Atomic Structure Timeline History of Atomic Theory

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<ul><li><p>Atomic Structure TimelineHistory of Atomic Theory</p></li><li><p>Essential QuestionsWhat does it mean when my science teacher says stuff cannot be created or destroyed?</p><p>What is matter made up of? And who figured it out?</p></li><li><p>Evolution of Modern Atomic Theory</p></li><li><p>Democritus (400 B.C.)Proposed that matter was composed of tiny indivisible particles</p><p>Not based on experimental data</p><p>Greek: atomos</p></li><li><p>The Early AtomAristotle succeeded Democritus and did not believe in atoms. Instead, he thought that all matter was continuous. It was his theory that was accepted for the next 2000 years. </p></li><li><p>Alchemy (next 2000 years)Mixture of science and mysticism. Lab procedures were developed, but alchemists did not perform controlled experiments like true scientists.</p></li><li><p>Lavoisier 1777French chemist, who is considered the founder of modern chemistry. Lavoisier clarified the concept of an element as a simple substance that could not be broken down by any known method of chemical analysisHe devised the Law of Conservation of Mass </p></li><li><p>Basic Laws of MatterLaw of Conservation of Mass- mass is neither created nor destroyed during ordinary chemical reactions or physical changes. CH4 + 2O2 2H2O + CO2 16g + 64g 36g + 44g Antoine Lavoisierstated this about 1785</p></li><li><p>Alka Seltzer in WaterZiploc bagAlka seltzer tabletWater</p><p>Using the reaction between the tablet and the water, prove that the Law of Conservation of matter is true.</p></li><li><p>Antoine Lavoisier and his wife, Marie-Anne"It took them only an instant to cut off that head, and a hundred years may not produce another like it." Joseph-Louis Lagrange </p></li><li><p>Proust (1794)Proust stated the Law of Definite Proportions. The law states that the ratio of elements in a compound is always the same. </p></li><li><p>Basic Laws of MatterLaw of Definite Proportions no matter how much salt you have, it is always 39.34% Na and 60.66% Cl by mass.</p><p>Example: Sodium chloride always contains 39.34% Na and 60.66% Cl by mass.</p><p>2NaCl 2Na + Cl2100g 39.34g + 60.66g116.88g ? + ?Joseph Louis Prouststated this in 1794.</p></li><li><p>John Dalton (1808)Dalton add his own - the Law of multiple proportions He proposed a theory to summarize and explain these three lawsI was a school teacher at the age of 12!</p></li><li><p>Basic Laws of MatterLaw of Multiple Proportions- Two or more elements can combine to form different compounds in whole-number ratios.Example John Dalton proposed this in 1803.</p></li><li><p>John DaltonDaltons Four Postulates1.Elements are composed of small indivisible particles called atoms.2.Atoms of the same element are identical. Atoms of different elements are different.3.Atoms of different elements combine together in simple whole number ratios to create compounds.4.In a chemical reaction, atoms are rearranged, but not changed.</p></li><li><p>John Daltons Elements</p></li><li><p>Was Dalton right?</p></li><li><p>Was Dalton right?</p></li><li><p>Essential QuestionsSo, Dalton figured out the atom, how did we figure out what the inside of an atom looks like?</p></li><li><p>How Big (Small) Is the Nucleus of an Atom?If the total atom was the size of a football field, then the nucleus would be the size of an apple in the middle of the field. </p></li><li><p>How Small is an Atom?The width of a human hair = 1,000,000 carbon atoms across</p><p>One bucket full of water contains more atoms than there are bucketfuls of water in the Atlantic ocean</p></li><li><p>Discovery of the ElectronIn the late 1870s many experiments were performed in which electric current was passed through gases at low pressures due to the fact that gases at atmospheric pressure dont conduct electricity well.These experiments were carried out in glass tubes called cathode-ray tubes or Crookes tubes for the man that developed them. </p></li><li><p>Crookes TubeCRT</p></li><li><p>J. J. Thomson (1903)Cathode Ray Tube Experimentsbeam of negative particlesDiscovered particles smaller than the atom!</p></li><li><p>J.J. Thomson (1903)Proved that the atom was divisible and that all atoms contain electrons.This contradicted Daltons Atomic Theory.This allowed a new model of the atom.