite corners.
⚗️ Lab — The Periodic Table — with a Memory Hook for Every Element
The full map, 118 tiles. Click any element for its data and its memory hook — the little story linking its name to its symbol (in German mode you get the Eselsbrücke instead). The standalone page under 🧪 Elements in the top bar adds a searchable list view.
- Walk down group 1, then across period 3 — watch the categories change color.
- Find the four elements named after the village of Ytterby (Y, Tb, Er, Yb).
- Check the “deceptive” symbols: Na, K, Fe, Sn, Pb, Ag, Au, W, Hg.
Click an element in the table to see its details and Eselsbrücke.
⚗️ Lab — Trend Explorer
The table is not a list, it is a map — and the map has slopes. The first twenty elements, coloured by whichever property you pick. Hover any tile for the exact value.
- Pick Atomic radius and read across period 2: Li to Ne shrinks by a factor of four, even though electrons are being added.
- Switch to Ionization energy. The pattern flips — the small atoms hold on hardest.
- Compare Li, Na and K on all three. Going down a group undoes what going across a period did.