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Atomic Theory Chemistry with Mr. Torre Atomic Theory *The year zero really does not exist in history. Chemistry Through the Ages Chapter 3 From the beginning of civilization people made use of the elements found in the Earth. Ores were refined to produce metals, and this fact is used to identify periods in history, such as the Bronze Age (3500BC-2000BC) and the Iron Age (1200BC-700AD ). Around 400 BC the Greeks tried to explain chemical changes in what they called the Four Elements : Earth, Wind, Fire, and Water. Democritus (460 –371 BC) hypothesized that all matter is composed of “Atoms,” (From the Greek word “ atmos ” – meaning uncuttable) too small to see. Democritus believed that these atoms could not be split into smaller portions. During the middle ages Alchemists experimented with different chemical materials trying to make gold and silver or immortality. Some alchemists were sincere scientists who discovered some of the elements (such as mercury, sulfur, and antimony). The word “Chemist” comes from “Alchemist” Robert Boyle (1627- 1691) who was the first scientist to recognize the importance of careful measurements, defined element as a sample of matter that cannot be broken down into simpler substances. 1800 John Dalton Dalton’s Atomic Theory 1. Elements are made of atoms 2. All atoms of an element are identical 3. Atoms of an element are different than atoms of any other element. 4. Atoms of different elements combine to form compounds. 5. Atoms cannot be created or destroyed. 1817 Pierre Joseph Pelletier discovered chlorophyll, caffeine, strychnine, colchicine, and quinine. 1856 William Perkin produced first synthetic dye, mauve . 1897 J.J. Thomson ’s experiment (page 55) -Electric current can cause particles to travel through a vacuum from the electrically negative cathode to the positive anode. -The particles are deflected by the negative in an electric field indicating that the particle is also negative. -Since atoms are not negative or positive they must contain negative and positive particles which balance each other. 1900 William Thomson (Lord Kelvin) Negative particles are balanced by positive material - Thomson’s Atomic Model (The Plum surrounding it like raisins in pudding. Pudding Model): 1904 Hantaro Nagaoka developed “Saturnian” system, with electrons orbiting a nucleus in rings. 1911 Earnest Rutherford (page 56) designed the gold foil experiment, in which positive α-particles (alpha particles) passed through gold foil. Some particles were deflected, leading Rutherford to conclude that atoms contain a positive center and mostly open space. 1913 Niels Bohr (1885 – 1962) used the previous discoveries to describe the atom as having a positive nucleus with negative electrons orbiting in rings around the outside. The Bohr Model 1925 Wave Mechanical Model (current model) - An electron can be thought of as a particle, but also as a wave in a discrete (quantized) energy level. - We cannot identify the exact location of an electron, but we can predict a three-dimensional “cloud” where the electron would most probably be. 1945 Nuclear Fission - Atom split - Atomic bomb - Nuclear power 1961 Silicon Chip - Computer chip manufacture on large scale 2001 Human Genome sequenced in draft form Twenty-first Century Nanotechnology - Working with matter as small as a nanometer or 0.000000001m ( 10 -9 meters) - Synthetic molecules designed to function as molecule-sized machines .
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