Students were divided in groups, each one studying in deep different aspects and scientists who all contributed to the discovery of the modern model of the atom.
Aristotle did not believe in the atomic theory and he taught so otherwise. He thought that all materials on Earth were not made of atoms, but of the four elements, Earth, Fire, Water, and Air. He believed all substances were made of small amounts of these four elements of matter. Most people followed Aristotle’s idea, causing Democritus’ idea- which was that all substances on Earth where made of small particles called atoms- to be over looked for about 2,000 years! Aristotle's view was finally proven incorrect and his teachings are not present in the modern view of the atom. During the Middle Age the most diffused atomistic theory was that of Aristotle because it was the nearest of cristian doctrines. During the Reinassence Democritus Theory was discovered again by John Dalton who dispoved Aristotle atomic theory.
1.All matter consists of invisible particles called atoms. 2. Atoms are indestructible. 3. Atoms are solid but invisible. 4. Atoms are homogenous. 5. Atoms differ in size, shape, mass, position, and arrangement.
Thales is the first philosopher in the Greek tradition. Thales made a great progress in his time about the structure of matter. He thought “things” as varying forms of one primary and ultimate element. Of course, today we know that his ideas about water is wrong.
Scholar Dalton came to the conclusion that matter is discontinuous , that is made up of particles . He based on Lavoisier’ s law (the law of conservation of mass) and Proust’ s (the law of definite proportions), to which he added his own ( the law of multiple proportions) , he formulated the first atomic theory of matter . This theory can be summed up as follows : -all matter is made of atoms. Atoms are indivisible and indestructible; -all atoms of a given element are identical in mass and properties; -compounds are formed by a combination of two or more different kinds of atoms; -when elements react, their atoms combine in simple, whole-number ratios -when elements react, their atoms sometimes combine in more than one simple, whole-number ratio.
Eugen Goldstein, (born Sept. 5, 1850, Gleiwitz, Prussia—died Dec. 25, 1930, Berlin) was a German physicist known for his work on electrical phenomena in gases and on cathode rays; he is also credited with discovering canal rays. Goldstein studied at the University of Breslau, where he received his doctorate in 1881.
Joseph John Thomson was born on the18th December in 1856 from scottish parents. Before the beginning of the First World War , he did a big discover : the isotopes . In the 1918 he began Master at Trinity College of Cambrige, where he also died, on the 30th August 1940. His body has been buried in the Abbey of Westminister near Isaac Newton. One of his first assistent, Newall wrote: " J.J. was very awkward with his fingers, and I found it very necessary not to encourage him to handle the instruments! But he was very helpful in talking over the ways in which he thought things ought to go."
In 1869 a Russian chemist called Dmitri Mendeleev (1834-1907) published a periodic table. Mendeleev also arranged the elements known (that were identified 63 of ones) at the time in order of relative atomic mass, but he did some other things that made his table much more successful. He realised that the physical and chemical properties of elements were related to their atomic mass in a 'periodic' way, and arranged them so that groups of elements with similar properties fell into vertical columns in his table. First he put elements into their correct places in the table. In some cases the relative atomic mass had been wrongly calculated by others. By correcting the relative atomic mass he put the element in the correct place. At the time, relative atomic masses (then called atomic weights) were laboriously determined using the formula: atomic weight = equivalent weight x valency The combining weights were generally accurate but sometimes an element was given the wrong valency. But Mendeleev's periodic table was in error because when the elements were arranged by mass it resulted in several elements being placed in groups of elements with differing properties. In addition Mendeleev didn’t predict the discovery of a whole new Group of elements, the noble gases. It’s curios also that if you look at the periodic table with attention, you can see an element called 101 Md. It was Mendelevium. The name derived from Dmitri Mendeleev.
