Gregg.Duffy.Ramos.Spring2010.AtomicTimeline.

Atomic History Timeline

Democritus Democritus was born in Abdera, the leading Greek city on the northern coast of the Aegean Sea, in the year 460 BC. Although the ancient accounts of Democritus's career differ widely, they all agree that he lived to a ripe old age, 90 being the lowest figure. Therefore this would put his death around 370 BC. Democritus agreed that everything which is must be eternal, but denied that "the void" can be equated with nothing. This makes him the first thinker on record to argue the existence of an entirely empty "void". In order to explain the change around us from basic, unchangeable substance he created a theory that argued that there are various basic elements which always existed but can be rearranged into many different forms. Democritus' theory argued that atoms only had several properties, particularly size, shape, and (perhaps) weight; all other properties that we attribute to matter, such as color and taste, are but t he result of complex interactions between the atoms in our bodies and the atoms of the matter that we are examining. Furthermore, he believed that the real properties of atoms determine the perceived properties of matter--for example, something that is solid is made of small, pointy atoms, while something that has water like properties is made of large, round atoms. Some types of matter are particularly solid because their atoms have hooks to attach to each other; some are oily because they are made of very fine, small atoms which can easily slip past each other. In Democritus' own words: //By convention there is sweet, by convention there is bitterness, by convention hot and cold, by convention color; but in reality there are only atoms and the void.//

[] []

John Dalton John Dalton (1766–1844) was born into a modest Quaker family in Cumberland, England, and earned his living for most of his life as a teacher and public lecturer, beginning in his village school at the age of 12. After teaching 10 years at a Quaker boarding school in Kendal, he moved on to a teaching position in the burgeoning city of Manchester. There he joined the Manchester Literary and Philosophical Society, which provided him with a stimulating intellectual environment and laboratory facilities. The first paper he delivered before the society was on color blindness, which afflicted him and is sometimes still called "Daltonism."He proceeded to calculate atomic weights from percentage compositions of compounds, using an arbitrary system to determine the likely atomic structure of each compound. If there are two elements that can combine, their combinations will occur in a set sequence. The first compound will have one atom of A and one of B; the next, one atom of A and two atoms of B; the next, two atoms of A and one of B; and so on. Hence, water is HO. Dalton also came to believe that the particles in different gases had different volumes and surrounds of caloric, thus explaining why a mixture of gases—as in the atmosphere—would not simply layer out but was kept in constant motion. Dalton consolidated his theories in his //New System of Chemical Philosophy// (1808–1827). []

Marie Curie Marie Sklodowska Curie (1867–1934) was the first person ever to receive two Nobel prizes: the first in 1903 in physics, shared with her husband Pierre and Henri Becquerel for the discovery of the phenomenon of radioactivity; and the second in 1911 in chemistry for the discovery of the radioactive elements polonium and radium. The daughter of impoverished Polish schoolteachers, Marie worked as a governess in Poland to support her older sister in Paris, whom she eventually joined. Already entranced with chemistry, Marie took advanced scientific degrees at the Sorbonne, where she met and married Pierre Curie, a physicist who had achieved fame for his work on the piezoelectric effect. For her thesis she chose to work in a field just opened up by Wilhelm Roentgen's discovery of X-rays and Becquerel's observation of the mysterious power of samples of uranium salts to expose photographic film. She soon convinced her husband to join in the endeavor of isolating the "radioactive" substance—a word she coined. In 1898, after laboriously isolating various substances by successive chemical reactions and crystallizations of the products, which they then tested for their ability to ionize air, the Curies announced the discovery of polonium, and then of radium salts weighing about 0.1 gram that had been derived from tons of uranium ore. []



W.K. Roentgen was born in 1845 from a wealthy family of dealers in the small city of Lennep, in north-western Germany; after having spent the most greater part of the infancy in the Low Countries, to the twenty year-old age he transferred later to Zurich and three years he/she graduated him in engineering near the Technische Hochschule. Although you/he/she had not followed some course of experimental physics during the studies, definite to develop searches in this sector after the diploma. After having received the doctorate in 1869, Roentgen got a series of charges as teacher in various German universities and in collaboration with Kundt it performed careful studies on the behavior of the subject; for example it was the first one to show, with a thermometer done in house, that is easier to heat the damp air that the dry air. Roentgen had quarantatré years when it became teacher of physics and manager of the institute of Physics of the university of Wurzburg, a prosperous Bavarian town; he/she lived with his/her wife Bertha in an ample apartment to the second floor of the institute that understood a communicating study with a private laboratory. In June 1894 it started to study the cathode rays, to that time matter of very popular search and the night of November 8 th 1895 during one of his/her experiments it reached the discovery of a type of rays of unknown nature that called "X rays." Three weeks later spread Roentgen the news of his/her discovery: the fact to be able to see through the objects without breaking them and inside the human body aroused great sensation. In consequence of this he acquired a great fame and in 1901 you/he/she was assigned him the first Nobel prize for the physics Roentgen died in 1923. http://www.akisrx.com/inglese/htm/roentgen.htm

