Answer: The invention of the periodic table
In the history of chemistry, Dimitri Mendeleev was the inventor of the periodic table.
- According to him, elements’ physical and chemical properties are the periodic function of their atomic weight.
- His Mendeleev periodic table was based on atomic weight.
- Noble gases were not discovered; only 63 elements were known then.
- He was the first scientist to clarify the elements systematically that is in horizontal rows and vertical columns.
- Horizontal rows were known as periods, and vertical columns were known as groups.
- There were seven periods and eight groups and Mendeleev’s periodic table.