what are the demerits of Dalton atomic theory? what are the given postulate?
Answers
John Dalton was an English chemist, physicist, and meteorologist. He is best known for proposing the atomic theory, popularly known as Dalton’s Atomic Theory , which is given below:-
Postulates
1. All matter consists of indivisible particles called atoms.
2. Atoms of the same element are similar in shape and mass, but differ from the atoms of other elements.
3. Atoms cannot be created or destroyed.
4. Atoms of different elements may combine with each other in a fixed, simple, whole number ratios to form compound atoms.
5. Atoms of same element can combine in more than one ratio to form two or more compounds.
6. The atom is the smallest unit of matter that can take part in a chemical reaction.
Drawbacks of Dalton's atomic theory of matter
• An atom is no more be considered as indivisible and can be further subdivided into protons, neutrons and electrons. However an atom is the smallest particle that takes part in chemical reactions.
• According to Dalton, the atoms of same element are similar in all respects. However, atoms of some elements vary in their masses and densities. These atoms of different masses are called isotopes. For example, carbon has two isotopes with mass numbers 12 and 14.
• Dalton also claimed that atoms of different elements are different in all respects. This has been proven wrong in certain cases as in isobars, which are different in atomic no. But has same mass no. e.g. argon and calcium atoms each have an atomic mass of 40 amu.
• According to Dalton, atoms of different elements combine in simple whole number ratios to form compounds. This is not observed in complex organic compounds like sugar (C12H22O11).
• The theory fails to explain the existence of allotropes; it does not account for differences in properties of charcoal, graphite, diamond.
Merits of Dalton’s atomic theory :-
• It has enabled us to explain the laws of chemical combination, which states that every compound consist elements in definite proportion by weight.
• Dalton was the first person to recognize a workable distinction between the ultimate particle of an element (atom) and that of a compound (molecule).
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Demerits:
1) Atom was not indivisible and sub atomic particles were found.
2) isotope was violation for his rule.
3) Atoms of same element can also form bonds.
Postulates:
1. All matter consists of indivisible particles called atoms.
2. Atoms of the same element are similar in shape and mass, but differ from the atoms of other elements.
3. Atoms cannot be created or destroyed.
4. Atoms of different elements may combine with each other in a fixed, simple, whole number ratios to form compound atoms.
5. Atoms of same element can combine in more than one ratio to form two or more compounds.
6. The atom is the smallest unit of matter that can take part in a chemical reaction.