(a) Dimitri Mendeleev
He formulated the – Periodic Table of elements.
1. He systematically arranged the dozens of known element by atomic weights and could even predict the properties of the still unknown elements.
2. He devised the Periodic Table. He was best known for his discovery of the – Periodic Law.
(b) Antoine Lavoisier
1. He recognised and named oxygen in 1778 & later – hydrogen in 1783.
2. He also wrote the first extensive list of elements and helped to reform chemical nomenclature.
3. In 1774, he turned his attention to the phenomenon of combustion with his famous experiment, in which he heated pure mercury in a swan necked retort, leading to the discovery of oxygen.
(c) John Dalton
1. He compiled his theory in 1803 known as Dalton’s atomic theory.
2. The main postulates of Dalton’s atomic theory are that “Matter consists of particles called atoms, which are indivisible and cannot be created or destroyed.”
3. The theory was later contradicted in certain aspects by the Modem atomic theory.