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Dobereiner's Triads
Johann Dobereiner grouped triads of elements with similar properties together, such as Li, Na, and K. The middle element's atomic mass is roughly equal to that of the average of the other two. This is also true with the density. He found families like this that seemed to always have three elements, but this was when there weren't as many elements as later. When more and more elements were found, there were more than 3 elements in a single family. This was the main defect in Dobereiner's idea. -
Newlands's Octaves
John Newlands arranged the elements by atomic weight, and he noticed that there were patterns of element similarity in the list. The first and eighth elements were similar, second and ninth, and so on. This was a deeper understanding of the elements than Dobereiner's triads, but very similar. Dobereiner was on the right track, and Newlands was even closer, finding a repeating pattern in atomic masses. -
Lothar Meyer's Table
Meyer, working with the atomic weights of elements, published a 28 element, 6 family table in his textbook of the elements in 1864. The improvement over the people before him was that his table was arranged on valence. He then revised his table in 1869, and it looked almost exactly like Mendeleev's table. The interesting thing was that Meyer made his table by physical properties mostly, and Mendeleev made his by chemical properties. -
Mendeleev's Table
Dmitri Mendeleev published a textbook with a periodic table in in that had a place for all the currently known elements, plus a few extra that were not discovered yet. When he wrote down the properties and atomic weights of the elements on cards and arranged them by atomic weight in rows and columns, he noticed a pattern, similar to what Meyer saw. The pattern only worked if he left spaces in specific places in his table. He, from that, predicted the properties of elements in those spaces. -
Lord Rayleigh Discovers Argon
Lord Rayleigh was working on the atomic weight of nitrogen when he noticed a difference between chemical nitrogen and nitrogen extracted from the air. When working on finding the difference between the two, he published his results and asked the scientific community for an answer to his problem. With William Ramsey, he figured out that the answer was argon, the first discovered noble gas.
Rayleigh won a Nobel Prize in physics for his part in the discovery of argon. -
William Ramsey Finds the Answer to Rayleigh's Problem
William Ramsey contacted Lord Rayleigh about his nitrogen problem and did a couple experiments himself. He isolated argon, the first discovered noble gas. Argon is Greek for "inert". Ramsey won the Nobel Prize in Chemistry for his work in discovering argon. He went on to discover or help discover the last five noble gases, known as helium, neon, krypton, xenon, and radon. -
Henry Moseley and his Contribution to the Periodic Table
Henry Moseley used X-ray spectroscopy to establish a mathematical connection between the wavelengths of the X-rays and atomic numbers of the elements emitting the rays.
He confirmed the atomic numbers which before had only been guessed at because of their place in the periodic table. For example, his mathematical equation proved that cobalt and nickel had the numbers 27 and 28, something assumed before then.
He died in WWI in Turkey at 27. If he hadn't died, he probably would have won the Nobel. -
Glenn Seaborg's Work on Actinides
Glenn Seaborg was an American scientist with the Manhattan Project and found (or co-found) ten elements, from neptunium to nobelium and element 106, which was named Seaborgium in his honor. He also extracted the first visible mass of plutonium during 1942. He also found more than 100 isotopes of known elements, including an isotope of iodine that treats thyroid disease. His actinide theory (and the elements he found) redrew the periodic table to what it looks like today.
