The role of chemists

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Bradley Pritchard

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          It was Lavoisier who divided the few elements known in the 1700's into four classes, and then John Dalton made atoms even more convincing, suggesting that the mass of an atom was it's most important property.

          In the nineteenth century Johann Döbereiner was the first to attempt to classify elements using their relative atomic mass. He also identified a number of ‘triads’ in the list of elements then known. Each triad was a set of 3 elements that have similar properties (e.g. Cl, Br and I; Ca Sr and Ba).

          In 1863, John Newlands noted that when the known elements were written in order of increasing relative atomic mass, every eighth element has similar properties. He called this the Law of Octaves. (There were only seven elements in each period at this time because the noble gases had not been discovered yet). After 20 elements his table did not make any sense, he had 2 elements in one space because the relative atomic mass values that had been used were incorrect. He was quite close to the right answer.

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          Six years later in 1869 professor Dimitri Mendeleev came up with a periodic table that ours is based on today. A whole new group was added as the noble gasses were found; all the gaps have been filled. Elements are arranged in order of increasing atomic number, rather than relative atomic mass. He amended some relative atomic masses and he also left gaps for undiscovered elements. For the gaps in his table, he predicted the properties of these undiscovered elements. He predicted the properties of an element he called eka-aluminium. He was proved right in ...

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