Ernest Rutherford (born Aug. 30, 1871, Brightwater – Oct. 19, 1937 Cambridge). « It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you. On consideration, I realized that this scattering backward must be the result of a single collision, and when I made calculations I saw that it was impossible to get anything of that order of magnitude unless you took a system in which the greater part of the mass of the atom was concentrated in a minute nucleus. It was then that I had the idea of an atom with a minute massive centre, carrying a charge. »
Ernest Rutherford was a Thomson’s pupil who wanted to confirm his master’s atomic model. Considering the recent discovered of the anodic rays by Lord Goldstein, Rutherford tried to do an experiment that had an opposite result compared to what he expected. Because of (/thank to) this experiment he went against Thomson’s model and he revolutionized the concept of atom. In the 1911 Rutherford held the idea that the atom – which represents the microscopic world – could have a structure like the solar system –macroscopic world-. So in his atomic model there is a nucleus that would be the Sun and all the planets that go around are the electrons and they move in the electron cloud.
A rarefied gas was enclosed in a transparent tube , the ends of which were fixed two metal plates , called electrodes . A plaque was attached to the negative terminal of a powerful electric generator and the other to the positive . The negative plate was called cathode ( - ) and the positive plate anode ( + ) . It was assumed that the cathode rays are emitted unknown nature , called cathode rays , which propagate in a straight line , they hit the glass wall making it fluorescent. The actual nature of the cathode rays was unveiled using the Crookes tube , he was able to demonstrate that the radiation of the fluorescent rays consisted of negatively charged particles , to which gave the name of carriers of electricity and , later, of " electrons " . It can thus be stated that: the atoms of all elements contain the same negative particles , called " electrons " .
Niels Bohr (1885-1962) was a Danish physicist who received the Nobel Prize in Physics in 1922 for his contribution to the quantum theory and atomic structure. Bohr was also a philosopher and conceived the principle of complementarity. The young Niels was very tall, strong and a little wrangler (he hit some of his classmates). He was not very able in studying languages, but he showed a predisposition for science since childhood. His professor of chemistry remembered him as a great destroyer of glass containers. During World War II, he also offered a place for Jewish Scientists to live and work. After Denmark was occupied by the Germans, he had a famous meeting with Heisenberg, who had become the head of the German nuclear energy project. Than Bohr, fearing arrest by Germans, escaped to Britain from where he went to the US to work on the Manhattan Project. It led to the development of the first atom bomb. Moreover, to strengthen his theories he kept in touch with others scientists including Albert Einstein. Their first meeting took place in April 1920, when Bohr went to Berlin for a conference, than they became true friends. Einstein, in a letter addressed to Bohr in 1926, made his famous remark on quantum mechanics, often paraphrased as "God does not play dice with the universe", to which Bohr replied "Do not tell God how to play”.
The Raisin Pudding Model of the Atom (Eugen Goldstein) Goldstein used a gas discharge tube which had a perforated cathode. When a high electrical potential of several thousand volts is applied between the cathode and anode, faint luminous "rays" are seen extending from the holes in the back of the cathode. These rays are beams of particles moving in a direction opposite to the "cathode rays," which are streams of electrons which move toward the anode. Goldstein called these positive rays Kanalstrahlen, "channel rays" or "canal rays", because they were produced by the holes or channels in the cathode. In 1907 a study of how this "ray" was deflected in a magnetic field, revealed that the particles making up the ray were not all the same mass. The lightest ones, formed when there was some hydrogen gas in the tube, were calculated to be about 1840 times as massive as an electron. They were protons.
James Chadwick was born in 1891 in England. He worked to make the atomic bomb during the Second World War. He discovered the neutron in 1932 thanks to some experiments made by other scientists( Walther Bothe and Herbert Becker). He tried to strike light elements , like beryllium, lithium or boron, with polonium’s Alpha particles. In this way they got particularly piercing radiations. J. Chadwick realized that those radiations could not be gamma rays, but they were neutrons. These are too much unstable and above all neutrons can easily through elements. All the particles lose energy overstepping the matter, while neutrons have no charge so they lose less of it. A moon’s crater has been called with his own name.
Thomson suggested a first "full" atomic model in 1897. It was called " plum pudding" ( it is an English Christmassy cake) model because the positively charges are concentreted in one central sphere , while the electrons are based on the sphere like candieds fruits are based on the pudding. This model is also knew as " chocolate chip cookie model" or " blueberry muffin model". According to this pattern the atom has got a circle form, in it there are the same number of both positively and negative charges that made the atom neutral.
“All of physics is either impossible or trivial. It is impossible until you understand it, and then it becomes trivial.”
