# Developement of the Perdiodic table

By kempel

Johann Dobereiner discovers the Law of triads: Chemicals could be grouped in threes based on similar chemical prepares, and when ordered by atomic weight, the middle element had the average atomic weight of the triad.
• # The First Periodic table

Alexandre Beguyer de Chancourtois was the first to formally order the elements by atomic weight. However, as he was a geologist the specifics of his work were mostly disregarded. He was the first to notice periodicity in the physical properties of the elements.
• # Law of Octaves

John Newlands published his law of octaves thoery of ordering the elements: "any given element will exhibit analogues behaviour to the eighth element following it in the table"
Since he likened the periodicity of the elements to music, at first his arrangement was ignored, however it was later recognised when Mendeleev's arrangement predicted unidscovered elements (Newland's also found that the element now known as geranium had not been discovered)
• # Mendeleev's Periodic Table part 1

Dimitri Mendeleev arranged the elements by using individual cards with each element and its properties, arranging them in different pattersn to see which fitted and worked well.
• # Mendeleev's Periodic table part 2

Mendeleev then revised the periodic table to include 8 columns instead of 7 (transitional metals were added) and was able to link the horizontal, vertical and diagonal rellationships of the elements, as well as leaving gaps for predicted elements based on the way some elements didn't fit all patterns, but the differences would accomodate another mid-set of properties.
• # Noble gases

William Ramsay, inspired to investigate by the lectures of Lord Rayleigh, discovered and isolated Argon, the first of the noble or inert gases. The discovery of Argon lead to some confusion as it didn't fit into any of the sections of the (then) periodic table. Later the same year with the help of Lord Rayleigh, William Ramsay was able to discover and isolate the other noble gases: krypton, neon, xenon radon and helium.
• # Moseley's Periodic Table

Henry Moseley was a british chemist who ingeniuosly used X-rays to analyse new and more precise structures and properties of the atoms of elements. He found that the wavelenghts of the x-ray emmisions of the elements linked with the atomic number. he also discovered Isotopes of elements. With this data it became apparent that Atomic Wight was not the key player in the periodic table as all those before him had thought - atomic number was the link to their periodicity.
• # Moseley's Death

When Henry Moseley died in action in WW1, it was such a huge loss to sciecne that the british government decided to excuse scientists from millitary service. Today, The periodic table is based largeley on Moseley's work to do with Atomic Number.