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Slide 1 of 19 Chemsitry Chemsitry)) – Section 2.1 Science 9 – Unit B ((Chemsitry Early View of the Elements Ancient Greeks believed all matter was made of 4 elements called Earth, Air, Water and Fire They thought properties like heat, dryness, cold, and moisture could be explained by this Evolving Theories of Matter Democritus Slide 3 of 19 Slide 2 of 19 Science 9 – Unit B (Chemistry) – Section 2.1 Metallurgy A Greek named Democritus believed otherwise, and many agreed with him “Chemistry” came from khemeia: Greek for “juice of a plant” Democritus believed: Between 6000 and 1000 B.C.E., valuable metals such as gold and copper were made by metallurgy 1) matter could be broken down into indivisible bits called atomos: modern-day “atoms” 2) different atoms made different materials 3) combining different atoms made new materials Science 9 – Unit B (Chemistry) – Section 2.1 Early Metallurgy involved smelting, in which pure metals are extracted from ores (containing metal compounds) using high heat Gold was one of the first metals to be extracted, followed by copper, silver, lead and tin Science 9 – Unit B (Chemistry) – Section 2.1 1 Slide 5 of 19 Slide 4 of 19 Metallurgy Alchemy Gold is valuable, because it is flexible (easy to work with) and does not oxidize easily (stays shiny) Alchemists tried to make gold out of other materials, but were unsuccessful (sadly) Raw copper is brittle but can be annealed (heated) to make it strong and malleable; this made excellent tools, pots and weapons! They were not scientists, but they: developed common glassware like beakers, flasks and filters The Iron Age started by extracting iron from rocks and smelting it into pots and swords invented plaster of Paris When first discovered, mercury was called “quicksilver” after its lustre and liquid state invented distillation and a technique of making common mineral acids wrote Alchemia, the first chemistry textbook From Bacon to Boyle Science 9 – Unit B (Chemistry) – Section 2.1 Slide 7 of 19 Slide 6 of 19 Science 9 – Unit B (Chemistry) – Section 2.1 Lavoisier In the 16th century, Sir Francis Bacon wrote a book arguing that the foundation of science should be experimental evidence Lavoisier continued their work by defining an element as a pure substance that cannot be broken down (decomposed) further Boyle (17th century) suggested two things: He identified 23 of the modern elements this way 1) The purpose of chemistry is to determine what all materials are made of Lavoisier also performed many chemical reactions 2) Individual elements could be combined to form compounds He measured masses of reactants (going in) and products (coming out) very carefully Bacon and Boyle rocked the scientific community Science 9 – Unit B (Chemistry) – Section 2.1 He developed the Law of Conservation of Mass Science 9 – Unit B (Chemistry) – Section 2.1 2 Law of Conservation of Mass: In a chemical change, the total mass of the new substances is always the same as the total mass of the original substances So, all the atoms that went into the reaction come out, but get rearranged into new substances Matter is neither created nor destroyed, but only changes form! Slide 9 of 19 Slide 8 of 19 Lavoisier Law of Definite Composition: Compounds are pure substances that contain two or more elements combined together in fixed (or definite) proportions This relationship allows compounds to form ex. every molecule of H2O is made of 2 atoms of hydrogen (H) and 1 atom of oxygen (O) Dalton revived Democritus’ ideas and came up with his “billiard ball” model: Science 9 – Unit B (Chemistry) – Section 2.1 Slide 11 of 19 Slide 10 of 19 Science 9 – Unit B (Chemistry) – Section 2.1 Dalton and Atomic Theory Law of Definite Composition Dalton and Atomic Theory Dalton revived Democritus’ ideas and came up with his “billiard ball” model: 1) All matter is made up of small particles called atoms (atoms are solid spheres, nothing inside) 4) Atoms of one element are different in mass and size from the atoms of other elements 2) Atoms cannot be created, destroyed, or divided into smaller particles 5) Compounds are created when atoms of different elements link together in definite proportions 3) All atoms of the same element are identical in mass or size Science 9 – Unit B (Chemistry) – Section 2.1 Science 9 – Unit B (Chemistry) – Section 2.1 3 Slide 13 of 19 Slide 12 of 19 Development of Atomic Theory Development of Atomic Theory Dalton was incorrect about one thing: atoms can now be divided into smaller particles! J.J. Thomson used special gas discharge tubes to determine that a smaller particle (electron) existed But…at the time, he was correct The electron is a “smaller particle” of an atom His work was a pivotal stage in the development of the model of the atom So many scientists contributed at least one idea to the framework of modern atomic theory This is the spirit of science at its best! Development of Atomic Theory Thomson posited that the atom was a giant sphere of positive (+) charge with negatively-charge (-) electrons embedded throughout He called this the “plum pudding” model, where the atom has areas of positive and negative charge Science 9 – Unit B (Chemistry) – Section 2.1 Science 9 – Unit B (Chemistry) – Section 2.1 Slide 15 of 19 Slide 14 of 19 Science 9 – Unit B (Chemistry) – Section 2.1 Development of Atomic Theory Ernest Rutherford believed that if you fired radiation at an atom, it would bounce right back to the source What he discovered is that radiation will scatter in many different directions by the electrons, and backscatter off the center! Science 9 – Unit B (Chemistry) – Section 2.1 4 Rutherford added the following to atomic theory: 1) Nearly all the atom’s mass is in a central nucleus 2) Most of an atom’s volume is empty space 3) Electrons surround the nucleus 4) The positive charge comes from protons in the nucleus Slide 17 of 19 Slide 16 of 19 Development of Atomic Theory Development of Atomic Theory This “solar system” model of the atom changed to look like the diagram on the right Chadwick discovered the neutron as the second particle in the nucleus 5) There must be a second particle in the nucleus Development of Atomic Theory Niels Bohr refined the atomic model to explain more of the properties of the atom Science 9 – Unit B (Chemistry) – Section 2.1 Slide 19 of 19 Slide 18 of 19 Science 9 – Unit B (Chemistry) – Section 2.1 Development of Atomic Theory The exact location of an electron may not be determined, but the energy of each shell may be predicted or measured The work of scientists like de Broglie and Schrodinger has led to the quantum cloud view of the atom (the quantum mechanical model) He arranged the electrons into different orbits called “electron shells” In it, we know the chances of finding an electron in one area of the atom (a cloud of probability) Science 9 – Unit B (Chemistry) – Section 2.1 Science 9 – Unit B (Chemistry) – Section 2.1 5