A French chemist Antoine Lavoisier (1743–1794), known as the “Father Of Modern Chemistry” laid the foundation of modern chemistry. Lavoisier accepted the idea of an element as any material made of only one component. He identified a compound as any material composed of two or more elements. Hydrogen, for example, is an element because it is made up of hydrogen atoms only and water is a compound because it is made of atoms of the elements hydrogen and oxygen.

Lavoisier measured the mass of a sealed glass vessel containing tin and the mass of the same vessel containing a white powder left after the tin underwent a chemical reaction. He found the mass to be the same before and after the reaction.

Law Of Conservation Of Mass:
The law of conservation of mass states that the total mass present before a chemical reaction is the same as the total mass present after the chemical reaction, thus, mass is conserved. Law of conservation of mass is observed in the given example, because mass of reactants before the reaction is same as the mass of the products after the reaction.

Law Of Multiple Proportions:
The law of multiple proportions is one of the fundamental laws of stoichiometry and was first discovered by the English chemist John Dalton in 1803. The law states that when chemical elements combine, they do so in a ratio of small whole numbers. For example, carbon and oxygen react to form carbon monoxide (CO) or carbon dioxide (CO₂), but not CO_1.5. Further, it states that if two elements form more than one compound between them, the ratios of the masses of the second element to a mass of the first element will also be in small whole numbers.

Law Of Definite Compositions:
“The Law of Definite Composition states: A compound always contains two or more elements combined in a definite proportion by mass”. For example the chemical definition of water is H₂O. There are always 2 atoms of hydrogen to one of oxygen in our definition of water. Or, 8g of Oxygen for every gram of Hydrogen.

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