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Discovery of Elements
Elements had to be discovered before the periodic table could be created. The first element scientifically discovered was phosphorous in 1669 by Hennig Brand. By 1869, 63 elements had been discovered. -
Johann Dobereiner begins research
Johann Dobereiner noticed that the atomic weight of strontium fell midway between those of calcium and barium, which have similar chemical properties -
Creation of Law of Triads
In 1829, after discovering the halogen triad composed of chlorine, bromine, and iodine and the alkali metal triad of lithium, sodium and potassium Dobereiner propsed that there were triads of elements. He also stated that when put in order by atomic weight, the middle element had properties that were an average of the other two. -
Period: to
Law of Triads
Multiple scientists began researching the law of triads and discovered that these types of chemical relationships extended beyond the triad. Also, fluorine was added to the halogen group; oxygen, sulfur,selenium and tellurium were grouped into a family while nitrogen, phosphorus, arsenic, antimony, and bismuth were classified as another. -
Newlands Begins Research
John Newlands wrote a paper that divided the 56 established elements into 11 groups based on similar physical properties also noting that many pairs of similar elements existed which differed by some multiple of eight in atomic weight. -
Law of Octaves
In 1864, Newlands published his version of the periodic table and proposed the Law of Octaves. This law stated that any given element will exhibit analogous behavior to the eighth element following it in the table. -
Lothar Meyer works on creating a Periodic Table
in 1864, Lothar Meyer wrote a textbook that included a rather abbreviated version of a periodic table used to classify the elements. This consisted of about half of the known elements listed in order of their atomic weight and demonstrated periodic valence charges as a function of atomic weight. His Periodic Table would be published later in 1870 -
First Periodic Table Designs
A.E.Beguyer de Chancourtois created an ordering of chemical elements demonstrating the periodicity of chemical and physical properties, published in 1869. -
Mendeleev's Periodic Table
When Mendeleev arranged his cards on a table in order of ascending atomic weight grouping elements of similar properties together he ccreated the Perioidc Table. -
Dmitri Mendeleev works on creating a Periodic table
Mendeleev noticed patterns in the properties and atomic weights of halogens, alkali metals and alkaline metals. He observed similarities between the series Cl-K-Ca , Br-/Rb-Sr and I-Cs-Ba. In an effort to extend this pattern to other elements, he created a card for each of the 63 known elements. Each card contained the element's symbol, atomic weight and its characteristic chemical and physical properties. -
Discovery of Noble Gases
In 1895 Lord Rayleigh reported the discovery of a new gaseous element named argon which proved to be chemically inert.This element did not fit any of the known periodic groups. -
William Ramsey Contributes to Noble Gases
In 1898, William Ramsey suggested that argon be placed into the periodic table between chlorine and potassium in a family with helium, despite the fact that argon's atomic weight was greater than that of potassium. This group was termed the "zero" group due to the zero valency of the elements. -
Henry Moseley Contributes to Table
In 1913, Henry Moseley published the results of his measurements of the wavelengths of the x-ray spectral lines of a number of elements. This showed that the ordering of the wavelengths of the x-ray emissions of the elements coincided with the ordering of the elements by atomic number. It became apparent that atomic weight was not the significant player in the periodic law and instead, properties of the elements varied periodically with atomic number. -
Most Recent Major Changes to Table
Starting with his discovery of plutonium in 1940, Glenn Seaborgg discovered all the transuranic elements from 94 to 102. He also reconfigured the periodic table by placing the actinide series below the lanthanide series.
