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Law of Triads
In 1817 Johann Dobereiner noticed that the atomic weight of strontium fell midway between the weights of calcium and barium, elements possessing similar chemical properties. In 1829, after discovering the alkali metal triad of lithium, sodium and potassium he proposed that nature contained triads of elements the middle element had properties that were an average of the other two members when ordered by the atomic weight (the Law of Triads). -
Telluric Screw
In 1862, a French geologist named Alexandre-Emile Béguyer de Chancourtios created 3Dimensional chat of the elements by writing them down in a chart on paper then taping it around a cylinder. The telluric screw plotted the atomic weight the elements on the outside of the cylinder so that one full turn corresponded to an atomic weight increase of 16.The arrangement of the chart meant that certain elements with similar properties appear in a vertical line. He was the first to use an arrangement. -
Law of the Octaves
John Newlands noted that there were similarities between elements with atomic weights that differed by seven, thus he named it after the seven notes in an octave.The "Noble Gases" weren't discovered yet so the periodicity was seven and not eight. This law didn't work for the known elements so it was later dissmissed by the scientific community. -
Basis of the Periodic Table
Dmitri Mendeleev was the first successful attempt to form the basis of the modern periodic table.He did so when he attempted to organise the elements in February 1869, by writing the properties of the elements on pieces of card and rearranging them till he reached the conclusion, by putting them in order of increasing atomic weight and certain types of element regularly occurred.Initially, the table had similar elements in horizontal rows, but he soon changed them to fit in vertical columns. -
Periodic Trends
Julius Lothar Meyer was the first person to recognise the periodic trends in the properties of elements. His first table contained just 28 elements, organised by their valency. These elements were main group elements, but in 1868 he incorporated the transition metals in a much more developed table.This 1868 table listed the elements in order of atomic weight, with elements with the same valency arranged in vertical lines, similar to Mendeleev’s table,his work wasn’t published until 1870. -
X- Ray Spectra
Henry Moseley was a British chemist who studied under Rutherford and developed the use of X-ray spectra to study atomic structure. His research helped arrange elements in a more accurate position in the Periodic Table by a closer determination of atomic numbers. With the discovery of isotopes of the elements, it became apparent that atomic weight was not the significant player in the periodic law but rather, the properties of the elements varied periodically with atomic number.
