Around 1897, scientists gradually determined the basic characteristics of electrons and established that electrons are the same components of various atoms. Usually, atoms are electrically neutral. Since all atoms have negatively charged electrons, there must be positively charged substances among them. At the beginning of the 20th century, two different hypotheses were put forward.
In 1904, Thomson proposed that the positive charges in atoms are distributed in a sphere with uniform volume density, while the negatively charged electrons are distributed in different positions of the sphere, which vibrate at a certain frequency respectively, thus emitting electromagnetic radiation. This model was vividly compared to the "nut bread" model, but the model theory contradicted the experimental results and was soon abandoned.
In 19 1 1, Rutherford proposed that the center of an atom is a positively charged heavy nucleus, which is very small compared with the size of the whole atom. Electrons revolve around the nucleus, similar to planets revolving around the sun. This model is called the nuclear model of atoms, also known as the planetary model. The conclusions drawn from this model are in good agreement with the experimental results and are quickly recognized.
According to the classical electromagnetic theory, electrons should automatically radiate energy, so that the energy of atoms gradually decreases and the frequency of radiation gradually changes, so the emission spectrum should be continuous. Due to the decrease of energy, electrons gradually approach the nucleus along the spiral and finally fall on the nucleus, so the atom should be an unstable system.
But in fact, atoms are stable, and the spectrum emitted by atoms is linear, not continuous. These facts show that the classical electrodynamics established from the study of macroscopic phenomena is not applicable to the microscopic processes in atoms. This requires further analysis of atomic phenomena, exploration of the regularity of internal movement of atoms, and establishment of atomic theory suitable for microscopic processes.
19 13 years, Danish physicist Bohr proposed that the energy possessed by an atom forms discontinuous energy levels on the basis of the nuclear model proposed by Rutherford, combined with the empirical law of atomic spectrum and applied the quantum hypothesis proposed by Planck in 1900 and the photon hypothesis proposed by Einstein in 1905. When the energy levels jump, atoms will