The development of the new atomic model can be attributed to several key scientific discoveries and experiments conducted by different scientists over time. The major contributors to the new atomic model are:
J.J. Thomson's Discovery of Electrons: In the late 19th century, J.J. Thomson conducted experiments with cathode rays and discovered that they were composed of negatively charged particles called electrons. This led to the realization that atoms must contain smaller subatomic particles.
Ernest Rutherford's Gold Foil Experiment: In 1911, Ernest Rutherford performed the famous gold foil experiment. He directed alpha particles at a thin sheet of gold foil and observed their scattering patterns. Rutherford concluded that most of the atom's mass and positive charge were concentrated in a small, dense region at the center called the nucleus. This discovery led to the concept of the atomic nucleus and the understanding that atoms are mostly empty space.
Niels Bohr's Quantum Theory of the Atom: In 1913, Niels Bohr expanded on Rutherford's model and proposed his quantum theory of the atom. He suggested that electrons exist in discrete energy levels or shells around the nucleus and that electrons can transition between these energy levels by absorbing or emitting specific amounts of energy. This model explained the stability of atoms and the observed spectral lines in atomic spectra.
James Chadwick's Discovery of Neutrons: In 1932, James Chadwick confirmed the existence of neutrons, which are neutral subatomic particles with a mass similar to protons. The discovery of neutrons provided a better understanding of atomic mass and the stability of atomic nuclei.
These combined discoveries and experiments gradually led to the development of the new atomic model, which is often referred to as the "electron cloud" or "quantum mechanical" model. This model incorporates the principles of quantum mechanics to describe the behavior and properties of electrons within an atom. It represents electrons as both particles and waves, occupying specific energy levels and forming electron clouds around the nucleus.