JJ Thomson



In 1897 the physicist Joseph John (J. J.) Thomson (1856–1940) discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube—an area being investigated by numerous scientists at the time. Thomson interpreted the deflection of the rays by electrically charged plates and magnets as evidence of "bodies much smaller than atoms" that he calculated as having a very large value for the charge to mass ratio. Later he estimated the value of the charge itself. In 1904 he suggested a model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces. His efforts to estimate the number of electrons in an atom from measurements of the scattering of light, X, beta, and gamma rays initiated the research trajectory along which his student Ernest Rutherford moved. Thomson's last important experimental program focused on determining the nature of positively charged particles. Here his techniques led to the development of the mass spectroscope, an instrument perfected by his assistant, Francis Aston, for which Aston received the Nobel Prize in 1922. The plum pudding model of the atom by J.J. Thomson, who discovered the electron in 1897, was proposed in 1904 before the discovery of the atomic nucleus. In this model, the atom is composed of electrons, surrounded by a soup of positive charge to balance the electron's negative charge, like negatively-charged "plums" surrounded by positively-charged "pudding". The electrons were thought to be positioned throughout the atom, but with many structures possible for positioning multiple electrons, particularly rotating rings of electrons. Instead of a soup, the atom was also sometimes said to have had a cloud of positivecharge. [] []

Ernest Rutherford

Ernest Rutherford was born in Brightwater, New Zealand, into a family of pioneer stock who had emigrated from Britain less than 30 years earlier. Although he was a very good all-round scholar while at school, Rutherford showed no real bias to science. In 1890 he entered Canterbury College at Christchurch in New Zealand, where his scientific ability became apparent, and graduated with first-class degrees in both science and mathematics. Rutherford proposed that the atom contained a massive //nucleus// containing all of its positive charge, and that the much lighter electrons were outside this nucleus. The nucleus had a radius about ten thousand times smaller than the radius of the atom, only ten femtometers, or one hundred thousand billionth of a meter. Scattering at large angles occurred when the alpha particles came near to a nucleus. The reason that most alpha particles were not scattered at all was that they were passing through the relatively large 'gaps' between nuclei. Rutherford revised Thomson's 'plum pudding' model, showing how electrons could orbit a positively charged nucleus, like planets orbiting a sun. In 1915 Neils Bohr adapted Rutherford's model by saying that the orbits of the electrons were quantized, meaning that they could exist only at certain distances from the nucleus. The Rutherford model of the atom was soon superseded by the Bohr model, which used some of the early quantum mechanical results to give locational structure to the behavior of the orbiting electrons, confining them to certain circular (and later elliptical) planar orbits. In the Bohr model, expanding on the work of Henry Moseley, the central charge was identified as being directly connected with the atomic number (that is, the element's place on the periodic table). Since the Bohr model is an improvement on the Rutherford model in this and other ways, some sources combine the two, referring to the Bohr model as the Rutherford-Bohr model. However, even an atom with a core containing an atomic number of charges was the work of a number of men, including those mentioned, and also lesser known workers such as Antonius Van den Broek.

The Rutherford model was important because it essentially proposed the concept of the nucleus, although this word is not used in the paper. What Rutherford notes as the (probable) concomitant of this results, is a "concentrated central charge" in the atom: "Considering the evidence as a whole, it seems simplest to suppose that the atom contains a central charge distributed through a very small volume, and that the large single defluxions are due to the central charge as a whole, and not to its constituents." The central charge containing most of the atom's positive charge, invariably later become associated with a concrete structure, the atomic nucleus. After the Rutherford model and its confirmation in the experiments of Henry Moseley and its theoretical description in the Bohr model of the atom, the study of the atom branched into two separate fields, nuclear physics, which studies the nucleus of the atom, and atomic physics which studies atom's electronic structure. [] []

Robert Millikan



Robert Andrews Millikan (March 22, 1868 – December 19, 1953) was an American experimental physicist, and Nobel laureate in physics for his measurement of the charge on the electron and for his work on the photoelectric effect. He served as president of Caltech from 1921 to 1945. The purpose of Robert Millikan and Harvey Fletcher's oil-drop experiment (1909) was to measure the electric charge of the electron. They did this by carefully balancing the gravitational and electric forces on tiny charged droplets of oil suspended between two metal electrodes. Knowing the electric field, the charge on the oil droplet could be determined. Repeating the experiment for many droplets, they found that the values measured were always multiples of the same number. They interpreted this as the charge on a single electron: 1.602 × 10−19 coulomb (SI unit for electric charge). []

