The indivisibility of an atom was proved wrong: an atom 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.

Drawbacks of Dalton's Atomic Theory

Lack of Subatomic Particles:
- One of the main drawbacks of Dalton's atomic theory is that it did not account for the existence of subatomic particles such as protons, neutrons, and electrons.
- Dalton believed that atoms were indivisible and indestructible, and did not consider the possibility of smaller particles within atoms.
- The discovery of subatomic particles and their role in atomic structure challenged Dalton's theory.

Inability to Explain Isotopes and Isobars:
- Dalton's atomic theory was unable to explain the existence of isotopes and isobars.
- Isotopes are atoms of the same element with different numbers of neutrons, while isobars are atoms of different elements with the same mass number.
- Dalton's theory assumed that all atoms of a given element were identical, which contradicts the existence of isotopes and isobars.

Failure to Explain Chemical Reactions:
- Dalton's atomic theory was unable to explain the nature of chemical reactions and the rearrangement of atoms during reactions.
- According to Dalton, atoms combine in fixed ratios to form compounds, but he did not provide an explanation for why this occurs or how atoms rearrange themselves during chemical reactions.
- The discovery of the electron and the development of the electron configuration model later provided a more comprehensive understanding of chemical reactions.

Lack of Explanation for Atomic Masses:
- Dalton's atomic theory did not provide a clear explanation for atomic masses.
- While Dalton proposed that atoms of different elements have different masses, he did not offer an explanation for why atoms of the same element have different masses in the form of isotopes.
- It was later discovered that atomic masses are influenced by the number of protons, neutrons, and electrons in an atom.

Limitation of the Law of Multiple Proportions:
- Dalton's atomic theory relied on the Law of Multiple Proportions, which states that when two elements form more than one compound, the ratio of the masses of the second element that combine with a fixed mass of the first element can be expressed in small whole numbers.
- While this law is generally true, there are exceptions where the ratios of elements in compounds do not follow small whole numbers, which challenges Dalton's theory and the Law of Multiple Proportions.

In conclusion, Dalton's atomic theory was a significant advancement in the understanding of the structure of matter, but it had several drawbacks. The theory failed to account for the existence of subatomic particles, explain isotopes and isobars, provide an explanation for chemical reactions, offer a clear explanation for atomic masses, and had limitations in the Law of Multiple Proportions. Despite these limitations, Dalton's atomic theory laid the foundation for further scientific discoveries and the development of more comprehensive models of atomic structure.