Data sources and methods

Element data

Atomic masses, electron configurations, electronegativity, atomic radius, ionization energy, electron affinity, oxidation states, melting and boiling points, density, standard state and discovery year come from PubChem's periodic table (National Center for Biotechnology Information, U.S. National Library of Medicine). Table positions and discoverer names come from the open Periodic-Table-JSON dataset.

How we work out the numbers students ask for

• Neutrons: the rounded atomic mass minus the atomic number, the way it's taught in class. For synthetic elements we use the mass number of the isotope PubChem lists.
• Valence electrons: the group rule for main-group elements (groups 1–2, and groups 13–18 minus 10; helium has 2). For transition and inner-transition metals we show the outer-shell count and note that inner electrons can also bond.
• Electron shells: counted from the electron configuration by principal quantum number n.
• State at a temperature: compared with the melting and boiling points at standard pressure. Helium has no melting point at 1 atmosphere, so it stays liquid down to absolute zero.
• Common ion charges: the group pattern for main-group elements; PubChem's common oxidation states for the rest.
• Predicted values: elements 109–118 and some configurations are predicted from calculations rather than measured, and are marked.

Animations

The Bohr models place electrons evenly on each shell and spin each shell at its own speed. That's a picture, not physics: real electrons occupy orbitals, which the orbital diagrams show. All animations stop if your device is set to reduce motion.