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Chemistry · Reference

Periodic Table

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    Use the arrow keys to move between elements, Home and End to move within a row, and Enter to open an element's details. Escape closes them.

    Element details

    Select an element to see its atomic mass, electron configuration, common ions and trend values.

    Data sources

    Values come from the mendeleev Python package, version 1.3.0 (MIT license), which compiles them from published sources:

    • Atomic masses: IUPAC standard atomic weights (CIAAW), rounded to 2 decimal places. Brackets show the mass number of the longest-lived isotope of an element with no stable isotope.
    • Atomic radius: single-bond covalent radius, Pyykkö and Atsumi (2009), in picometers (pm). Every element on the page uses this one radius type.
    • Electronegativity: Pauling scale (CRC Handbook of Chemistry and Physics, as compiled by mendeleev).
    • First ionization energy: NIST Atomic Spectra Database, converted from electron volts to kJ/mol.
    • Electron configurations: measured ground states (NIST). Elements 104 to 118 are predicted.
    • States use melting and boiling points at 25 °C. Common ions follow the main-group rules from the lessons; transition metal charges are the common ones taught in high school.

    Every value was checked against a second source (the public-domain periodictable package and pymatgen). Differences are listed in this activity's README.