Although Dmitri Mendeleev is often considered the "father" of the periodic table, the work of many scientists contributed to its present form. In the Beginning
A necessary prerequisite to the construction of the periodic table was the discovery of the individual elements. Although elements such as gold, silver, tin, copper, lead and mercury have been known 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 (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 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 halogen triad composed of chlorine, bromine, and iodine 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 popular 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) found that these types of chemical relationships extended beyond the triad. During this time 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. Unfortunately, research in this area was hampered by the fact that accurate values of were not always available. First Attempts At Designing a Periodic Table
If a periodic table is regarded as an ordering of the chemical elements demonstrating the periodicity of chemical and physical properties, credit for the first periodic table (published in 1862) probably should be given to a French geologist, A.E.Beguyer de Chancourtois. De Chancourtois transcribed a list of the elements positioned on a cylinder in terms of increasing atomic weight. When the cylinder was constructed so that 16 mass units could be written on the cylinder per turn, closely related elements were lined up vertically. This led de Chancourtois to propose that "the properties of the elements are the properties of numbers." De Chancourtois was first to recognize that elemental properties reoccur every seven elements, and using this chart, he was able to predict the the stoichiometry of several metallic oxides. Unfortunately, his chart included some ions and compounds in addition to elements. Law of Octaves
John Newlands, an English chemist, wrote a paper in 1863 which classified the 56 established elements into 11 groups based on similar physical properties, noting that many pairs of similar elements existed which differed by some multiple of eight in atomic weight. In 1864 Newlands published his version of the periodic table and proposed the Law of Octaves (by analogy with the seven intervals of the musical scale). This law stated that any given element will exhibit analogous behavior to the eighth element following it in the table. Who Is The Father of the Periodic Table?
There has been some disagreement about who deserves credit for being the "father" of the periodic table, the German Lothar Meyer (pictured here) or the Russian Dmitri Mendeleev. Both chemists produced remarkably similar results at the same time working independently of one another. Meyer's 1864 textbook included a rather abbreviated version of a periodic table used to classify the elements. This consisted of about half of...