How Many Elements are There in Mendeleev Periodic Table

Introduction

There were known to be 63 elements in the Mendeleev periodic table. Dmitri Ivanovich Mendeleev was a Russian chemist who was a very important contributor to the early development of the periodic table. Mendeleev’s periodic table came into the picture after the rejection of Newlands Octaves. In his periodic table, the elements were arranged on the basis of their atomic masses and chemical and fundamental properties.

Elements in Mendeleev's Periodic Table

Unlike the 118 elements known to us today, there were only 63 elements discovered during Mendeleev’s time. Through his research, Mendeleev found that the properties of the elements he was studying were related to atomic mass in a periodic way. He made the periodic table and arranged the elements such that the elements with similar properties fell into the same vertical columns of the table.

For the chemical properties of the elements, Mendeleev treated the formulae of hydrides and oxides as one of the basic criteria of categorisation. To find a way to categorise the elements known to him, he took 63 cards and wrote the properties of one element on each card. He then selected the elements with similar properties and pinned them on a wall. In this arrangement, Mendeleev noticed that he had managed to arrange the elements in the increasing order of their atomic mass and there was a periodic occurrence of elements with similar properties. He named the vertical columns in his periodic table as groups and the horizontal rows were called the periods.

Since Mendeleev was only familiar with 63 elements, he knew that there would be more elements discovered in the future and so he left some gaps in his table. This allowed new elements to be added to his table without disturbing the existing groups.

However, there were some issues with his table. Mendeleev could not locate Hydrogen in his periodic table. The increase in the atomic mass of elements was not regular and the table could not accommodate isotopes of elements.

Conclusion

Mendeleev’s periodic table consisted of 63 elements that were known to him during his time. He made his periodic table by arranging the elements such that the elements with similar properties were placed in the same vertical columns of the table. He placed cards with information about the properties of the elements on a wall to help him categorising the elements into the table.