← Periodic table

Sources and methodology

Where the data in Mendeleev comes from, and how the pages on the 118 elements are written.

Methodology

The element profiles (where the element is found, how it is produced, what it is used for, its role in living things, its hazards, its history) are educational rewrites, written for adults who are not chemists.

Physical values (atomic mass, density, melting and boiling points, Pauling electronegativity) are rounded reference values at 1 atm; the state shown is the one at 0 °C. For an element with no stable isotope, the mass shown is the mass number of its most stable isotope.

Prices are orders of magnitude for the pure element, in US dollars per kilogram: they vary widely with purity, form and market.

Half-lives of never-observed nuclides are estimates from systematics (Viola–Seaborg, Sargent, Myers–Swiatecki, Gamow) fitted to NUBASE2020: they are flagged as such in the app.

To check a profile, each element links to its Wikipedia articles (English and French) and its Wikidata entry.

Element properties

• National Institute of Standards and Technology, Atomic Spectra Database — Ionization Energies. First ionization energies.
• J. C. Slater, “Atomic Radii in Crystals”, J. Chem. Phys. 41, 3199–3204 (1964). Empirical atomic radii.
• E. Clementi, D. L. Raimondi, W. P. Reinhardt, “Atomic Screening Constants from SCF Functions. II”, J. Chem. Phys. 47, 1300–1307 (1967). Calculated atomic radii, where no empirical value exists.
• J. A. Johnson, “Populating the periodic table: Nucleosynthesis of the elements”, Science 363, 474–478 (2019). Cosmic origin of the elements: Big Bang, stars, supernovae, neutron star mergers, cosmic rays.

Prices and raw materials

• Wikipedia, “Prices of chemical elements”. Indicative prices of the pure element (orders of magnitude).
• U.S. Geological Survey, National Minerals Information Center. Indicative prices of the pure element (orders of magnitude).
• Regulation (EU) 2024/1252 of the European Parliament and of the Council of 11 April 2024 (critical raw materials). Elements listed as critical or strategic raw materials by the European Union.

Nuclei and isotopes (physicist mode)

• F. G. Kondev et al., “The NUBASE2020 evaluation of nuclear physics properties”, Chin. Phys. C 45, 030001 (2021). Known nuclides of each element: half-lives, decay modes, spins, abundances (physicist mode, chart of nuclides).
• W. J. Huang et al., “The AME 2020 atomic mass evaluation (I)”, Chin. Phys. C 45, 030002 (2021). Atomic masses of nuclides and binding energies.
• M. Wang et al., “The AME 2020 atomic mass evaluation (II). Tables, graphs and references”, Chin. Phys. C 45, 030003 (2021). Atomic masses of nuclides and binding energies.
• N. Wang, M. Liu, X. Wu, J. Meng, “Surface diffuseness correction in global mass formula”, Phys. Lett. B 734, 215–219 (2014). Masses of never-observed nuclides (pale cells on the chart of nuclides), calibrated against AME2020.

Particles and their passage through matter (physicist mode)

• S. Navas et al. (Particle Data Group), “Review of Particle Physics”, Phys. Rev. D 110, 030001 (2024). Masses and lifetimes of Standard Model particles.
• D. E. Groom, Particle Data Group, “Atomic and Nuclear Properties of Materials” (2024). Radiation and interaction lengths, critical energy, passage of particles through each element.
• KATRIN Collaboration, “Direct neutrino-mass measurement based on 259 days of KATRIN data”, Science 388, 180–185 (2025). Upper limit on the electron neutrino mass.