John Newlands discovered the law of octaves, Meyer and Mendeleev arranged elements based on atomic mass and properties, and Moseley organized elements by atomic number.
John Newlands developed the law of octaves, which suggested that elements could be classified into groups of seven, where properties repeated every seventh element.
Julius Lothar Meyer and Dmitri Mendeleev independently arranged elements based on atomic mass and chemical properties. They left gaps for undiscovered elements, predicting their properties.
H. G. J. Moseley later arranged elements by atomic number, showing that the periodic table is based on atomic number, not atomic mass.
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