Periodic table

Standard atomic weights and isotopic compositions are those of the NIST Physical Measurement Laboratory (Atomic Weights and Isotopic Compositions for All Elements). For the twelve elements whose weight IUPAC gives as an interval (H, Li, B, C, N, O, Mg, Si, S, Cl, Br, Tl) the table uses the IUPAC conventional value. The cells round a weight to at most five significant figures, as the IUPAC periodic table does; the details show every digit. A weight in brackets means the element has no stable isotopes; the number is the mass number of its longest-lived isotope, from americium on that of the isotope PubChem lists, since NIST gives none.

Every other property comes from the PubChem periodic table (National Center for Biotechnology Information): electronegativity on the Pauling scale, the van der Waals radius, the first ionization energy, the electron affinity, oxidation states, melting and boiling points, density, the standard state and the year of discovery. PubChem gives temperatures in kelvin; the table shows °C = K − 273.15 and keeps the kelvin values in the details. Densities of solids and liquids are in g/cm³, those of gases in g/L at 0 °C and 1 atm.

The 18-column form recommended by IUPAC, with the lanthanides (La to Lu) and actinides (Ac to Lr) as two rows of fifteen below the main table. The category colours follow PubChem, which counts hydrogen with the nonmetals and lanthanum and actinium with the lanthanides and actinides. Electron configurations of the superheavy elements are predicted and marked as such; subshells are written in order of shell, as NIST does.

With the keyboard, tab into the table and move with the arrow keys, Home and End. Typing a symbol jumps to it, Enter or Space opens the details and Escape in the details goes back to the element.

Each property is scaled linearly between the lowest and the highest known value, which the legend names. Elements without a reliable value stay grey rather than being guessed. Elements known since antiquity share the colour of the earliest dated discovery.