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CHEM 102: LECTURE 3 The Chemical Revolution of Lavoisier https://upload.wikimedia.org/wikipedia/commons/1/17/Laboratoire-de-Lavoisier.jpg Lavoisier's Laboratory, Musée des Arts et Métiers, Paris Antoine-Laurent Lavoisier (1734 – 1794) forever changed the practice and concepts of chemistry by forging a new series of laboratory analyses that would bring order to the chaotic centuries of Greek philosophy and medieval alchemy. Lavoisier’s experimental work which led to his discovering the Law of Conservation of Mass and framing the principles of modern chemistry in his Traité élémentaire de chimie (the first Chemistry book) prompted future generations to regard him as a founder of the science. It is generally accepted that Lavoisier's great accomplishments in chemistry stem largely from his changing the science from a qualitative to a quantitative one. Lavoisier is most noted for his discovery of the role oxygen plays in combustion. He recognized and named oxygen (1778) and hydrogen (1783), and opposed an earlier (phlogiston) theory of spontaneous chemical reactions. Lavoisier helped construct the metric system, wrote the first extensive list of elements and helped to reform chemical nomenclature. He predicted the existence of silicon (1787) and was also the first to establish that sulfur was an element (1777) rather than a compound. He discovered that, although matter may change its form or shape, its mass always remains the same. The fossil fuel, natural gas (CH4), “burns” in the presence of oxygen. This is called a combustion reaction or simply oxidation. The Law of Conservation of Mass states that Matter can neither be created or destroyed…. but it can be transformed. If you count the number of carbon atoms (black), the number of hydrogen atoms (white) and the number of oxygen atoms (red) on both sides of the chemical reaction below, they are (respectively) the same. This is made definite in the equation which follows by the integers [1 before methane (CH4), 2 before oxygen (O2), 1 before carbon dioxide (CO2) and 2 before water (H2O)]. upload.wikimedia.org/wikipedia/commons/7/7c/Com... Lavoisier’s experiments were carried out using samples of materials that could be weighed; one describes the samples as “macroscopic.” When the discussion center on atoms, the descriptor is “microscopic.” A macroscopic quantity of matter, say a glass of water, has ~ 6 x 10^23 molecules of water. Think of how big a number this is. The bill passed by Congress to ease the economic concerns caused by coronavirus pandemic is 2 trillion dollars, which is 2 x 10^9 , 14 powers of 10 smaller! If you had Chemistry in High School, the specification of the integers [1,2,1,2] was called “balancing the chemical equation.” What you were really being asked to do was to assume that a law deduced from experiments done on a macroscopic scale can be applied to a problem on the microscopic scale of atoms and molecules. That you were able to do so is a profound statement of the universality of a physical law of Nature. This lecture has two objectives. The first is to review the background of ideas that led to Lavoisier’s discovery of the Law of Conservation of Mass. This journey will reveal other Conservation Laws of Nature, statements that are valid not only at the scale of atoms and molecules, but at the scale of everyday macroscopic experiments, and to events/processes on the scale of the Universe. That is why you need to be familiar with these Laws. They apply at every length scale of the Universe, which is why they are called “universal.” The second objective is to bring you “face to face” with Lavoisier by having you read the description “in his own words” of his discovery of the Law of Conservation of Mass, as described his seminal text, Traité élémentaire de chimie, published in 1789. The Classical Theory of Chemistry. 1. Ideas from the Ancient World a) Thales of Miletus (we know he lived around May 28, 585 BC) Thales proposed that there exists ONE (“chemical”) element in Nature. Further, he proposed that that one element, the primary stuff of all things, is water.

F.Copleston, “A History of Philosophy” vol.1, part 1. “… the phenomena of evaporation suggests that water may become mist or air, while the phenomena of freezing might suggest that, if the process were carried further, water could become earth. In any case, the importance of this early thinker lies in the fact that he raised the question, what is the ultimate nature of the world; and not in the answer that he actually gave to the question or in his reasons, be they what they may, for giving the answer.”

b) charge [ 'ηλεκτρον (the substance amber) = electron; ~ 600 BC ] The ancient Greeks recognized that rubbing certain materials (friction) produced changes in that material, particularly with respect to its effect on other materials.

Today we know that charge is a characteristic of an atom or molecule which expresses either the loss or gain of electrons. c) Democritus (468-370 BC) ; Epicurus (342-270 BC) Democritus postulated that matter was not infinitely devisable, but that there was a limit to which it could be divided. The limiting case of minute, indivisible particles he called an atom ( άτομο ).

d) Aristotle (384-212 BC) Apart from his foundational contributions to Philosophy, Aristotle was the first to formulate a theory of Chemistry, and to link this to an explanation of motion. In ancient Greek, his 'kinesis' ( κίνησις ) literally means movement or to move. i) “Chemistry”: four elements on Earth: Earth, Air, Fire, Water ; in the Heavens: a fifth element αἰθήρ = aether; quintessence. ii) “Physics”: All bodies move toward their Natural Place on Earth. For the elements Earth and Water, that place is the center of the (geocentric) universe; the natural place of water is a concentric shell around the earth because earth is heavier; it sinks in water. The natural place of Air is likewise a concentric shell surrounding that of water; bubbles rise in water. The natural place of Fire is higher than that of air but below the innermost celestial sphere (carrying the Moon). 2. Ideas from the Intellectual Revolution in the 17th Century a) mass For nearly 2000 years, people held to Aristotle’s “common sense” theory of “natural place” and motion, that a falling object had a definite “natural falling speed” proportional to its weight. Hence, in dropping two objects of different weight, the heavier object should hit the ground first. In his inclined-plane experiment, the 26 year old Galileo found that the speed just kept increasing, and weight was irrelevant as long as friction was negligible. Both objects hit the ground at the same time. He recognized that the speed (velocity) of an object changes on falling (the concept of acceleration). This groundbreaking experiment was captured in the legend that Galileo dropped two cannonballs from the top of the Leaning Tower in his hometown of Pisa in Italy.