= Dmitri Mendeleev
{c}
<Dmitri Mendeleev> organized the <chemical elements> by recurring chemical properties and used the arrangement to predict missing entries. His account of the <periodic law> emphasized that gaps and uncertain atomic weights could be tested against similarities within chemical families.<The Periodic Law of the Chemical Elements by Dmitri Mendeleev>[1889 Faraday Lecture: development of the periodic system and predictions of missing elements]{ref}
The method was predictive rather than merely a sorted list: a proposed missing element had to fit several properties at once, including the compositions of its compounds. Modern ordering uses <atomic number>, which distinguishes elemental identity from average isotopic <atomic mass>. Mendeleev's historical atomic-weight ordering and the modern organizing principle should therefore be kept distinct.
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