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Period: to
Development of The Periodic Table Time Span
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Johann Dobereiner and The Triads
In 1829 Johann Dobereiner discovered the halogen triad and the alkali metal triad. The halogen triad was made up of elements chlorine, bromine, and iodine. The alkali metal triad was made up of elements lithium, sodium and potassium. After discovering these triads, Dobereiner proposed that in nature there are triads of elements and the middle element contains properties that are an average of the other two members when ordered by the atomic weight. This is now known as the Law of Triads. -
John Newlands and The Octaves
In 1863, an English chemist named John Newlands wrote a paper categorizing the known 56 elements into 11 groups. He distributed them based on similar physical properties. Throughout this process Newlands noticed that many of the pairs of similar elements differed by some multiple of eight in atomic weight. Newlands published his version of the periodic table in 1864. He proposed the Law of Octaves. The Law of Octaves states that any given element will exhibit analogous behavior to the eighth ele -
Lothar Meyer and The Table
In 1864 a German chemist named Lothar Meyer published a textbook that included an abbreviated version of the periodic table that is used to classify elements. This table consisted of half of the known elements listed in order of atomic weight and showed periodic valence changes. Meyer constructed an extended table in 1868. Meyer’s table became available after Medeleev’s table was already publically published. -
Demitri Mendeleev and The Table
In 1869, a Russian chemist named Dmitri Mendeleev became a teacher at St. Petersburg University. While teaching Mendeleev starting writing a textbook on systematic inorganic chemistry. Mendeleev organized his materials in families of the know elements that displayed similar properties. During his time sorting the elements and classifying them Mendeleev noticed pattern in the properties and atomic weights. He observed similarities in the series of Cl-K-Ca, Br-/Rb-Sr and I-Cs-Ba. To sort of this n -
Lord Rauleigh and The Nobel Gases
In 1895, Lord Rauleigh discovered a new gaseous element named argon. Argon proved to be chemically inert. This element did not fit into any one of the known periodic groups. -
William Ramsey and The Nobel Gases
In 1898, William Ramsey suggested that argon be placed into the periodic table between elements chlorine and potassium and in a family with helium. Argon was placed there despite the fact that arong’s atomic weight was grater that potassium. This group was named the “zero” group because the elements of that group have zero valency. Ramsey predicted the discovery and properties of neon accurately. -
Henry Mosely and The Table
In 1913, Henry Moseley determined the atomic number of each element. Moseley made changes and modified the Periodic Law. He changed it so that it would read that properties of the elements vary periodically with their atomic number. When he modified the Periodic Law it put elements tellurium and iodine in the correct order. In 1914, Moseley predicted three unknown elements that would be located between aluminum and gold. He concluded that there were only 92 elements up to and including uranium. -
Glenn Seaborg and The Lanthanide and Actinide Series
In 1940, Glenn Seaborg synthesized transuranic elements, which are the elements after uranium in the periodic table. Uranium was bombarded with neutrons in a cyclotron to produce neptunium. Deuterium and uranium produced plutonium. These new block elements were part of a new block of the Periodic Table called Actinides Series. In 1951 Seaborg was awarded the Nobel Prize.