In the early years of the twentieth century a new theory was presented in order to coherently explain . This theory come from the need to conciliate the new discoveries of the period with the previous theory, in particular the paradox of the ultraviolet catastrophe: according with the Classical mechanics, a black body (physical body that absorbs all incident electromagnetic radiation) should emit radiation with infinite power. The main innovation consists of the introduction of the concept of quantization of energy, or else the lower limit of the energy that can be transmitted: the Planck constant, from the name of the German physicist that theorized it and quantized her value, laying the groundwork of the new theory that He theorized in next years wining the Nobel Prize in 1918; the introduction of the study of comportment of matter and energy considering concurrently a wave nature and a corpuscular one, called wave-particle duality, described in the Principle of Complementarity, introduced by Niels Bohr in 1927 for explain how is possible that the description of phenomena that happen in microscopic scale requires characteristics of the particles of the waves, and the demonstration of the impossibility to study concurrently the position and the momentum of a particle, because measuring one of the dimensions the other one is altered, so when the precision of one of the two dimension grow up, the other one decreases, and this is the Heisenberg's uncertainty principle.
Niels Bohr proposed the Bohr Model of the Atom in 1915 thatis based on the Rutherford’s one.The Bohr Model contains some errors, but it is important because it describes most of the accepted features of atomic theory. It explains how electrons can have stable orbits around the nucleus. It establishes that: -Electrons move around the nucleus in definite, closed and circular paths called orbits. Each orbit is associated with a specific amount of energy therefore also called as energy level. -The energy of the orbit is related to its size. The lowest energyis found in the smallest orbit because of the attraction of the nucleus. -Radiation is absorbed or emitted when an electron moves from one orbit to another.
Whilst lacks in Bohr's quantum theory of the atomic structure were coming to light, a young German physicist called Werner Karl Heisenberg published a breaktrough paper in which he stated that the mechanical variables of particles in motion, such as their position, momentum, force etc. could be represented by complex mathematical structures: the matrices. For instance, let p be the momentum of a particle at a given time~t: while in classical mechanics this is given by the (1.1), in Heisenberg matrix mechanics p is a set of components defined by a matrix. Just as an appropriate equation holds in terms of m and v in classical mechanics, so does an appropriate matrix in terms of pn (measurements of the mean values of p over time) in matrix mechanics, so as to satisfy the quantum postulate of discreteness. This new theory elegantly granted a final formalization to the unclear postulates of Bohr's theory of the atomic structure.
Together with Heisenberg's paper, the Austrian physicist Erwin Schrödinger published a study (the result of a work over de Broglie's matter-wave hypotesis) in which he presented a new quantum theory based on a differential equation whose solutions represent the probabilistic mean values of the mechanical variables of a particle in motion. The function which is the result of this equation was called "wave function", and was denoted as ψ(r,t), where r is the position vector in three-dimensional space, and t is time. Although the historical origins of this equation is motivated by de Broglie's idea that this is a real wave accompanying the particle in its motion, it was soon realized that the correct interpretation is the one that only gives the wave function the meaning of a mathematical aid for the calculation of an expectation value of the physical variable that is meant to be measured. Spatially, this results into a probabilistic area wherein the particle exists, rather than a defined path. Applied to the atomic structure this theory gave birth to the modern concept of "atomic orbitals" or "electron clouds", the regions where electrons are more likely to be found within an atom. The probability of finding an electron in a given sector of the orbital is directly linked to the orbital's probabilistic density in that sector and to the wavefunction ψ.
