section_path: Periodic table
section_name: Periodic table
paragraph_text: Periodic table
  
  In 1863, there were 56 known elements with a new element being discovered at a rate of approximately one per year. Other scientists had previously identified periodicity of elements. John Newlands described a Law of Octaves, noting their periodicity according to relative atomic weight in 1864, publishing it in 1865. His proposal identified the potential for new elements such as germanium. The concept was criticized, and his innovation was not recognized by the Society of Chemists until 1887. Another person to propose a periodic table was Lothar Meyer, who published a paper in 1864 describing 28 elements classified by their valence, but with no predictions of new elements.
  
  After becoming a teacher in 1867, Mendeleev wrote Principles of Chemistry (Russian: Основы химии, romanized: Osnovy khimii), which became the definitive textbook of its time. It was published in two volumes between 1868 and 1870, and Mendeleev wrote it as he was preparing a textbook for his course. This is when he made his most important discovery. As he attempted to classify the elements according to their chemical properties, he noticed patterns that led him to postulate his periodic table; he claimed to have envisioned the complete arrangement of the elements in a dream:
  
  I saw in a dream a table where all elements fell into place as required. Awakening, I immediately wrote it down on a piece of paper, only in one place did a correction later seem necessary.
  
  Unaware of the earlier work on periodic tables going on in the 1860s, he made the following table:
  
  By adding additional elements following this pattern, Mendeleev developed his extended version of the periodic table. On 6 March 1869, he made a formal presentation to the Russian Chemical Society, titled The Dependence between the Properties of the Atomic Weights of the Elements, which described elements according to both atomic weight (now called relative atomic mass) and valence. This presentation stated that
  
  Mendeleev published his periodic table of all known elements and predicted several new elements to complete the table in a Russian-language journal. Only a few months after, Meyer published a virtually identical table in a German-language journal. Mendeleev has the distinction of accurately predicting the properties of what he called ekasilicon, ekaaluminium and ekaboron (germanium, gallium and scandium, respectively).
  
  Mendeleev also proposed changes in the properties of some known elements. Prior to his work, uranium was supposed to have valence 3 and atomic weight about 120. Mendeleev realized that these values did not fit in his periodic table, and doubled both to valence 6 and atomic weight 240 (close to the modern value of 238).
  
  For his predicted three elements, he used the prefixes of eka, dvi, and tri (Sanskrit one, two, three) in their naming. Mendeleev questioned some of the currently accepted atomic weights (they could be measured only with a relatively low accuracy at that time), pointing out that they did not correspond to those suggested by his Periodic Law. He noted that tellurium has a higher atomic weight than iodine, but he placed them in the right order, incorrectly predicting that the accepted atomic weights at the time were at fault. He was puzzled about where to put the known lanthanides, and predicted the existence of another row to the table which were the actinides which were some of the heaviest in atomic weight. Some people dismissed Mendeleev for predicting that there would be more elements, but he was proven to be correct when Ga (gallium) and Ge (germanium) were found in 1875 and 1886 respectively, fitting perfectly into the two missing spaces.
  
  By using Sanskrit prefixes to name "missing" elements, Mendeleev may have recorded his debt to the Sanskrit grammarians of ancient India, who had created theories of language based on their discovery of the two-dimensional patterns of speech sounds (exemplified by the Śivasūtras in Pāṇini 's Sanskrit grammar). Mendeleev was a friend and colleague of the Sanskritist Otto von Böhtlingk, who was preparing the second edition of his book on Pāṇini at about this time, and Mendeleev wished to honor Pāṇini with his nomenclature.
  
  The original draft made by Mendeleev would be found years later and published under the name Tentative System of Elements.
  
  Dmitri Mendeleev is often referred to as the Father of the Periodic Table. He called his table or matrix, "the Periodic System".