Atomic theory is a physical theory that assumes that everything in the world consists of the smallest particles - atoms , held together by nuclear and electrical forces . In the XX century , it was proved in practice that an atom can be divided into even smaller - subatomic - particles.
Content
History
Atomism
In ancient Greek philosophy , and later in the Middle Ages , people assumed that things around them consist of two parts: indivisible atoms, somehow linked to each other, and from the void between the atoms. Atoms were considered eternal and indestructible corpuscles . [1] [2] This position was reflected in the writings of philosophers such as Democritus and Leucippus , but there was no evidence of this theory at that time.
The first theory of atomic structure
At the end of the 18th century , the chemical conservation laws were discovered:
- The law of conservation of mass , discovered in 1789 by Antoine Laurent Lavoisier , states that the mass of reagents does not change during a chemical reaction; [3]
- The law of constancy of composition , discovered in 1799 by Joseph Louis Proust , states that any particular chemical compound, regardless of the method of its preparation, consists of the same chemical elements; [four]
- The law of multiple relations , discovered in 1803 by John Dalton , states that the ratio of the masses of one element to another will be an integer. [five]
To fulfill these laws, matter must have a discrete structure. But at that time, the structure of what we now call the "molecule" was not entirely clear. In 1811, Amedeo Avogadro conducted a series of experiments with gas and found that two liters of hydrogen react with only one liter of oxygen to produce water vapor. [6] As a result of the study of the Brownian motion discovered in 1827 [7], it became clear that matter consists of separate particles — atoms that can assemble into groups — molecules — that is, an atomic theory of the structure of matter was created.
Discovery of subatomic particles
Until 1897, atoms were considered indivisible. In 1897, Joseph John Thomson conducted an experiment with a fruit pipe , [8] in which the electron was first observed. A certain voltage was applied to the cathode , and, as it later turned out, under such conditions the cathode emits electron beams. Thomson found that these beams are deflected when exposed to an electromagnetic field . Thomson himself called these particles corpuscles , but later they were given a separate name - electrons.
Opening the nucleus of an atom
Thomson's atom model was refuted in 1909 by Thomson's student Ernest Rutherford . The latter found that the atom is not uniform in structure: in the center there is a massive positive dense core , and electrons fly around it, like planets around the Sun.
It turned out that if alpha particles are fired at a thin sheet of gold , then alpha particles will deviate at different angles, and some of them will be angled larger and this can only happen if a massive positive alpha particle encounters a fairly massive positive obstacle in its path. [9]
Creating a quantum theory of the atom
The planetary model had a number of shortcomings, the most significant of which was the theoretically correct loss of electron energy: since the electron rotates around an atom, it is subject to centripetal acceleration , and according to Larmor’s formula, any charged particle moving with acceleration emits. That is, it loses energy. And if the electron loses energy, then in the end it must fall on the nucleus, which in reality does not happen.
In 1913, Niels Bohr suggested that an electron can rotate not in any way, but in strictly defined orbits, without changing its energy for an arbitrarily long time. The transition from orbit to orbit requires a certain energy - a quantum of energy .
Isotope discovery
In 1907, a radio chemist Frederick Soddy discovered that there are substances with the same chemical properties, but differing in the number of neutrons .
Opening Kernel Divisibility
In 1930, it was discovered that while high-energy alpha particles fall on some light elements, the latter emit rays with unusually high penetrating power. This radiation has a much greater penetrating power than all other known rays. In 1932, Irene and Frederic Joliot-Curie showed that if this unknown radiation hits paraffin, then high-energy protons are formed that do not coincide with theoretical calculations. Physicist James Chadwick suggested that this radiation consists of uncharged particles with a mass close to the mass of a proton, and conducted a series of experiments [ what? ] confirming this hypothesis. These uncharged particles were called neutrons.
Discovery of atomic orbitals
In 1924, Louis de Broglie suggested that all particles are connected to a wave, later called de Broglie wave with a frequency and with wavelength
In 1926, the Schrödinger equation was written, [10] describing subatomic particles as waves. A little later, Max Bourne suggested that wave-particle duality is true not only for photons , but in principle for all particles. The concept of orbital was introduced - the place of the most likely location of an electron of a given atom. After all, theoretically, an electron can be very rarely detected at any distance from the atom, [11] but most often it is somewhere near it, just “on the orbital”.
Theory of the structure of the atom in culture
- Quite well known is the statement of R. Feynman :
| If, as a result of some kind of global catastrophe, all accumulated scientific knowledge would be destroyed, and only one phrase would pass to the future generations of living beings, then which statement, made up of the least number of words, would bring the most information? I believe that this is an atomic hypothesis: all bodies are composed of atoms - small bodies that are in continuous motion, are attracted at small distances, but repelled if one of them is denser pressed against the other. This phrase alone contains an incredible amount of information about the world, you just have to attach a little imagination and a little thought to it.R. Feynman . |
- The simplified atom model is one of the famous symbols of science .
Notes
- ↑ Aristotle , Metaphysics I, 4, 985 b 10-15.
- ↑ Berryman, Sylvia, “Ancient Atomism”, The Stanford Encyclopedia of Philosophy (Fall 2008 Edition), Edward N. Zalta (ed.), Http://plato.stanford.edu/archives/fall2008/entries/atomism-ancient/
- ↑ Weisstein, Eric W. Lavoisier, Antoine (1743-1794) ] . scienceworld.wolfram.com. Date of treatment August 1, 2009. Archived on April 7, 2013.
- ↑ Proust, Joseph Louis. " Researches on Copper ", excerpted from Ann. chim. 32, 26-54 (1799) [as translated and reproduced in Henry M. Leicester and Herbert S. Klickstein, A Source Book in Chemistry , 1400-1900 (Cambridge, MA: Harvard, 1952)]. Retrieved on August 29, 2007.
- ↑ Andrew G. van Melsen. From Atomos to Atom. - Mineola, NY: Dover Publications, 1952. - ISBN 0-486-49584-1 .
- ↑ Avogadro, Amedeo. Essay on a Manner of Determining the Relative Masses of the Elementary Molecules of Bodies, and the Proportions in Which They Enter into These Compounds // Journal de Physique : journal. - 1811 .. - Vol. 73 . - P. 58—76 .
- ↑ Einstein, A. Über die von der molekularkinetischen Theorie der Wärme geforderte Bewegung von in ruhenden Flüssigkeiten suspendierten Teilchen (German) // Annalen der Physik : magazin. - 1905. - Bd. 322 , Nr. 8 . - S. 549 . - DOI : 10.1002 / andp.19053220806 . - .
- ↑ Thomson, JJ Cathode rays (Eng.) // Philosophical Magazine : journal. - 1897. - Vol. 44 , no. 269 . - P. 293 . - DOI : 10.1080 / 14786449708621070 .
- ↑ Geiger, H. The Scattering of the α-Particles by Matter // Proceedings of the Royal Society : journal. - 1910. - Vol. A 83 . - P. 492-504 .
- ↑ Schrödinger, Erwin. Quantization as an Eigenvalue Problem (neopr.) // Annalen der Physik . - 1926. - T. 81 , No. 18 . - S. 109-139 . - DOI : 10.1002 / andp.19263861802 . - .
- ↑ Mahanti, Subodh . Max Born: Founder of Lattice Dynamics . Archived January 22, 2009. Date of treatment August 1, 2009.