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explain dalton's atomic theory and write its drawbacks

Dalton’s atomic theory consists of following postulates:

(i) Matter is made up of very small particles called atoms.

(ii) Atoms can neither be created nor destroyed.

(iii) Atoms of similar substances are similar in all respects (mass, shape and properties)

(iv) Atoms of different substances are different in all respects(mass, shape and properties)

(iv) Atoms of elements combine in the ratio of whole numbers to produce a large number of compound-atoms of a new substance.

Limitations of Dalton’s atomic theory

Dalton’s atomic theory suffered from the following drawbacks:

(i) It failed to explain how and why atoms of different elements combine together to form a new ‘group of atoms’.

(ii) It failed to explain how atoms of different elements differ from each other i.e the structure of atom was unknown.

(iii) It failed to explain the nature of the binding forces between different atoms in a molecule.

(iv) According to Dalton, an atom is indivisible, whereas, it can be divided into sub- atomic particles- electrons, protons and neutrons.

(v) Atoms of the same element can differ from each other.Example – isotopes (atoms of the same element with different masses)

(vi) Atoms of different elements can have same masses (isobars).

 

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DALTON'S ATOMIC THEORY

The theory that all matter is made up of very tiny indivisible partivles (atoms) is called atomic theory of matter. Dalton put forward hi atomic theory of matter in 1808. The various postulates (or assumptions) of Dalton's atomic theory of matter are as follows : 

1. All the matter is made up of very small particles called atoms.

2. Atoms cannot be divided.

3. Atoms can neither ce created nor be destroyed.

4. Atoms are of various kinds. There are as many kinds of atoms as are elements.

5. All the atoms of a given element are identical in every respect, having the same mass, size and chemicla properties.

6. Atoms of different element differ in mass, size and chemical properties.

7. Chemical combination between two (or more) elements consists in the joining together of atoms of these elements to form molecules of compounds.


DRAWBACKS OF DALTON'S ATOMIC THEORY

It is known that some of the statements of Dalton's atomic theory of matter are not exactly correct. Some of the drawbacks of the Dalton's atomic theory of matter are given below : 

1. One of the major drawbacks of Dalton's atomic theory of matter is that atoms were thought to be indivisible. But we know that under special circumstances, atoms can be further divided into electrons, protons and neutrons. So, the atoms are themselves made up of three particles : electrons, protons and neutrons.

2. Dalton's atomic theory says that all the atoms of an element have exactly the same mass. It is however, now known that atoms of the same element can have slightly different masses. Ex - isotopes.

3. Dalton's atomic  theory said that atoms of different elements have different masses. It is however now known that even atoms of different elements can have the same mass. Ex - Isobars.

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