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Atomic Structure Timeline Project
Transcript of Atomic Structure Timeline Project
400 B.C Contribution Democritus developed the idea of an atom . He believed that atoms are present in all forms of existence for instance , solid or liquid . He also believed that all atoms are individually created and cannot be separated , no matter what scientific methods are applied . Solid Sphere Model Democritus Of Adbera Continued Nuclear Model Aristotle
Mid 300's Contribution Aristotle disagreed with Democritus's atomic theory. He was not able to see how atoms could stay in perpetual motion in void . Aristotle’s theory made a great generalization off all matter being made of the four elements: fire, water, earth, and air. He also believed that there were four qualities to these elements: dryness, hotness, coldness, and moistness. Based on these beliefs fire would hold the characteristics of being dry and hot, water is wet and cold, air is hot and wet, while the earth is dry and cold. Aristotle John Dalton Solid Sphere Dalton proposed the Law Of Multiple Proportions . This led to the atomic theory proposal of 1803 . Dalton recognized the existence of atoms of elements and that compounds formed the union of these atoms . He therefore assumed that simplest ratios would be used in nature and came up with a formula for water of HO. He then assigned a relative atomic weight of one to hydrogen and developed a relative atomic weight scale from percent composition data and assumed ratios . Nuclear Model Sir William Crookes Discovered cathode rays had the following properties: travel in straight lines from the cathode; cause glass to fluoresce; impart a negative charge to objects they strike; are deflected by electric fields and magnets to suggest a negative charge; cause pinwheels in their path to spin indicating they have mass. Sir William Crookes 1879 Eugene Goldstein Contribution In 1886 Eugen Goldstein noted that cathode-ray tubes with a perforated cathode emit a glow from the end of the tube near the cathode. Goldstein concluded that in addition to the electrons, or cathode rays, that travel from the negatively charged cathode toward the positively charged anode, there is another ray that travels in the opposite direction, from the anode toward the cathode. Because these rays pass through the holes, or channels, in the cathode, Goldstein called them canal rays.Plum Pudding PlumModel Henri Becquerel While studying the effect of x-rays on photographic film , he discovered some chemicals spontaneously decompose and give off very penetrating rays . With this experiment Henri Becquerel discovered and identified radioactivity. Atomic Model J.J Thomson 1897 1896 Used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 10 8 coulombs/gram. Studied "canal rays" and found they were associated with the proton H + .Thomson proposed the "plum pudding" model of the atom. In this model, the volume of the atom is composed primarily of the more massive (thus larger) positive portion (the plum pudding). The smaller electrons (actually, raisins in the plum pudding ) are dispersed throughout the positive mass to maintain charge neutrality Plum Pudding Model Robert Millikan 1897 Robert Millikan conducted an experiment known as the oil drop experiment . This experiment allowed Millikan to find out the mass of an electron . The charge on a drop was always a multiple of 1.59 x 10-19 Coulombs. He proved Thomson's hypothesis that the mass of an electron is at least 1000 times smaller than the smallest atom. Oil Drop Experiment Max Planck 1900 Max Planck suggests that radiation is quantized (it comes in discrete amounts.)Planck explained that energy is not a continuous, flowing entity, but is carried in tiny, discontinuous units, which he named quanta and described as "the pennies of the atomic world". Each quantum's energy is equal to the frequency of radiation multiplied by the universal constant which Planck defined. Quantum Model Ernest Rutherford 1911,1915,1918 He proposed the nuclear atom as the result of the gold-foil experiment in 1911. Rutherford proposed that all of the positive charge and all of the mass of the atom occupied a small volume at the center of the atom and that most of the volume of the atom was empty space occupied by the electrons. This was a very radical proposal that flew in the face of Newtonian Physics. Although positive particles had been discussed for some time, it was Rutherford in 1920 that first referred to the hydrogen nucleus as a proton. Also in 1920, Rutherford proposed the existence of the third atomic particle, the neutron.
Atomic Planetary Model nucleus-red
electrons-green Niels Bohr 1912 Niels Bohr applies quantum theory to Rutherford's atomic structure by assuming that electrons travel in stationary orbits defined by their angular momentum. This led to the calculation of possible energy levels for these orbits and the postulation that the emission of light occurs when an electron moves into a lower energy orbit. Bohr Model Francis Aston 1920 Francis Aston invented the mass spectrograph in 1920. He was the first person to observe isotopes. For example he observed that there were three different kinds of hydrogen atoms. While most of the atoms had a mass number of 1 he also observed hydrogen atoms with mass numbers of 2 and 3. Modern atomic masses are based on mass spectral analysis. His work led Rutherford to predict the existence of the neutron. Francis Aston's experiment Louis de Broglie 1924 Discovered that electrons had a dual nature-similar to both particles and waves. French quantum physicist Louis de Broglie introduced his theory of particle-wave duality in 1924. In his time, the wave and particle interpretations of light and matter were seen as being at odds with one another, but 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. Louis De Broglie Model Erwin Schrodiner 1926 Erwin Schrodiner developed wave mechanics, which describes the behavior of quantum systems for bosons.Edwin Schrodinger stated that rather than electrons being distributed within an electron configuration of shells and energy levels, they were arranged in orbitals which were systematically distributed within Electron Clouds. He defined an orbital as: The region of space that surrounds a nucleus in which two electrons may randomly move. Electric Cloud Model Werner Heisenburg 1927 Proposed Principle of Indeterminancy - you can not know both the position and velocity of a particle.Werner's contribution to the atomic theory was that he calculated the behavior of electrons, and subatomic particles that also make up an atom. Instead of focusing mainly on scientific terms, this idea brought mathematics more into understanding the patterns of an atom's electrons. Werner's discovery helped clarify the modern view of the atom because scientists can compare the actually few numbers of atoms there are, by their movements of electrons, and how many electrons an atom contains. Surrounding the outside of an atomic nucleus is an electron cloud, which is a name given to the electrons that are widely spreading and moving around. In conclusion, Werner Heisenberg contributed to the atomic theory by including quantum mechanics, the branch of mechanics, based on quantum theory, used for interpretating the behavior of elementary particles and atoms. Wolfgang Pauli 1930 He stated that electrons orbit the nucleus of the atom. The rule, now called the Pauli exclusion principle, holds that no two electrons in an atom can have the same quantum numbers. An electron in an atom has four such numbers. They define the energy of the electron in terms of the distance of its orbit from the nucleus, the orbit's shape, the orientation of the axis of the orbit, and the electron's spin on its own axis.Pauli also became the first to propose the existence of the subatomic particle the neutrino. He was also one of the first to fully understand the theory of general relativity. James Chadwick 1932 In 1932, while working under Ernest Rutherford at Cambridge, James Chadwick proved the existence of neutrons, the elementary particle without any electrical charge and a fundamental building block of the atom's nucleus. James Chadwick received a Noble Peace Prize for his scientific work . by