Question

Name the scientist who discovered atomic theory of matter.

Answer 1

Hint: Atomic theory is a scientific theory which states that matter is composed of tiny, indivisible particles, which are not visible to our naked eyes. These particles are called atoms.

Complete step by step solution:
John Dalton was the scientist who proposed atomic theory. Atomic theory was discovered in the year 1803. He was born on 6 September 1766 in Eaglesfield, Cumberland. He is a British chemist. He was very well-known for introducing Atomic theory in Chemistry.
Dalton claimed many things in his theory. They were
- He said that all matters are made up of tiny, indivisible and indestructible particles. These particles are called atoms.
- Atoms are tiny particles which can take part in chemical reaction. All the atoms present in an element are identical in mass and properties, but these atoms are different from atoms of other elements.
- Matter can neither be created nor be destroyed. They can be transformed from one form to another.
- Atoms of different elements combine with each other in a simple whole number ratio.
- Atoms of simple elements can combine in more than one ratio to form one or more compounds.
Drawbacks of Dalton theory were
- Dalton in his theory said that atoms are indivisible, but it was later contradicted. It was found that atoms can be divided into subatomic particles.
- It was found that atoms are composed of protons, neutrons, electrons and other subatomic particles.
- He said that atoms of the same element are similar in all aspects, this was later proved wrong. Atoms of the same elements can vary in masses. Such atoms varying in mass are called isotopes.
- He also said that atoms of different elements combine in simple whole number ratios to form compounds. But this is not seen in complex organic compounds like sugar with molecular formula \[{{C}_{12}}{{H}_{22}}{{O}_{11}}\].
- He failed to explain about the presence of allotropes. For example, Carbon elements have allotropes such as graphite and diamond.

Additional information:
Dalton proposed Atomic theory using the following laws.
- Law of constant composition:
This law states that the sample of a pure substance always contains the same elements in the same mass proportions.
- Law of multiple proportions:
This law states that when two elements combine with each other to form more than one compound, the weight of one element that combines with a fixed weight of the other element are in a ratio of small whole numbers.
 - Law of conservation of Mass:
This law states that mass can neither be created nor destroyed by chemical reaction or physical transformation.

Note: - Avogadro in his principle, corrected the flaws in Dalton's theory.
- In his principle he stated that equal volumes of all gases, at the same temperature and pressure, have the same number of molecules.