</p></li><li><p>J. J. Thomson (1903)Plum-pudding Modelpositive sphere (pudding) with negative electrons (plums) dispersed throughout</p><p></p></li><li><p>Robert Millikan (1910s) American physicistDetermined the mass and charge of an electronOil drop experiment</p><p> </p></li><li><p>Oil Drop ExperimentMillikan dropped negatively charged microscopic oil particles into a chamber containing metallic plates and viewed them with a microscope.By applying voltage to the metallic plates, Millikan created an electric field. </p><p>He was able to suspend the oil droplets by adjusting the electric field to the appropriate strength and direction to overcome gravity. </p></li><li><p>Oil Drop ExperimentKnowing the mass of the droplets and the strength of the electric field necessary to suspend them, he was able to calculate the charge of the electron.He noticed that the charge was always a whole-number multiple of 1.602 X10-19 Coulombs.</p></li><li><p>Ernest Rutherford (1911)Gold Foil ExperimentDiscovered the nucleusdense, positive charge in the center of the atomNuclear Model</p></li><li><p>Gold Foil Experiment</p></li><li><p>Gold Foil ExperimentAs expected, most of the alpha particles passed straight through with little or no deflection.However, 1/8000 of the positively charged alpha particles were deflected, some back at the source.</p></li><li><p>Gold Foil Experiment</p></li><li><p>Gold Foil ExperimentFrom this experiment, Rutherford discovered that there must be a very densely packed positively charged bundle of matter within the atom which caused the deflections.He called this positive bundle the nucleus.He tried this experiment with other metals and found the same results.</p></li><li><p>Gold Foil ExperimentThe volume of the nucleus was very small compared to the volume of the atom.Therefore, most of the atom was composed of empty space. </p></li><li><p>It was about as believable as if you had fired a 15-inch shell at a piece of tissue paper, and it came back and hit you.</p><p>-Ernest Rutherford</p></li><li><p>Ernest Rutherford (1911)Nuclear Model </p></li><li><p>Lets take a breakWork with a partner to complete the Rutherfords Gold Foil Experiment</p></li><li><p>Evolution of Modern Atomic Theory</p><p>Almost there!+--------</p></li><li><p>Niels Bohr (1913)Met with J.J. Thomson but didnt impress himWorked with Rutherford and liked his model of the atomIncorporated idea of quantum mechanics into the Rutherford model</p></li><li><p>Niels Bohr (1913)Introduced the idea of electrons traveling around the nucleus in orbits or energy levels.Like the planets, there are multiple orbits like concentric circles around the nucleusPlanetary Model</p></li><li><p>Niels Bohr (1913)He used Bright-Line Spectrumtried to explain presence of specific colors in hydrogens spectrumBuilt upon Max Plancks concepts of quantized energy</p></li><li><p>Erwin Schrdinger (1926)Treats electrons as wavesTells us the probability of finding an electron at any given location at any given momentElectron cloud model Atomic orbital: region around the nucleus where electrons are likely to be found</p></li><li><p>Erwin Schrdinger (1926)Electron Cloud Model (orbital)dots represent probability of finding an e- not actual electrons </p></li><li><p>James Chadwick (1932)Studied under Rutherford and built upon his modelDiscovered neutronsneutral particles in the nucleus of an atom</p></li><li><p>He projected alpha particles (from a decaying polonium) towards beryllium target.The particles released are uncharged and have the same mass as protons. He called them neutrons. </p></li><li><p>James Chadwick (1932)Neutron Modelrevision of Rutherfords Nuclear Model </p></li><li><p>Models of the Atom TimelineLets recap with a video (10:52) </p></li><li><p>Dogs teaching Atoms;list=FLTWKpM0RNaHUX5DRoXcf7qw&amp;index=2</p></li><li><p>Atomic Timeline Poster ProjectDivide into 7 groups and make a poster that includes:Year of discoveryName of modelName of scientist (s)Picture of the model Picture of equipment used in discoveryKey information about model </p></li><li><p>Poster projectGroup 1 Dalton (pg 104-105)Group 2 Thompson (pg 108 110)Group 3 Millikan (pg. 109)Group 4 Rutherford (pg. 111-113)Group 5 Niels Bohr (handout)Group 6 - Schrdinger (pg. 152-155)Group 7 Chadwick (pg. 113-114)</p></li></ul>