But the properties of the atom were considered eternal and inexplicable. In this manner the atom appeared as a qualitatively unique particle of matter, characterized by strictly defined physical and chemical properties. It was established that each element had a characteristic optical spectrum spectral analysis was discovered by the German physicists G. In the 19th century the optical, as well as the chemical, properties of atoms were studied. Canizzaro (1858), drew a sharp line between the atom and the molecule. The investigations of the Italian scientists A. Starting from these assumptions Dalton formulated his law of multiple proportions. All chemical reactions are mere regroupings of atoms into new compound particles. Chemical compounds are a collection of “combined atoms” which contain a specific (characteristic for a given complex substance) number of atoms of each element. According to Dalton, the basic characteristic of the atom is its atomic mass.
Dalton was the first (1803) to consider the atom as the smallest particle of a chemical element, distinguished from atoms of other elements by its mass. In the late 18th and early 19th centuries, as a result of the rapid development of chemistry, a basis for the quantitative treatment of the study of atoms was created. The study of atoms still had an abstract, natural-philosophical character. Lomonosov, and certain other scientists supposed that atoms could combine into more complex particles-“corpuscles.” However, specific chemical and physical properties were not attributed to atoms. Combinations of atoms in one or another order produce various substances, and the motions of atoms determine all phenomena that take place in matter. Atoms were considered absolutely indivisible and immutable solid particles whose different types are distinguished by size and form. The concepts of atoms that prevailed in the 17th and 18th centuries were poorly defined. In the 17th century, the ideas were revived by the French philosopher P. Hypothesis concerning the existence of atoms as indivisible particles arose even in antiquity ideas of atomism were first stated by the ancient Greek thinkers Democritus and Epicurus. In the 1950’s the physics of elementary particles-high-energy physics-also developed as an independent branch.Įarly history: Study of atoms in the 17th to 19th centuries.
In the 1930’s it was shown that the interactions which occur in the atomic nucleus were of a nature different from those which occur in the outer shell of the atom, and in the 1940’s nuclear physics branched off into an independent scientific discipline. In the first phase of its development, atomic physics also included problems associated with the structure of the atomic nucleus. In the second decade of the 20th century it was established that the atom consisted of a nucleus and electrons bound together by electrical forces. Atomic physics arose at the turn of the 20th century. The branch of physics in which the structure and states of atoms are studied. The systemization and classification of atomic energy levels (spectroscopy) has played a central role in developing an understanding of atomic structure. The most characteristic signature of these various excited states is the radiation emitted or absorbed when the atom undergoes a transition from one state to another. These are also ordered in accordance with relatively simple hierarchies determined by the laws of quantum mechanics. See Quantum electrodynamics, Quantum mechanicsĮach atomic element, normally found in its ground state (that is, with its electron configuration corresponding to the lowest state of total energy), can also exist in an infinite number of excited states. These include electron affinity, polarizability, angular momentum, multiple electric moments, and magnetism. In addition to their classification by chemical activity and atomic weight, the various elements of this table are characterized by a wide variety of observable properties. These are systematized by the Mendeleev periodic table.
Despite the enormous complexity of most atomic systems, in which each electron interacts with both the nucleus and all the other orbiting electrons, the wavelike nature of particles, combined with the Pauli exclusion principle, results in an amazingly orderly array of atomic properties. These are almost completely determined by the laws of quantum mechanics, with very refined corrections required by quantum electrodynamics. The study of the structure of the atom, its dynamical properties, including energy states, and its interactions with particles and fields.
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