Mendeleev's Periodic Table

Till now about 118 elements are found in nature. About 150 years ago new elements were found day to

day and their physical and chemical properties were different. To study their properties it was going to be nuisance task. So scientists started classifying them according to their physical and chemical properties. They formed a table by classification of elements which is known as periodic table.
Mendeleev’s periodic Table:  The first periodic table was published by Russian chemist  Dmitri Mendeleev in 1869. It was published under Mendeleev’s periodic law which states that “ The physical and chemical properties of elements are periodic function of their atomic weight”. Which explains that after certain number of elements, going on increase of atomic weight, similar element repeats(with similar properties). The elements on horizontal row were called period and elements on vertical column were called group.

Importance of Mendeleev’s periodic table:

• It was the first event to study elements by classification
• Space was provided to the elements which were not discovered
• It made easy to do correction of atomic weight of several elements like gold, platinum, uranium etc.

Drawbacks of Mendeleev’s periodic table:

• Hydrogen was placed in group I with alkali metal though it was a non metal.
• Highly reactive alkali metals like Lithium(Li), Sodium(Na) and potassium(K) were placed with less reactive metals like copper, silver and gold.
• Cobalt was placed before Nickel though atomic weight of  Ni was less than that of Co.