Essay -- Papers

IMAGE A BRIEF narration OF THE DEVELOPMENT OF PERIODIC TABLE Although Dmitri Mendeleev is often considered the father of the periodic table, the consort of many scientists contributed to its present form. IMAGE In the Beginning A necessary demand to the construction of the periodic table was the breakthrough of the individual elements. Although elements such as gold, silver, tin, copper, lead and mercury have been cognize since antiquity, the first scientific discovery of an element occurred in 1649 when Hennig Brand discovered phosphorous. During the next 200 years, a vast body of knowledge concerning the properties of elements and their compounds was acquired by chemists (view a 1790 article on the elements). By 1869, a total of 63 elements had been discovered. As the number of known elements grew, scientists began to recognize patterns in properties and began to develop classification schemes. Law of Triads In 1817 Johann Dobereiner spy t hat the atomic weight of strontium fell midway between the weights of calcium and barium, elements possessing similar chemical properties. In 1829, after discovering the halogen triad composed of chlorine, bromine, and unity and 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). This new idea of triads became a frequent area of study. Between 1829 and 1858 a number of scientists (Jean Baptiste Dumas, Leopold Gmelin, Ernst Lenssen, Max von Pettenkofer, and J.P. Cooke) fou... ... varied periodically with atomic number. The question of why the periodic law exists was answered as scientists create an understanding of the electronic structure of the elements beginning with Niels Bohrs studies of the organization of electrons into shells through G.N. Lewis (see a p icture) discoveries of bonding electron pairs. The Modern Periodic Table The last study changes to the periodic table resulted from Glenn Seaborgs work in the middle of the 20th Century. beginning with his discovery of plutonium in 1940, he discovered all the transuranic elements from 94 to 102. He reconfigured the periodic table by placing the actinide serial publication below the lanthanide series. In 1951, Seaborg was awarded the Nobel Prize in chemistry for his work. segment 106 has been named seaborgium (Sg) in his honor.