Question

Who proposed atomic theory?

Answer 1

Hint: An English scientist John Dalton gave atomic theory of matter in 1808. This theory describes the certain features of matter, element and compound in terms of atoms. This theory could explain the law of chemical composition.

Complete answer:
 In 1808, an English scientist John Dalton proposed atomic theory (i.e. Dalton’s atomic theory). This theory describes the several features of atoms which is discussed as follows:
All matter around us is made up of an indivisible substance called atom.
Atoms of element are identical, however compound contain different kind of atoms which is combined in a fixed whole number ratio and vary in both mass and size (i.e. law of conservation of constant composition and law of multiple proportions)
During the chemical reaction, mass can neither be created nor be destroyed (i.e. law of conservation of mass).
Hence, John Dalton proposed atomic theory of matter in 1808.

Additional Information: “Atom” is a Greek word which means indivisible. However, nowadays, we know that atoms consist of subatomic particles which are electron (negatively charged), proton (positively charged) and neutron (no charge). In an atom, the nucleus is present at the center which contains protons and neutrons while electrons are present outside the nucleus. The sum of protons represents the atomic number while the sum of protons and neutrons represents the mass number.

Note:
 It is important to note that John Dalton proposed the atomic theory. Dalton’s atomic theory successfully explains the law of constant composition, law of multiple proportions and law of conservation of mass. The theory forms the basic concepts of chemistry.