Chemistry: Periodic Table

 

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What is the periodic table?

A periodic table can be defined as a tabular representation of various elements based on their physical and chemical properties. The periodic table provides a lot of information about the elements. It provides mass number, atomic number, atomic weight, validity, electronegativity, electron gain thalapi, ionic radius, different trends follow it, similarities and differences with other elements, and more. It also represents the representation of metals, non-metals, isotopic, radioactive elements, etc. The classification of elements in this tabular form has made the study of elements much easier.

History of periodic table

Only 31 elements were known in 1800. By 1865 the number of elements reached 63. Currently 118 elements are known. Some of the recently discovered elements are man-made.

Johann Döberiner, a German chemist, was the first to consider the idea of ​​trends among the properties of an element in the early 1800s. He noted the similarity between the physical and chemical properties of various elements in a group of 3 elements, called triads. Thus he made the law of three, What has been said The element at the middle of each triplet had an atomic weight which was approximately half the atomic weight of the other two members ”.

Table – Dobereiner Triads

The next attempt to classify the elements was made in 1862 by a French geologist, ABE de Chancourtis. They arranged the then known elements in order of their increasing atomic weight. He created a cylindrical table of elements to display periodic repetition of properties. But it did not attract much attention.

Then in 1865, John Alexander Newlands established the Law of Octaves. He arranged the elements in increasing order of their atomic weights and found that every eighth element had the same properties as the first element. The relationship was the same as every eighth note in the music’s octave. But Newland’s law seemed to hold true for calcium. But in 1887 she gets Davy medal From Royal community, London.

Table – Octaves of Newland

The modern periodic table gives the main credit for its development to the Russian chemist Dmitry Mendeleev (1834–1907) and the German chemist Lothar Meyer (1830–1895). Working independently, the two chemists proposed in 1869 that if elements were arranged on an increasing order of their atomic weights, then at regular intervals the physical and chemical properties showed similarity. And Mendeleev published a periodic law stating that – “The properties of elements are periodic functions of their atomic weights.”

Table – Mendeleev’s Periodic Table Dmitry Mendeleev

Modern periodic table

And finally, the modern periodic table, as we know it today, was proposed by Henry Mosley in 1913. According to this periodic table, arrangements were made on the basis of increasing order of atomic number of elements. It consists of horizontal lines called periods and vertical columns called groups or families. Groups range from 1–18 and periods 1–7. The table is divided into 4 blocks of elements known as s, p, d, f elements.

Modern periodic table
Henry Moseley

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