All 118 chemical elements with NIST properties: mass, configuration, electronegativity, melting points and more
The periodic table as an API, from NIST data via PubChem (public domain). All 118 elements with the properties that matter: atomic mass, electron configuration, electronegativity (Pauling), van der Waals radius, ionization energy, electron affinity, oxidation states, standard state, melting and boiling points (Kelvin), density, CPK display color, discovery year, group block (alkali metal, noble gas, lanthanide...) — plus the derived period (1-7) and IUPAC group number (1-18, correctly NULL for lanthanides and actinides). Look elements up by atomic number, symbol or name (Au, gold and 79 all resolve — 196.96657 u, melts at 1337.33 K, flanked by its neighbors platinum and mercury). Slice the table any way a chemistry app needs: group=18 returns exactly the seven noble gases, period=2 returns Li through Ne, state=Liquid returns exactly bromine and mercury, group_block=Alkali metal returns the six alkalis. Every response carries an explicit units object so nobody guesses Kelvin vs Celsius. Education platforms, chemistry homework tools, quiz games, lab software, science content — the reference dataset at one token per call.
Every call needs an X-Api-Key header. A free key includes 500 tokens a month, no card required. 1 token per call, so the free plan covers about 500 calls a month.
