Atomic theory . It is a theory of the nature of matter , which it claims is made up of small particles called atoms. Atomic theory began thousands of years ago as a philosophical concept and it was in the 19th century when it achieved widespread scientific acceptance thanks to discoveries in the stoichiometry field . Chemists at the time believed that the basic units of the elements were also the fundamental particles of nature and called them atoms (from the Greek word atoms , which means “indivisible”) thanks to electromagnetism and radioactivity , physicists discovered that the so-called “indivisible atom” was actually a conglomerate of various subatomic particles (mainly electrons , protons, and neutrons ), which can exist separately. In fact, in certain environments, such as the stars of neutrons , extreme temperature and high pressure prevents the atoms exist as such. The field of science that studies the fundamental particles of matter is called Particle Physics
Summary
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- 1 atomic theory Dalton
- 1 Birth of modern atomic theory
- 1.1 Precedents
- 2 Discovery of subatomic particles
- 3 Discovery of the nucleus
- 4 Discovery of isotopes
- 5 Discovery of the neutron
- 1 Birth of modern atomic theory
- 2 Quantum models of the atom
- 3 Importance
- 4 External links
Dalton’s Atomic Theory
Birth of modern atomic theory
During the eighteenth century and the first years of the nineteenth century , in their quest to know and interpret nature , scientists intensively studied chemical reactions through numerous experiments . These studies made it possible to find very precise relationships between the masses of solid substances or between the volumes of gases involved in chemical reactions. The relationships found are known as laws of chemistry. Among the fundamental laws of chemistry , there are some that establish the relationships between masses, called gravimetric laws andothers that relate volumes, called volumetric laws. John Dalton developed his atomic model, in which he proposed that each chemical element was made up of equal and exclusive atoms, and that although they were indivisible and indestructible, they could associate to form more complex structures (chemical compounds). This theory had several precedents.
Precedents
The first was the law of conservation of mass , formulated by Antoine Lavoisier in 1789 , which states that the total mass in a chemical reaction remains constant. This law suggested to Dalton the idea that matter was indestructible.
The second was the Law of Defined Proportions . Enunciated by the French chemist Joseph Louis Proust in 1799 , it states that, in a compound, the elements that make it up combine in defined proportions of mass and characteristics of the compound.
Dalton studied and expanded Proust’s work to develop the Law of Multiple Proportions : when two elements combine to originate different compounds, given a fixed quantity of one of them, the different quantities of the other combine with said fixed quantity to give as Product compounds, are in relation to simple integers.
The law of Avogadro allowed to deduce the diatomic nature of numerous gases , studying the volumes in which they reacted. For example: the fact that two liters of hydrogen reacted with one liter of oxygen to produce two liters of water vapor (at constant pressure and temperature), meant that a single oxygen molecule divides into two to form two water particles . In this way Avogadro was able to calculate more accurate estimates of the atomic mass of oxygen and other elements, and made the distinction between molecules and atoms.
Discovery of subatomic particles
Until 1897 , atoms were believed to be the smallest division of matter, when JJ Thomson discovered the electron through his experiment with the cathode ray tube . The cathode ray tube Thomson used was a closed glass container, in which the two electrodes were separated by a vacuum. When a voltage difference is applied to the electrodes, cathode rays are generated, which create a phosphorescent glow when they collide with the opposite end of the glass tube. Through experimentation, Thomson discovered that rays were deflected by applying an electric field (in addition to being deflected by magnetic fields, which was already known). He claimed that these rays, rather than waves, were made up of negatively charged particles that he called “corpuscles” (later, other scientists would rename them as electrons).
Core discovery
In their experiment, Hans Geiger and Ernest Marsden bombarded alpha particles through a thin gold foil (which would collide with a fluorescent screen they had placed around the foil). Given the minimum electron mass, the high mass and momentum of alpha particles, and the uniform distribution of positive charge in the Thomson model, these scientists expected all alpha particles to pass through the gold foil without deviation, or by the On the contrary, that they be absorbed. To his amazement, a small fraction of the alpha particles suffered a sharp drift. This induced Rutherfordto propose the planetary model of the atom, wherein the electrons orbiting in space around a large compact nucleus, like planets and sun .
Discovery of isotopes
In 1913 , Thomson channeled a stream of neon ions through magnetic and electrical fields , until it collided with a photographic plate he had placed on the other side. He observed two incandescent zones on the plate, revealing two different deflection paths. Thomson concluded that this was because some of the neon ions had different masses; this is how he discovered the existence of isotopes .
Neutron Discovery
In 1928 Walther Bothe observed that beryllium emitted electrically neutral radiation when bombarded with alpha particles. In 1932 , James Chadwick exposed various elements to this radiation and deduced that it was composed of electrically neutral particles with a mass similar to that of a proton. Chadwick called these particles “neutrons”.
Quantum models of the atom
The planetary model of the atom had its flaws. First, according to the Larmor formula of classical electromagnetism , an accelerating electric charge emits electromagnetic waves, and an orbiting charge would lose energy and describe a spiral until it finally fell into the nucleus. Another phenomenon that the model did not explain was why excited atoms only emit light with certain discrete spectra.
The quantum theory revolutionized physics at the beginning of the century XX , when Max Planck and Albert Einstein postulated that emits or absorbs a slight amount of energy in fixed amounts called quanta. In 1913 , Niels Bohr incorporated this idea into his atomic model , in which electrons could only orbit around the nucleus in certain circular orbits, with a fixed energy and angular momentum, and the distances of the nucleus being proportional to the respective levels of Energy.
In 1924 , Louis de Broglie proposed that all objects, particularly subatomic particles, such as electrons, could have wave properties . Erwin Schrödinger , fascinated by this idea, investigated whether the motion of an electron in an atom could be better explained as a wave than as a particle. The Schrödinger equation, published in 1926, describes the electron as a wave function rather than as a particle, and predicted many of the spectral phenomena that Bohr’s model could not explain.
In 1927 , Werner Heisenberg indicated that since a wave function is determined by time and position, it is impossible to simultaneously obtain precise values for both the position and momentum of the particle for any given point in time. This principle was known as the Heisenberg Uncertainty Principle .
This new approach completely invalidated Bohr’s model , with its clearly defined circular orbits. The modern model of the atom describes the positions of the electrons in an atom in terms of probabilities. An electron can be found potentially at any distance from the nucleus , but depending on its energy level it tends to be more frequently in certain regions around the nucleus than in others; these zones are known as atomic orbitals .
Importance
The importance of this theory cannot be overstated. It has been said (for example, Nobel Prize winner Richard Feynman ) that atomic theory is the most important theory in the history of science . This is due to the implications it has had, both for basic science and for the applications that have derived from it.
All modern chemistry and biochemistry are based on the theory that matter is made up of atoms of different elements, which cannot be transmuted by chemical methods. For its part, chemistry has allowed the development of the pharmaceutical , petrochemical , and fertilizer industries , the development of new materials, including semiconductors, and other advances.
