Preodic Table - 4

Historical Review of the Preodic Table

Introduction

The Preodic Table is a very familiar instrument in our lives, and is part of the didactic material for any student of chemistry, medicine and engineering.

Preodic Table

The Preodic Table no longer has the same organization of elements as before, now they are divided into groups which are the columns, which are 18 groups and each group corresponds to a name that characterizes all members of the same, as are also Divided into periods which are the rows that we observe in the periodic table and which are 7 periods.

Preodic Table’s History.

In 1829 the German chemist Döbereiner made the first attempt to establish an order in the chemical elements, noting in his works the similarities between the elements chlorine, bromine and iodine on the one hand and the regular variation of their properties on the other.

From 1850 to 1865 many new elements were discovered and remarkable progress was made in the determination of the atomic masses, in addition, other properties of the same were better known.

In 1864 Newlands established the law of octaves. Having ordered the elements known by their atomic weight and after arranging them in vertical columns of seven elements each, he observed that in many cases elements with similar properties and that had a regular variation coincided in the horizontal rows.

In 1869 the German chemist Julius Meyer and the Russian chemist Dimitri Mendelyev proposed the first “Periodic Law”.

Meyer, when studying the atomic volumes of the elements and representing them against the atomic weight, observed the appearance on the graph of a series of waves. Each descent from a maximum (which corresponded to an alkali metal) and climbed to the next, represented for Meyer a period.

Using as criterion the valence of the different elements, in addition to its atomic weight, Mendelyev presented his work in the form of a table in which the periods were filled per the valences of the elements.

The table explained the observations of Döbereiner, fulfilled the law of the octaves in its first periods and coincided with that predicted in the chart of Meyer. In addition, observing the existence of gaps in its table, Mendelyev deduced that there should be elements that had not yet been discovered and also advanced the properties that these elements should have according to the position they should occupy in the table.

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