History of the Periodic Table
Habish Ribin Haneef
The periodic table is an important part of the world of Chemistry. It is also known as the periodic table of elements and is a tabular display of chemical elements. In the periodic table, elements are arranged on the basis of atomic number. Elements with similar chemical properties comes under the same vertical column. The vertical columns are known as groups and the horizontal rows are known as periods. These are some of the crucial facts we know about the modern periodic table. But have you ever wondered how the periodic table that we know at present has been constructed? There is a long history behind the discovery and development of the modern periodic table. In this blog, let’s discuss the history of the periodic table briefly.
Antoine Lavoisier:
The development of the periodic table started way back in 1789 and Antoine Lavoisier, a French chemist started the proceedings. Lavoisier classified the known elements of that time into four groups. His classification was based on the chemical properties of elements such as gases, non-metals, metals, and earth. According to Lavoisier, an element represents the final stage of chemical decomposition. But, Lavoisier’s attempt was not successful because it contained much wrong information. Lavoisier’s classification included heat, light and a few compounds that were not able to decompose into elements like lime, silica, alumina, barita, and magnesia.
Johann Wolfgang Dobereiner:
The next development in periodic table occurred in the year 1829. In 1829, German chemist Johann Wolfgang Dobereiner classified the elements into triads. Dobereiner triads are defined as, any of several sets of three chemically same elements with the atomic weight of one, which is nearly equal to the mean of the atomic weights of the other two elements. In Dobereiner’s classification, each triad consisted of three elements with similar chemical properties. Each triad had a middle element whose relative atomic mass was approximately the average of the other two elements. But, Dobereiner’s attempt was also unsuccessful because it was only applicable for a few elements. Even though the classification of Dobereiner was a failure, his triad law helped scientists to realise that there was a relationship between the properties and the atomic masses of the elements.
John Alexander Newlands:
After the failure of Dobereiner’s triad, English chemist John Alexander Newlands developed the law of octaves in 1865. Using the 62 elements known at that time, Newlands arranged them in ascending order based on their atomic masses. As a result of this, he observed that every 8th element had similar properties. Based on this observation, Newland’s law of octaves was developed. The law of octaves states that every 8th element has similar properties when the elements are arranged in the increasing order of their atomic masses. This pattern was similar to an octave of notes in music. But, Newland’s attempt was also not successful because the law of octaves was followed by the first 17 elements (from Hydrogen to Calcium) only. Nevertheless, Newlands was the first chemist to demonstrate that elemental properties follow a periodic pattern. This idea was used in the further development process of the periodic table.
Lothar Meyer:
The next contribution in the development of periodic table was given by Lothar Meyer, a German chemist. In 1870, Meyer plotted a graph between atomic volume and atomic mass for all the known elements of that time and obtained various curves. From the curve, Meyer noticed that the elements with the same physical and chemical properties occupied the same positions on the curve. The alkali metals, Li, Na, K, Rb, and Cs that are located at the peaks of the curve have similar chemical properties. Similarly, the halogens, F, Cl, Br, and I that are located at the slopes of the curve too have similar chemical properties. According to the periodicity of properties such as atomic volume, Meyer developed a periodic table of 56 elements in ascending order of atomic masses. Hence, Lothar Meyer was successful in showing the periodic trends in periodic properties.
Dmitri Mendeleev:
Dmitri Mendeleev’s findings was the turning point in the development of the periodic table. Mendeleev, a Russian chemistry professor followed the same pattern of Newlands but made a few changes. Mendeleev formulated a law that states “the properties of an element are the periodic function of their atomic masses.” He arranged elements in periods (horizontal rows) and groups (vertical columns) in the increasing order of atomic weights. There were gaps left in Mendeleev’s periodic table and these gaps were introduced for the undiscovered elements at that time. Mendeleev utilized the positions of the elements in the periodic table to predict the properties of undiscovered elements at that time. He predicted the existence of four new elements which he named eka-aluminium, eka-silicon, eka-boron, and eka-manganese. Fifteen years later, elements like gallium, scandium, and germanium were found and the properties of these elements were similar to that of the elements predicted by Mendeleev. For example, germanium showed the same properties shown by eka-silicon and hence Mendeleev’s predictions become correct. Mendeleev mutually exchanged the positions of nickel (atomic mass= 58.7) with cobalt (atomic mass= 58.9) and iodine (atomic mass= 126.9) with tellurium (atomic mass= 127.6) so that the elements with similar chemical properties were kept under the same group. He also arranged some elements like cobalt, iron, manganese, copper, nickel, etc. in separate groups and these group of elements were known as transition elements. Compared to other scientists, Mendeleev was more successful and it was his findings that became very imperative in the development of modern periodic table.
H.J.G Moseley:
It was Mendeleev’s findings which became very crucial in the development of modern periodic table. But, at the business end, Moseley, an English physicist gave some contributions that led to some modifications in Mendeleev’s periodic table and as a result the modern periodic table was formed. In 1914, Moseley conducted an experiment to measure the frequency of X-ray released from different elements when these elements were bombarded by high energy electrons. As a result, Moseley plotted a graph of the square root of the frequency of x-ray emitted from the elements versus their proton numbers. He obtained a straight line as the output. From this, he concluded that proton numbers should be used as the basis for the periodic change in the chemical properties of elements. Moseley developed a periodic table which was almost similar to that of Mendeleev’s. He arranged the elements in ascending order of their proton numbers. In modern periodic table, the elements are arranged in ascending order of their proton numbers and Moseley holds a key in the invention of the modern periodic table.moseley
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Check your knowledge
Answer. Dobereiner triads are defined as, any of several sets of three chemically same elements with the atomic weight of one, which is nearly equal to the mean of the atomic weights of the other two elements.
Answer. The law of octaves states that every 8th element has similar properties when the elements are arranged in the increasing order of their atomic masses.
Answer. eka-aluminium, eka-silicon, eka-boron, and eka-manganese