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History of the Atomic Theory Ancient Greeks (B.C.) • Aristotle • Four Elements: • • • • Earth Water Air Fire Greek Atomists (460B.C.) • Democritus : Matter was made up of particles in perpetual motion and had the following characteristics: • • • • • • Invisible Solid Indivisible Eternal Surrounded by an empty space Infinite number of Shapes Greek Atomists • Archimedes disagreed with Democritus • Archimedes was very highly respected and so everyone believed what he said • Democritus’ ideas were tossed Alchemy • During the dark ages, earlier information was lost. • During the middle ages, people began to reinvestigate nature and the structure of matter • The plan : TRANSMUTATION Change plain metals into noble metals - Lead Gold - Alchemists developed the Observation Experimentation Measurement Classification Method. Boyle (1661) • Matter was made up of simple substances called ELEMENTS • Elements were substances that could not be further decomposed • He had no PROOF : qualitative experiments (what’s in it) no quantitative experiments (how much) Lavoisier (1780) • Developed quantitative experiments needed to prove Boyle’s theory • He heated mercury in air. • The silver mercury turned to a red product, which was HEAVIER 200g of Mercury (grey) plus 16g Oxygen yields 216 g of red product 200g Hg + 16g O2 216 g HgO Lavoisier • To explain the increase, he reversed the experiment and heated the red product and collected the gas released • Found that the amount of oxygen produced was equal to the increase in mass of his first reaction 216 g of red product (heated) yields 200g of Mercury plus 16g of Oxygen 216 g HgO 200g Hg + 16g O2 Lavosier • Demonstrated the Law of Conservation of Mass; • Matter is neither created nor destroyed during a chemical reaction • Lavoisier classified substances as elements; • A substance that cannot be broken down into simpler substance(s) by chemical means. Lavoisier's table of simple substances Metals Gases New names (French) Old names (English translation) Lumière Light Heat Calorique Oxygène Azote Hydrogène Principle of heat Igneous fluid Fire Matter of fire and of heat Dephlogisticated air Empyreal air Vital air Base of vital air Phlogisticated gas Mephitis Base of mephitis Inflammable air or gas Base of inflammable air New names (French) Old names (English translation) Antimoine Antimony Argent Silver Arsenic Arsenic Bismuth Bismuth Cobolt Cobalt Cuivre Copper Étain Tin Fer Iron Manganèse Manganese Mercure Mercury Molybdène Molybdena Nickel Nickel Or Gold Platine Platina Plomb Lead Tungstène Tungsten Zinc Zinc Lavoisier's table of simple substances Earths Nonmetals New names (French) Old names (English translation) Soufre Sulphur Phosphore Phosphorus Carbone Pure charcoal Radical muriatique Unknown Radical fluorique Radical boracique New names (French) Old names (English translation) Chaux Chalk, calcareous earth Magnésie Magnesia, base of Epsom salt Baryte Barote, or heavy earth Alumine Clay, earth of alum, base of alum Silice Siliceous earth, vitrifiable earth Unknown Unknown Dalton (1808) • Major Contribution: First Atomic theory based on experimental evidence. • Reintroduced the idea of the atom based on scientific experiments. • Small particles called atoms • • • • Can’t be subdivided Can’t be created or destroyed Properties of 1 atom are identical Properties of atoms of different elements differ • Atoms combine in simple ways to form compounds (in definite whole number ratios) Thomson (1897) • Discovered the electron • Proposed an initial model (Thomson’s Pudding) • Sphere of positive substances mixed with negative electrons • AKA Raisin Pudding Model Millikan (1911) • Determined the charge of an electron • Used an oil drop experiment Rutherford (1912) • His students were doing experiments with radiation • Shot alpha particles through a thin sheet of gold foil • Thought that the spaces in the atoms were mainly empty, BUT • Some particles were reflected • Lead to the discovery of the Nucleus • The positive charge (or majority of the atom’s mass) was concentrated in a small point. • Introduced Atomic Planetary Model The Rutherford Experiment Bohr (1914) • Orbits can’t be anywhere – they’re quantified • Quantified – specific numbers (like quarters) • Greater the distance from the nucleus, the greater the energy of an electron • Orbits became known as energy levels • Every atom in its normal (non excited) state, the electrons occupy the lowest energy levels available. • Last in what we know as classical physics Updating Atomic Theory • Scientists have learned a great deal about the structure of matter • Atoms have many parts and a complex organization • The essential ideas of Dalton’s theory are still useful: • Elements are made of atoms • Compounds do form by the joining of atoms in fixed whole number ratios • Properties of atoms of 1 element are identical • Properties of atoms of different elements differ. Updating Atomic Theory • 3 Major Differences: 1. Atoms can be subdivided - Made up of protons, neutrons & electrons 2. Atoms can be changed from one element to another, but only by nuclear reactions 3. Atoms of the same element are not all exactly alike – they are alike in characteristics that determine chemical properties of that element but atoms of the same element can and DO have different masses (Isotopes) Time Line • BC – Ancient Greeks had the idea of an atom • 1808 - Dalton’s atomic theory • 1886 – Protons discovered • 1897 – Electrons discovered • 1911 – Rutherford’s Experiment • 1913 – Bohr Model of an atom • 1932 – Neutron discovered Quantum Physics • Subatomic Particles • Electron probability • Different Shapes • Charge-Cloud Model • Doesn’t show paths of the electrons, instead it shows the most probable location of an electron - Schrödinger A Review • Over the last 200 years, (especially in the 1900s) that many modifications were made to our conception of the structure of matter. • Through the creativity and new technologies utilized by scientists, modifications and improvements were made. • Science, technology and the affect of society’s thinking changed how we think of nature. • Atoms are not solid spheres, but a combination of even smaller parts, each having a unique structure and function.