Aristotle, Believed all matter was made of five elements: air, fire, water, earth, and aether (universe), Robert Boyle, Rejected Greek five-element concept; promoted indivisible particles of specific elements; helped solidify atomists' view; believed atoms could change from one element to another, Antoine Lavoisier, Showed oxygen was necessary for combustion; discerned "fire" could not be an element; 33 known elements in his day, Jacob Berzelius, Proposed element symbols using first two letters of the element's Latin name; used superscripts to show how many atoms of an element were in a compound, Johann Dobereiner, Discovered similar properties in groups of elements; groups always seemed to have three elements, thus called triads, John Newlands, Used concept of periodicity to arrange elements by atomic mass; developed the law of octaves; periodic law—properties repeat every so often as atomic mass increases, Dmitri Mendeleev, Arranged elements by atomic mass; left blanks for undiscovered elements; predicted properties of missing elements; placed elements with similar properties in same column; problem: some elements out of order by atomic mass (e.g., Te and I), Henry Moseley, Arranged elements according to atomic number; solved the problem with Mendeleev's table

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