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Timeline of Contributions to Atomic Theory

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Megan Kezell

on 17 September 2012

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Transcript of Timeline of Contributions to Atomic Theory

Megan Kezell Timeline of Contributions to
Atomic Theory Early Greeks Erwin Schrödinger Democritus came up with Dalton's Atomic Theory, which stated that all matter is made up of atoms which are indivisible and indestructible
all atoms of a given element are identical in mass and properties
compounds consist of 2 or more different kinds of atoms
a chemical reaction is a rearrangement of atoms
the two updates to Dalton's Theory:
1. atoms are made of smaller parts
2. atoms have isotopes and are not all alike
the two chemistry laws that Dalton based his theory upon
1. Law of Conversation of Mass
2. Law of Definite Proportions John Dalton discovered the negative material within the atom (an electron) using the cathode ray experiments
a beam of charged gas was deflected by the negative magnet leading him to believe the gas contained negative particles
Thomson's model was named the Plum Pudding Model JJ Thomson made models of the atom
called it the planetary model because it proposed that an electron is found only in specific circular paths or orbits around the nucleus
in Bohr's model there are 2 electrons in the first energy level, 8 electrons in the second energy level, 18 electrons in the third level, and so on James Chadwick Robert Milikan carried out his oil drop experiment, in which he measured the electric charges on tiny falling water (and later oil) droplets
his study established that any particular droplet's electrical charge is a multiple of a definite, fundamental value — the electron's charge
he determined the charge mass ratio of the electron by using his oil drop experiment Ernest Rutherford used the alpha particles and gold foil experiment to discover the nucleus of the atom by shooting alpha particles toward a thin sheet of gold foil and determined that the atom is mostly emptied space with a dense positive core he called the nucleus
expected the alpha particles would pass straight through when they encountered the gold atoms, but when the alpha particles hit the gold foil most of the particles passed through but some bounced back
knew that the nucleus was positively charged because it was the particle that deflected Niels Bohr confirmed the existence of the neutron, a particle with no charge but contributing to the mass of the atom
discovered the existence of a neutral subatomic particle 460 B.C. 1803 Eugen Goldstein 1886 discovered anode rays (also called canal rays), the positively-charged particles formed when electrons are removed from the gas particles in a cathode-ray tube
showed that cathode rays can cast shadows, then demonstrated how such rays are emitted, perpendicular to the cathode surface, and can be manipulated with magnetic fields. This suggested the presence of the proton
sometimes credited for discovering the proton Hantaro Nagaoka 1896 the first to present a Saturnian atomic model that looks like Niels Bohr’s atomic model in that the electrons orbit like Saturn’s rings around the nucleus which itself contains a positive electric charge
the model led to speculation that the electrons turning around the atomic nucleus would slowly lose energy and ultimately collide with the nucleus
there was no experimental proof for Nagaoka's model so it was not supported
it can be called an extremely advanced model even though it was not properly evaluated 1897 1898 1908 Albert Einstein 1917 concluded that any increase in energy (E) causes a corresponding increase in mass (m), and that these increases are related by the speed of light in a vacuum (c) squared, E=mc²
proposed that electromagnetic radiation must consist of quantums or photons
dealt with problems of statistical mechanics and quantum theory, which led to his explanations of particle theory and the motion of molecules
investigated the thermal properties of light which laid the foundation of the photon theory of light
applied the general theory of relativity to model the structure of the universe as a whole Kaluza and Klein 1921 the Kaluza- Klein theory is a model which seeks to unify the two fundamental forces of gravitation and electromagnetism
Kaluza discovered that if general relativity is extended to a five-dimensional spacetime, the equations can be separated out into ordinary four-dimensional gravitation plus an extra set, which is equivalent to Maxwell's equations for the electromagnetic field, plus an extra scalar field known as the "dilaton"
Klein proposed that the fourth spatial dimension is curled up in a circle of very small radius, and that a particle moving a short distance along that axis would return to where it began
the distance a particle can travel before reaching its initial position is said to be the size of the dimension 1922 Louis de Broglie 1923 discovered the wave nature of electrons
the wave and particle interpretations of light and matter were seen as being at odds with one another, but Louis de Broglie suggested that these seemingly different characteristics were instead the same behavior observed from different perspectives — that particles can behave like waves, and waves (radiation) can behave like particles
his theory helped explain how atoms, molecules, and protons behave 1926 Werner Heisenberg 1932 his theory of quantum mechanics offered a matrix method to explain stationary discrete energy states
his uncertainty principle, which states that it is impossible to accurately measure both position and momentum (energy and time) concurrently, and that the more precisely we know an object's position the less precisely we can know its momentum, and vice versa
explained the principle of isotopic spin (isospin), a quantum number which arises from regarding different members of a charge multiplet as different states of a single particle 1932 Wolfgang Pauli 1945 explained the theory of relativity with unprecedented clarity
his most famous discovery, the Pauli exclusion principle, which states that no two electrons (or, technically, fermions) can exist in the same quantum state (no two electrons in an atom can have the same four quantum numbers).
introduced his fourth quantum number, or a fourth degree of freedom, to explain characteristics of the hydrogen atom that had puzzled other physicists
proposed the existence of neutral particles of low mass but with spin, the neutrino
proposed a quantum number for the "spin" of electrons, with two possible values, "up" and "down" Murray Gell-Mann 1951 discovered cosmic ray particles that came to be called kaons and hyperons
developed the concept of strangeness for particles, explaining with a quantum number why some hadrons decay rapidly by the strong nuclear force while others decay more slowly by the weak force, contrary to previous theories
proposed the Eightfold way, a new classification system for baryons (heavy subatomic particles) to explain the almost infinitely complex kinds of particles in collisions involving atomic nuclei.
discovered the quark, omega-minus particles believed to be fundamental building blocks of neutrons, protons, and matter itself Friedrich Hund 1966 discovered the principle of quantum tunneling (quantum mechanical barrier penetration)
helped introduce the method of using molecular orbitals to determine the electronic structure of molecules and chemical bond formation
did significant work on the structures of atoms and molecules, molecular orbital theory known as the Hund-Mulliken theory George Zweig 1969 made discoveries concerning the classification of elementary particles and their interactions
proposed the existence of quarks
realized that several important properties of particles such as baryons (protons and neutrons) could be explained by treating them as triplets of other constituent particles (which he called aces and Gell-Mann called quarks), with fractional baryon number and electric charge
Zweig was partly led to his picture of the quark model by the peculiarly attenuated decays of the meson to π, a feature codified by what is now known as the OZI Rule, the "Z" in which stands for "Zweig"
Zweig's quarks were amount to "constituent quarks"
investigated what happens to sound when it enters the ear, and how the brain maps sound onto the spatial dimensions of the cerebral cortex,which lead to the discovery of the continuous wavelet transform
developed the device known as the SigniScope, which simulates the response of the inner ear to speech 1100 B.C. - 146 B.C. started the atomic theory
came up with the explanation/idea of the atom
stated that all matter is made up of units that move around in a void, he called them atoms meaning uncuttable in Greek created Schrödinger equation off of wave mechanics, that describes the form of the probability waves that governs the motion of small particles, and it specifies how these waves are altered by eternal influences
established the correctness of the equation by applying it to the hydrogen atom, predicting many of its properties with remarkable accuracy
the equation is used extensively in atomic, nuclear, and solid-state physics elements were composed of atoms
atoms of different elements have different physical properties
people: Thales of Milectus, Pythagoras, Alhazen, Empedocies, Democritus, Aristotle, and Aristarches Source Citations: http://www.infoplease.com/A0956225.html




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