Henry Moseley - In 1913, he used X-ray to order the elements. Each element has a unique emission pattern with X-rayed, Glenn Seaborg - he determined how heavy elements that were rare in the earth fit in the periodic table., John Dobereiner - A German scientist who developed the Law of Triad. Each ttriad wa a group of three elements similar to each other, Lothar Meyer - he published the Modern Theory of Chemistry in which he published the use of atomic weights to group elements., John Newlands - He discerned that the second seven elements repeated the properties on the first seven closely, and he called them Octaves., Dmitri Mendeleev - He realized that the periodic pattern didn't apply to heavier elements. He decided to try to keep the pattern by saving spaces for elements that weren't discovered yet, William Ramsey - He also isolated helium which had been observed in the spectrum of the sun but had not been found on earth, Lord Rayleigh - Through studying nitrogen, found a gas heavier that didn't react with anything. he named it Argon, which means "lazy one" and was the first inert element discovered,

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