Periodic Table
Hover an element and its group and period light up, with a line above explaining why its properties come out the way they do. Switch the colour mode to watch electronegativity climb or atomic radius shrink across the table. Drag the temperature slider and the elements melt and boil in front of you.
Sources and accuracy
The numeric properties are drawn from standard reference values (IUPAC, the CRC Handbook of Chemistry and Physics, the NIST databases). For the superheavy elements many quantities are calculated rather than measured, and those are marked as predicted. If you spot an error, tell me and I will fix it.
Frequently asked
Why are there 118 elements?
Because 118 is the last element whose synthesis has been confirmed and accepted by IUPAC. Oganesson was made at Dubna in 2002 and formally named in 2016. Element 119 and beyond exist only as synthesis claims so far.
Why are the lanthanides and actinides pulled out below?
Pure typography: slotted into periods 6 and 7 where they belong, the table becomes 32 columns wide and stops fitting on a page. Switch the layout to "long form" to see the honest version.
What does the cell colour mean?
It depends on the mode. By default colour encodes the category — alkali metals, halogens and so on. Switch "Colour by" to any numeric property and the colour becomes a continuous heat scale with a legend.
Why is the atomic mass of some elements in brackets?
Elements with no stable isotope have no fixed atomic mass: it depends on which isotope you happen to have. For those, convention is to quote the mass number of the longest-lived known isotope.
What is the 3D model on an element page?
There are three. "Atom" is the Bohr model with electron shells taken from the real configuration. "Orbitals" is the |ψ|² probability density cloud for hydrogen-like s, p, d and f orbitals. "Lattice" is the crystal unit cell with real a, b, c parameters.
Mendeleev's periodic system is not a list of substances but a map of regularities. The elements are ordered by nuclear charge, and the rows break exactly where a new electron shell starts to fill. That is why elements in one column share the structure of their outer layer — and, as a consequence, their chemistry.
Left to right across a period the nuclear charge grows, electrons are pulled in harder, the atom contracts and stripping an electron off it gets steadily more difficult: ionisation energy and electronegativity rise. Top to bottom down a group whole shells are added, the outer electrons end up further from the nucleus and screened from it — the atom grows and its metallic character strengthens. Switch the colour mode to radius and to electronegativity to see both trends with your own eyes.
Every one of the 118 elements has a reference page: the full set of physical and chemical properties with the element's rank among all the others, the electron configuration, an isotope table, the discovery story and the origin of the name, plus an interactive 3D model — the Bohr atom, the electron orbitals and the crystal lattice.