As scientific knowledge advanced, several modifications and refinements were made to John Dalton's original atomic theory. Some of the key modifications and developments include:
Subatomic Particles: Dalton's theory proposed that atoms were indivisible and indestructible. However, the discovery of subatomic particles such as electrons, protons, and neutrons revealed that atoms are composed of smaller components. J.J. Thomson's discovery of the electron and subsequent experiments by Ernest Rutherford and others led to the development of the atomic model with a nucleus containing protons and neutrons, orbited by electrons.
Atomic Structure: Dalton's theory suggested that atoms were solid, indivisible spheres. The subsequent discoveries revealed that atoms have a more complex structure. The Rutherford model proposed a central positively charged nucleus surrounded by negatively charged electrons in specific energy levels or shells.
Isotopes: Dalton's theory assumed that all atoms of an element have the same mass. However, it was later discovered that some elements exist in different forms with the same number of protons but different numbers of neutrons. These different forms are called isotopes. Isotopes have different atomic masses but exhibit similar chemical properties.
Nuclear Reactions: Dalton's theory did not account for nuclear reactions, which involve changes in the nucleus of an atom. The discovery of radioactivity and the understanding of nuclear reactions, such as nuclear fission and fusion, expanded our understanding of atomic and subatomic processes.
Quantum Mechanics: Dalton's theory did not incorporate the principles of quantum mechanics, which explain the behavior of particles at the atomic and subatomic levels. The development of quantum mechanics in the early 20th century provided a more accurate description of atomic structure and the behavior of electrons, incorporating concepts like wave-particle duality and electron orbitals.
These modifications and advancements in atomic theory have led to a more comprehensive and accurate understanding of the nature of atoms and their constituents. The field of atomic and quantum physics continues to evolve, with ongoing research and discoveries shaping our understanding of the microscopic world.