Henri Becquerel

Antoine Henri Becquerel (15 December 1852 – 25 August 1908) was a French physicist, Nobel laureate, and one of the discoverers of radioactivity. He won the 1903 Nobel Prize in Physics for discovering radioactivity. French physics Professor Antoine Henri Becquerel discovered that uranium compounds produced rays that blacked photographic plates. Radioactivity or radioactive is the name of the property possessed by some elements of spontaneously emitting energetic particles and rays from their atomic nuclei. These emitted particles or rays are called radiation. An elemental material (such as uranium) that emits radiation is called radioactive material. Most, but not all, atomic nuclei are stable i.e. not radioactive. Radioactivity is a naturally occurring process that occurs when an unstable nucleus goes through a transformation, moving to a lower energy state accessible to the nucleus. The nuclei apart releasing energy in order to become stable. Nature always universally prefers to seek its lowest energy state. []

Erwin Schrodinger

Erwin Rudolf Josef Alexander Schrödinger (12 August 1887 – 4 January 1961) was an Austrian theoretical physicist who achieved fame for his contributions to quantum mechanics, especially the Schrödinger equation, for which he received the Nobel Prize in 1933. In 1935, after extensive correspondence with personal friend Albert Einstein, he proposed the Schrödinger's cat thought experiment. []

Werner Heisenberg Werner Heisenberg (5 December 1901 in Würzburg–1 February 1976 in Munich) was a German theoretical physicist, best known for enunciating the Kramers-Heisenberg dispersion formula. He made important contributions to quantum mechanics, nuclear physics, quantum field theory, and particle physics. The Kramers-Heisenberg dispersion formula is an expression for the cross section for scattering of a photon by an atomic electron. It was derived before the advent of quantum mechanics by Hendrik Kramers and Werner Heisenberg in 1925, based on the correspondence principle applied to the classical dispersion formula for light. The quantum mechanical derivation was given by Paul Dirac in 1927. The Kramers-Heisenberg formula was an important achievement when it was published, explaining the notion of "negative absorption" (stimulated emission), the Thomas-Reiche-Kuhn sum rule, and inelastic scattering - where the energy of the scattered photon may be larger or smaller than that of the incident photon – thereby anticipating the Raman effect. []

//**Niels Henrik David Bohr** was born in Copenhagen on October 7, 1885, as the son of Christian Bohr, Professor of Physiology at Copenhagen University, and his wife Ellen, née Adler. Niels, together with his younger brother Harald (the future Professor in Mathematics), grew up in an atmosphere most favourable to the development of his genius - his father was an eminent physiologist and was largely responsible for awakening his interest in physics while still at school, his mother came from a family distinguished in the field of education.

After matriculation at the Gammelholm Grammar School in 1903, he entered Copenhagen University where he came under the guidance of Professor C. Christiansen, a profoundly original and highly endowed physicist, and took his Master's degree in Physics in 1909 and his Doctor's degree in 1911.

http://nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-bio.html

James Chadwick



James Chadwick discovered the neutron in 1932, resulting in the solution of the jig-saw puzzle for the weight of atoms. His discovery formed the base for the investigation of the tougher questions of nuclear physics: the nature of the nucleus and its forces. In 1935, he received the Nobel Prize for Physics. Chadwick was knighted in 1945, and died in 1974 at Cambridge.

Chadwick was born in 1891 in Manchester, England. He was graduated from Manchester University in 1911 and remained to work with Ernest Rutherford. In 1913, he received a scholarship to study in German, placing him in Germany at the beginning of World War I. After Chadwick was detained as a civilian prisoner of war, he returned to England in 1919 to carry out research at Cambridge University. In 1923, he became the assistant director of research at the Cavendish Laboratory.

Rutherford discovered that atoms have minute and dense nuclei, with the nucleus holding a positive charge in the charge of a hydrogen nucleus. Physicists wanted to determine where the extra mass was living. Chadwick helped answer this question when identifying the neutron (particle without an electric charge in the nucleus) in 1932. Chadwick had created an experiment to answer the question of this unknown nucleus mass source.