At first, the two newborn theories seemed to be completely divergent, but within a year they were shown to be physically equivalent, mostly by Paul Dirac, an English physicist and partly by Schrödinger himself. Wave mechanics instantly became popular, perhaps more popular than matrix mechanics, due to its mathematical similarity to classical field theory which is why it looked and still looks simpler to many. A consequence to this unification was the discovery, by Heisenberg, of the uncertainity principle (3.1), asserting a fundamental limit to the precision with which certain pairs of physical properties of a particle (known as complementary variables), such as position x and momentum p, can be known simultaneously. This is due to the fact that a measurement of one of these variable would affect the variable itself and its companion property, thus resulting in an uncertainity over the whole measurement. It has since become clear, however, that the uncertainty principle is inherent in the properties of all wave-like systems, and that it arises in quantum mechanics simply due to the matter-wave nature of all quantum objects. Thus, the uncertainty principle actually states a fundamental property of quantum systems, and is not a statement about the observational success of current technology. It must be emphasized that measurement does not mean only a process in which a physicist-observer takes part, but rather any interaction between classical and quantum objects regardless of any observer. The uncertainty principle puts an end to determinism as Isaac Newton had originally theorized and Laplace had revised. According to Newton, it would have been sufficient to know the position and velocity of a body at any given time in order to calculate all its previous and future states through the laws of classical physics. Along with the concept of orbital, the uncertainity principle represented an important step towards the definitive conceptualization of the quantum theory and the behaviour of fundamental particles.
Later in the years, the discovery of new and smaller particles led to the makeup of the \textit{Standard Model of Fundamental Particles and Interactions}, dividing particles in two classes: \textit{fermions} and \textit{bosons}. Fermions make up matter, bosons carry forces. This particles have been classified in therms of \textit{spin}, their intrinsic angular momentum, given in units of $\hbar$ (Reduced Planck Constant), which is the unit of quantum angular momentum. Fermions have half-integer spin, while bosons have integer spin (e.g.: a neutron has spin $\sfrac{1}{2}$, a photon has spin 1). This gave a final formalization to Pauli's exclusion principle, which had been formulated in 1925 in terms of \textit{quantum numbers}, thus conciliating the Model with the earlier (but still not obsolete) work made by the first quantum physicist at the beginning of the XX Century. \\The great work of Paul Dirac in unifying matrix and wave mechanics and his attempts to conciliate them with Maxwell's theory of electromagnetism culminated in an equation (4.1) that describes all spin-$\sfrac{1}{2}$ massive particles such as electrons and quarks, and is consistent with both the principles of quantum mechanics and the theory of special relativity giving birth to the \textit{Quantum Field Theory} (or QFT) which is the modern version of quantum mechanics. The equation also implied the existence of a new form of matter, antimatter, previously unsuspected and unobserved and which was experimentally confirmed several years later. The idea that antiparticles and antiatoms could exist brought a whole new kind of questions in every single branch of physics, especially cosmology and astronomy, resulting from the fact that almost all matter observable from the Earth seems to be made of matter rather than antimatter. These misteries still remain unsolved, as well as greater and deeper problems regarding the structure of our Universe, it components and their origins. \\To quote Shakespeare: {The best is yet to come}".
The quark theory was put forward in 1964 by the American physicists Murray Gell-Mann and George Zweig, they hypothesized that can explain the properties of hadrons composed of quarks considering elementary. The name "quark", chosen by Murray Gell-Mann, is a meaningless term in a passage from the novel Finnegans Wake by James Joyce, he was reading at the time of the studies: "Three quarks for Muster Mark! Sure he has not got much of a bark And sure any he has it's all beside the mark".
In particle physics quark is an elementary fermion participating in the strong interaction. In nature there are never isolated, but united in composite particles called hadrons, such as the proton and the neutron. Quarks are fermions, which are grouped into three generations, each consisting of two leptons and two quarks (plus their antiparticles called antiquarks). In total originate in this way six types or flavors of quarks: the first generation is composed of up and down quarks; the second includes the charm quark and the strange quark; the third is composed of the top quark and the bottom quark.
The concept is erroneous credited to Italian scientist Carlo Rubbia, a Nobel Prize nuclear physics and former director of Europe's CERN international nuclear physics lab. He published a proposal for a power reactor based on a proton cyclotron accelerator with a beam energy of 800 MeV to 1 GeV, and a target with thorium as fuel and lead as a coolant. However, years before, Dr. C.D. Bowman working at Los Alamos national laboratory proposed the fundamental of the concept in published papers.
In nuclear physics, an energy amplifier is a novel type of nuclear power reactor, a subcriticl reactor, in which an energetic particle beam is used to stimulate a reaction, which in turn releases enough energy to power the particle accelleretor and leave an energy profit for power generation. The concept has more recently been referred to as an accelerator-driven system (ADS) or Accelerator-driven-sub-critical reactor.
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