Limitations of J.J. Thomson’s model of the atom:

1. Lack of explanation for stability:
Thomson's model, also known as the "plum pudding" model, proposed that atoms consisted of a positively charged sphere with negatively charged electrons embedded within it. However, this model did not provide an explanation for the stability of the atom. According to classical physics, the negatively charged electrons should have been attracted to the positively charged sphere and eventually collapsed into it, resulting in an unstable atom.

2. Absence of a nucleus:
Thomson's model did not incorporate the concept of a nucleus. Subsequent experiments by Ernest Rutherford and his colleagues demonstrated that the atom has a tiny, dense, and positively charged nucleus at its center. In Thomson's model, the positive charge was spread uniformly throughout the atom, which did not align with the later discovery of the nucleus.

3. Failure to explain the emission spectrum:
Thomson's model could not explain the observed emission spectra of elements. The emission spectrum of an element consists of discrete lines of specific frequencies, which are characteristic of the element. However, the plum pudding model could not account for the existence of discrete energy levels within the atom that would produce such specific frequencies.

4. Inability to explain alpha particle scattering experiments:
Rutherford's alpha particle scattering experiments disproved Thomson's model. The experiments showed that a significant portion of the alpha particles passed straight through the atom, indicating that most of the atom is empty space. This observation contradicted the plum pudding model, which suggested that the positive charge was spread uniformly throughout the atom.

5. Ignorance of subatomic particles:
Thomson's model did not account for the existence of subatomic particles other than electrons. Later discoveries, such as the existence of protons and neutrons, challenged the simplicity of Thomson's model and led to the development of more accurate atomic models.

6. Lack of explanation for atomic mass:
Thomson's model did not provide an explanation for the atomic mass of elements. It could not account for the fact that different elements have different atomic masses, as it did not consider the existence of protons and neutrons, which contribute to the atomic mass.

7. Failure to explain the stability of isotopes:
Thomson's model could not explain the stability of isotopes, which are atoms of the same element with different numbers of neutrons. The model did not account for the presence of neutrons, which play a crucial role in determining the stability and properties of isotopes.