Chadwick smashed alpha particles into beryllium, a rare metallic element, and allowed the radiation that was released to hit another target: paraffin wax. When the beryllium radiation hit hydrogen atoms in the wax, the atoms were sent into a detecting chamber. In physics it is known that only a particle having almost the same mass as a hydrogen atom could effect hydrogen in that manner. The experiment results showed a collision with beryllium atoms would release massive neutral particles, which Chadwick named neutrons //.// This provided the answer for hidden mass in atoms.

Chadwick's discovery advanced experimental work for all scientists. Since neutrons have no electrical charge, any neutrons fired from a source has the ability to go through deep layers of materials and to go into the nuclei of the target atoms. After Chadwick's work, scientists world-wide began bombardment of all types of materials with neutrons. It was discovered that when uranium is a target, nuclear fission becomes possible, resulting in nuclear weapons and nuclear power plants.

In 1935, Chadwick received the Nobel Prize for Physics for this discovery. During World War II, he worked with the British atomic bomb project, and was a science advisor to Oppenheimer on the Manhattan Project. The Manhattan Project was the first time an atomic bomb had been produced. Chadwick was knighted in 1945, and died in 1974 at Cambridge.

After having received the doctorate in 1869, Roentgen got a series of charges as teacher in various German universities and in collaboration with Kundt it performed careful studies on the behavior of the subject; for example it was the first one to show, with a thermometer done in house, that is easier to heat the damp air that the dry air. Roentgen had quarantatré years when it became teacher of physics and manager of the institute of Physics of the university of Wurzburg, a prosperous Bavarian town; he/she lived with his/her wife Bertha in an ample apartment to the second floor of the institute that understood a communicating study with a private laboratory. In June 1894 it started to study the cathode rays, to that time matter of very popular search and the night of November 8 th 1895 during one of his/her experiments it reached the discovery of a type of rays of unknown nature that called "X rays." Three weeks later spread Roentgen the news of his/her discovery: the fact to be able to see through the objects without breaking them and inside the human body aroused great sensation. In consequence of this he acquired a great fame and in 1901 you/he/she was assigned him the first Nobel prize for the physics Roentgen died in 1923.
 * W.K. Roentgen was born in 1845 from a wealthy family of dealers in the small city of Lennep, in north-western Germany; after having spent the most greater part of the infancy in the Low Countries, to the twenty year-old age he transferred later to Zurich and three years he/she graduated him in engineering near the Technische Hochschule. Although you/he/she had not followed some course of experimental physics during the studies, definite to develop searches in this sector after the diploma.

Electron cloud model ||

Electron Cloud Model There are three important people that all contributed greatly to the discovery of the electron cloud model. They are Ernest Rutherford, Neils Bohr, and Werner Heisenberg. Rutherford brought to the table that the center of an atom had the positive charge and mass were concentrated in the middle. Neils Bohr taking what Rutherford had said came up with the theory that electrons are constricted to predetermined orbits and can transition between orbits on absorbing or emitting energy. Werner Heisenberg suggested that the only way to describe the location of an electron is through the probability of distribution. Heisenburg’s suggestion formed the basis of the electron cloud model. The electron cloud model shows the most probable locations of electrons in an atom. Where the cloud is denser is where you will most likely find an electron. The purpose of the electron cloud model is to describe the location of electrons around the nucleus.

Rutherford-Bohr Model The Rutherford-Bohr Model is the quantum model for the hydrogen atom. Electrons in an H2 atom moves around the nucleus only in certain allowed circular orbits. The model fits the quantized energy levels of the H2 atom and postulates only certain circular orbits for the electron. When the electron becomes more tightly bound, its energy becomes more positive. Although this model was a great discovery, there were two limitations. The first limitation was that the model is not applicable for any other atom except hydrogen. The second limitation was that the model is fundamentally incorrect.

Atomic Planetary Model

Rutherford tested J.J. Thomson’s plum pudding model with the “gold foil” experiment. He suggested that if Thomson was right the mass would spread throughout the atom. So hypothetically if you shoot high velocity alpha particles at an atom there should be very little to deflect the alpha particles. Some of the alpha particles deflected directly back. This meant that Thomson’s plum pudding model was incorrect. The only way the alpha particles would deflect directly backwards is if the mass of the atom was concentrated in the nucleus. This is how Rutherford came up with the atomic planetary model.

Plum Pudding Model Atoms are made up of electrons which are negatively charged particles. Atoms are electrically neutral, which means they have some positively charged particles as well. Scientists in the early 20th century became curious about how many charged particles were in the atom and how they were arranged. Thomson was the first scientist to respond to these curiosities. In 1904 he proposed an atomic model. In Thomson’s model each atom was a sphere filled with positively charged fluid. Thomson mad the suggestion that the positive fluid held the negative charges. This model was called the plum pudding model because the electrons are like raisins dispensed in pudding