Give an account of the process adopted by Mendeleev ′ for the classification of elements. How did he arrive at “Periodic Law”?
Mendeleev organized elements based on their atomic weights and recurring patterns of chemical properties, leading to the formulation of the Periodic Law. He arranged elements in horizontal rows (periods) and vertical columns (groups), with elements having similar properties grouped together. This arrangement revealed a periodic relationship between atomic weight and chemical properties, which Mendeleev formalized as the Periodic Law.
Here’s a more detailed breakdown:
1. The Process:
Studying Properties:
Mendeleev meticulously studied the properties of each known element. He focused on the chemical properties, particularly the compounds formed with hydrogen and oxygen.
Arranging by Atomic Weight:
He arranged elements in order of increasing atomic weight, creating a table-like structure.
Grouping by Similarity:
He noticed that elements with similar properties reappeared periodically, forming groups in the table.
Leaving Gaps:
He left gaps in the table for elements that were yet to be discovered, predicting their properties based on their position and the properties of surrounding elements.
Predicting New Elements:
Mendeleev famously predicted the existence and properties of elements like gallium (Eka-boron), scandium (Eka-zinc), and germanium (Eka-aluminum).
2. Arrival at the Periodic Law:
Pattern Recognition:
By arranging elements in order of atomic weight, Mendeleev observed that the properties of elements recurred periodically.
Formalization:
He formulated the Periodic Law, stating that “the properties of elements are a periodic function of their atomic weights”. This meant that elements with similar properties appeared at regular intervals when arranged by increasing atomic weight.
Foundation for the Periodic Table:
The Periodic Law provided the foundation for organizing elements into the periodic table, which is still used today.