The Periodic Table

Anoushrayan Deysarkar

The periodic table is a common sight in nearly every chemistry classroom in the world today. But how did it come to be?

In 1789, Antoine Lavoisier published a list of 33 chemical elements, grouping them into gases, metals, nonmetals, and earths.

 In 1829, Johann Wolfgang Döbereiner observed that many elements could be grouped into triads based on their chemical properties. For example, Lithium, Sodium and Potassium were grouped together in a triad, as soft, reactive metals. German chemist Leopold Gmelin worked with this system, and by 1843 he had identified 10 triads, three groups of 4 and 1 group of 5. However, although various chemists were able to identify relationships between small groups of elements, they had yet to build one scheme that encompassed them all.

In 1862, the French geologist Alexandre-Émile Béguyer de Chancourtois published an early form of the periodic table, which he called the telluric helix or screw. His paper used geological rather than chemical terms and did not include a diagram. As a result, it received little attention until the work of Dmitri Mendeleev.

In 1864, Julius Lothar Meyer, a German chemist, published a table with 28 elements. Realizing that an arrangement according to atomic weight did not exactly fit the observed periodicity in chemical properties he gave valency priority over minor differences in atomic weight.

Concurrently, English chemist William Odling published an arrangement of 57 elements, ordered on the basis of their atomic weights. Odling alluded to the idea of a periodic law but did not pursue it. He subsequently proposed (in 1870) a valence-based classification of the elements.

English chemist John Newlands produced a series of papers from 1863 to 1866 noting that when the elements were listed in order of increasing atomic weight, similar physical and chemical properties recurred at intervals of eight. He likened such periodicity to the octaves of music. This so termed Law of Octaves was ridiculed by Newlands’ contemporaries, and the Chemical Society refused to publish his work. The Chemical Society only acknowledged the significance of his discoveries five years after they credited Mendeleev.

Russian chemistry professor Dmitri Mendeleev and German chemist Julius Lothar Meyer independently published their periodic tables in 1869 and 1870, respectively. The recognition and acceptance afforded to Mendeleev’s table came from two decisions he made. The first was to leave gaps in the table when it seemed that the corresponding element had not yet been discovered. Mendeleev was not the first chemist to do so, but he was the first to be recognized as using the trends in his periodic table to predict the properties of those missing elements, such as gallium and germanium. The second decision was to occasionally ignore the order suggested by the atomic weights and switch adjacent elements, such as tellurium and iodine, to better classify them into chemical families.

In 1871, Mendeleev published his periodic table in a new form, with groups of similar elements arranged in columns rather than in rows, and those columns numbered I to VIII corresponding with the element’s oxidation state. He also gave detailed predictions for the properties of elements he had earlier noted were missing but should exist. These gaps were subsequently filled as chemists discovered additional naturally occurring elements.

The popular periodic table layout, also known as the common or standard form is attributable to Horace Groves Deming (1923).

In 1945, Glenn Seaborg, an American scientist, made the suggestion that the actinide elements, like the lanthanides, were filling an f sub-level. Before this time, the actinides were thought to be forming a fourth d-block row. Seaborg’s suggestion was found to be correct, and he subsequently went on to win the 1951 Nobel Prize in chemistry for his work in synthesizing actinide elements. As we know, the periodic table has undergone many changes throughout its history, until it has reached the modern form we see today. Many elements were found in nature, and some have been synthesized in labs. Scientists are working, even now, to find more elements and improve the periodic table. Let us hope that we continue to find out more about the periodic table, and that our chemical knowledge improves in the process.



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