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chemistry_chapter2notes - Chapter 2 Atoms and Elements 2.1...

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Chapter 2: Atoms and Elements 2.1 Imaging and Moving Individual Atoms Scanning Tunneling Microscope (STM): a technique that can image, and even move, individual atoms and molecules works by moving an extremely sharp electrode over a surface and measuring the resulting tunneling current o electrode – an electrical conductor o tunneling current – the electrical current that flows between the tip of the electrode and the surface even though the two are not in physical contact Elements: There are about 91 different naturally occurring elements Scientists have succeeded in making over 20 synthetic elements (not found in nature) 2.2 Early Ideas about the Building Blocks of Matter Leucippus and Democritus (Greek philosophers of the 5 th century): theorized that matter was ultimately composed of small, indivisible particles called atomos proposed that many different kinds of atoms existed, each different in shape and size, and that they moved randomly through empty space Plato and Aristotle (5 th century): theorized that matter had no smallest parts and that different substances were composed of various proportions of fire, air, earth, and water o this idea prevailed Copernicus (1473-1542): proposed that the sun, not Earth, was at the center of the universe o marks the beginning of what we now call the scientific revolution The next 200 years—with the works of scientists such as Francis Bacon (1561–1626), Johannes Kepler (1571–1630), Galileo Galilei (1564–1642), Robert Boyle (1627– 1691), and Isaac Newton (1642–1727)—brought rapid advancement as the scientific method became the established way to learn about the physical world John Dalton (English chemist: 1766-1844): offered convincing evidence that supported the early atomic ideas of Leucippus and Democritus Page | 1
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2.3 Modern Atomic Theory and the Laws That Led to It 3 Laws Leading to the Atomic Theory: 1. Law of Conservation of Mass – In a chemical reaction, matter is neither created nor destroyed Consistent with the idea that matter is composed of small, indestructible particles. o The particles rearrange during a chemical reaction, but the amount of matter is conserved because the particles are indestructible(at least by chemical means) 2. Law of Definite Proportions – All samples of any given compound, regardless of their source or how they were prepared, have the same proportions of their constituent elements hints at the idea that matter might be composed of atoms o Compounds have definite proportions of their constituent elements because they are composed of a definite ratio of atoms of each element, each with its own specific mass. Since the ratio of atoms is the same for all samples of a particular compound, the ratio of masses is also the same 3. Law of Multiple Proportions – When two elements (call them A and B) form two different compounds, the masses of element B that combine with 1 g of element A can be expressed as
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chemistry_chapter2notes - Chapter 2 Atoms and Elements 2.1...

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