Atomic theory is a scientific concept that explains how matter is made up of atoms. Its roots can be traced back to the ancient philosophical tradition known as atomism. In a nutshell, atomic theory states that all matter is made up of atoms, and they are made up of various types of matter. Here are a few examples of atomic theory and its predictions. And while the term atomic theory is often confusing, we've outlined the most important concepts you need to understand.
Rutherford's Nuclear Model
Ernest Rutherford was a New Zealand-born physicist who developed the Rutherford model to describe the atom. The experiment that he directed, the Geiger-Marsden experiment, suggested that the plum-pudding model of the atom was incorrect. Rutherford's nuclear model explains how the atom is composed of hydrogen, oxygen, and carbon atoms. In 1909, Rutherford's model was proven correct.
While working at the University of Manchester, Rutherford studied the scattering of alpha particles from gold targets. He noted that the particles scattered at small angles. He noticed that a sharp picture was formed when some particles were accelerated, while others had blurred edges. He subsequently devised a model that would predict the number of accelerated hydrogen atoms. Rutherford's nuclear model would go on to win the Nobel Prize in Chemistry in 1911.
Dalton's Law of Multiple Proportions
The earliest example of Dalton's law of multiple proportions was in the field of reaction stoichiometry. While not exactly the same as the law of multiple compositions, the two are related. The difference is that the latter focuses on the elemental composition of a compound. Because atoms are discrete, they can be understood easily. Therefore, it was Dalton who came up with this idea.
The law of multiple proportions is a fundamental chemical law, which has contributed greatly to the understanding of stoichiometry since its introduction. It was first proposed by English chemist John Dalton in 1803 (who also discovered the law of partial pressures). Although it came after Proust's law of definite proportions, it has a place in atomic theory.
In 1913, Niels Bohr proposed a new model for atomic theory. The Rutherford-Bohr model involved a small, dense nucleus surrounded by orbiting electrons. This model is similar to the structure of the solar system and the attraction between the electrons is provided by electrostatic forces. Today, atomic theory has become a standard part of science education.
The Bohr model, based on the quantum theory of radiation, explained the existence of atomic spectra and a range of definite energies. However, this model had many limitations and was eventually replaced by the Thomson model. This was followed by Rutherford's nuclear atom theory. In the twentieth century, this model has been revised many times. Although it is considered an outdated scientific theory, it is still taught to students to explain energy level diagrams and quantum mechanics.
Bohr's Prediction of Multielectron Atoms
Earlier, a team of chemists predicted that an atom could have more than one electron. Bohr's prediction was rejected. However, his work was corrected by Walther Kossel, a fellow scientist who coined the term "shells". In his prediction, the number of electrons per shell would be limited to eight. However, his model was not accepted by all chemists, who regarded it as a mistake.
In the early 1920s, Bohr's model was regarded as a dead end because it failed to explain spectral lines and the Zeeman effect. Although the model correctly explained the spectral lines of the hydrogen atom, it did not explain the spectral lines of multielectron atoms. In addition, it failed to explain the Stark effect, a phenomenon in which a spectral line splits into fine lines when placed in an electric field. This resulted in a number of discrepancies between Bohr's prediction and the observable world.