What is Dalton's atomic theory?

In 1808, a British school teacher named John Dalton presented the atomic theory of matter for the first time. In this, the atom is considered the basic particle of matter. This is called Dalton's atomic theory.

Definition of Dalton's Atomic Theory

According to Dalton's atomic theory, “Every matter is made up of small particles called atoms and the atom cannot be divided by any physical or chemical method.”

The smallest indivisible particle of matter, which was named atom by the Greek philosophers, was also named atom by Dalton.

                This theory of Dalton was based on the laws of chemical combination.

Key points of Dalton's Theory

The main points of this theory are as follows-

1. Every element is made up of tiny indivisible particles called atoms.
2. All the atoms of an element are similar in size and properties but the atoms of different elements are different.
3. The properties of atoms of different elements are also different.
4. Atoms are indestructible i.e. atoms are neither created nor destroyed in a chemical reaction.
5. Atoms of elements combine back to form combined atoms and in modern words this combined atom is called a molecule.
6. The relative number and type of atoms in the combined atom formed is fixed.

Applications of Dalton's Atomic Theory

1. Dalton's atomic theory presents the fundamental idea of ​​the structure of matter. According to this atom is the smallest unit of matter.
2. Dalton's atomic theory incorporates the concept of the law of chemical composition known until then, such as point (4) representing the conservation of mass and point (5) representing the law of definite proportions.
3. Dalton's atomic theory also explains the law of multiple proportion.
4. This principle also shows the variation in the atoms of different elements.

Limitations of Dalton's Atomic Theory

1. According to Dalton, the smallest unit of formation of elements is the atom while the smallest unit of compound is the compound atom, in fact the concept of the combined atom that Dalton introduced was the molecule.
2. This theory does not explain the Berzelius hypothesis which postulated that the same volume of gases under the same conditions of temperature and pressure have the same number of atoms.
3. This theory does not explain the fact that atoms interact with each other to form molecules.
4. It does not shed any light about the nature of forces of atoms and molecules in the physical states of solid, liquid and gas.

1. It does not explain the presence of isotopes and Gelusak's law of gaseous volumes.
2. This theory also does not explain the fact that atoms of different elements have different mass, size and valency.

Current Status of Dalton's Atomic Theory

1. The discovery of electrons, protons, neutrons and other sub-atomic particles has proved that the atom is not indivisible.
2. After the discovery of isotopes, it has been proved that atoms of the same element can have different atomic masses.
3. After the discovery of isobars, it has been proved that atoms of different elements can have the same mass.
4. With the advent of nuclear chemistry, the transformation of one atom into another has become possible.
5. Atoms can also interact with each other in fractional proportions.

Modern atomism may be different from Dalton's atomic theory, but his contribution to chemistry is of great importance because it was only after giving his theory that electrons, protons, neutrons and other particles were discovered.

The world came to know about many concepts and due to all these reasons Dalton's atomic theory became the theoretical basis of chemistry.

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