HISTORY OF PERIODIC TABLE

Most of us are familiar with the work done by Mendeleev and Moseley in the development of the periodic table. But there are some other genius minds who contributed towards a logical arrangement of elements.

Antoine Lavoisier

The very first classification of elements came from Lavoisier as early as 1789. This grouping was generally a broad categorization based on the properties of elements. As a result elements were grouped as metals, non-metals, gases, and earths. This classification paved way for further attempts in the coming decades.

Johann Dobereiner

Dobereiner studied the chemical properties of elements in 1829 and found that the elements could be arranged in groups of three (triads) later known as the “Dobereiner’s triads”. Based on such studies lithium, sodium and potassium formed a group. The most interesting part of this classification was that the properties of the middle element in the triad could be predicted from the properties of the first and third element.

Alexandre-Emile Beguyer de Chancourtois

Chancourtois, a French geologist published his findings in 1862. Interestingly this was an attempt of classification of elements by a geologist. He proposed a “vis tellurique” (telluric screw) and arranged the elements in a three dimensional fashion. His arrangement was based on atomic weights of elements.

Tellurium was at the center of the screw in which elements were plotted on the outside of a cylinder in such as way that one complete turn meant an increase in atomic weight by 16, the atomic weight of oxygen. Elements with similar properties were thus found vertically in the diagram that was published in his paper.

John Newlands

Newlands, a British chemist arranged elements by their atomic weights in groups of 7, such that the eight element had similar properties with the first one. The arrangement was much like the octaves of music, thus known as the Newlands’ octaves. The noble gases were not discovered at that time and that is why the elements were grouped in 7 not 8. The drawback in this arrangement was that Newlands did not leave space for the undiscovered elements and that was the reason why the Chemical Society was reluctant to publish the findings. It was much later in 1998 that his recommendations were recognized and commemorative plague was placed on the wall of this birthplace.

Julius Lothan Meyer

Meyer was a German scientist who made several attempts to arrange elements periodically between 1860-1870. Initially he produced a table with 28 elements organized according to their valency and later incorporated transition metals. The arrangement was again according to atomic weights and he found that elements with similar properties were arranged in vertical lines in a graph that he proposed. Meyer was the first to recognize the periodic trends in elements. His graph plotted atomic volume against the atomic weights of elements.

Dmitri Mendeleev

Mendeleev was the first scientist to produce a periodic table in 1869. His table was also based on the atomic weights of elements. By doing so he found that elements with similar properties occurred regularly in the table. The best thing that Mendeleev did was to place the elements against the trend followed by atomic weights if the properties did not match. So he had to change the order. For instance iodine came first in the series to tellurium according to atomic weight, but he found that iodine was very much similar to other halogens, so he had to change the order and place iodine with halogens and tellurium with oxygen and sulphur group. Another important thing in his table was that the left spaces for the undiscovered elements. For example gallium was not discovered at that time, so he left space for it and called it “Eka-aluminum” as it fell after aluminum in the table. Later when gallium was discovered, its properties matched the predictions of Mendeleev. Later on, with the discovery of noble gases, Mendeleev’s predictions were proven and the elements got the periodicity of 8 rather than 7.

Mendeleevium was the name given to element 101 in recognition of his contribution to the field. But he was unfortunate not to receive the Nobel prize for his work.

Henry Moseley

Moseley was the final name in the list of contributors who put the final bricks in the wall to complete the table and the puzzle was finally solved. Moseley’s focus was on the atomic numbers of the elements and it did fit the earlier arrangements based on atomic weights. He used X-rays to determine the atomic numbers of elements. Moseley revealed his work in 1913 and was killed in 1915 in the first world war.

Moseley somewhat confirmed the placement of elements in Mendeleev’s table, for example cobalt and nickel were assigned the atomic numbers 27 and 28 respectively, having nearly similar atomic weights. Later on Moseley confirmed the atomic numbers from the X-ray experiments and were proven correct.  

PC: www.sciencenotes.org, www.wikipedia.org