{"id":140,"date":"2018-03-19T15:47:55","date_gmt":"2018-03-19T15:47:55","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-orgbiochemistry\/chapter\/atomic-theory\/"},"modified":"2018-07-31T18:59:02","modified_gmt":"2018-07-31T18:59:02","slug":"atomic-theory","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-monroecc-orgbiochemistry\/chapter\/atomic-theory\/","title":{"raw":"2.2 Atomic Theory","rendered":"2.2 Atomic Theory"},"content":{"raw":"
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Learning Objectives<\/h3>\r\n
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  1. Describe the modern atomic theory.<\/li>\r\n \t
  2. Use atomic theory to explain various observations about matter.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n

    Take some aluminum foil. Cut it in half. Now you have two smaller pieces of aluminum foil. Cut one of the pieces in half again. Cut one of those smaller pieces in half again. Continue cutting, making smaller and smaller pieces of aluminum foil.<\/p>\r\n

    It should be obvious that the pieces are still aluminum foil; they are just becoming smaller and smaller. But how far can you take this exercise, at least in theory? Can you continue cutting the aluminum foil into halves forever, making smaller and smaller pieces? Or is there some limit, some absolute smallest piece of aluminum foil?\u00a0 Thought experiments like this\u2014and the conclusions based on them\u2014were debated by philosophers like Democritus as far back as the fifth century BCE.<\/p>\r\n

    The modern atomic theory<\/span><\/strong><\/span>, proposed about 1803 by the English chemist John Dalton (Figure 2.2 \"John Dalton\"<\/a>), is a fundamental concept that states that all elements are composed of very tiny indivisible atoms, that each element is composed of a different type of atom, and that all chemical reactions involve whole atoms changing their bonds.<\/p>\r\n

    In Chapter 1 \"Chemistry, Matter, and Measurement\"<\/a>, we defined an atom as the smallest part of an element that maintains the identity of that element. Individual atoms are extremely small; even the largest atom has an approximate diameter of only 5.4 \u00d7 10\u221210<\/sup> m. It takes over 18 million of these atoms, lined up side by side, to equal the width of your little finger (about 1 cm).\u00a0 A carbon atom has a mass of only about 2 x 10-23 <\/sup>g, or to put it another way,\u00a0 6.02 x 1023<\/sup> carbon atoms together have a mass of about 12 grams.<\/p>\r\n\r\n

    \r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"298\"]\"image\" Figure 2.2 John Dalton.<\/em> John Dalton was an English scientist who enunciated the modern atomic theory.[\/caption]\r\n

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    Some elements in their pure form exist as individual atoms. For example, a macroscopic chunk of iron metal is composed, microscopically, of individual atoms. Other elements, however, exist as bonded groups of atoms called molecules. Several important elements exist as two-atom combinations and are called diatomic molecules<\/span><\/strong><\/span>. In representing a diatomic molecule, we use the symbol of the element and include the subscript 2 to indicate that two atoms of that element are bonded together. The elements that exist as diatomic molecules are hydrogen (H2<\/sub>), oxygen (O2<\/sub>), nitrogen (N2<\/sub>), fluorine (F2<\/sub>), chlorine (Cl2<\/sub>), bromine (Br2<\/sub>), and iodine (I2<\/sub>).<\/p>\r\n\r\n

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    Looking Closer: Atomic Theory<\/h3>\r\n

    Dalton\u2019s ideas are called the modern<\/em> atomic theory because the concept of atoms is very old. The Greek philosophers Leucippus and Democritus originally introduced atomic concepts in the fifth century BC. (The word atom<\/em> comes from the Greek word atomos<\/em>, which means \u201cindivisible\u201d or \u201cuncuttable.\u201d) Dalton had something that the ancient Greek philosophers didn\u2019t have, however; he had experimental evidence, such as the formulas of simple chemicals and the behavior of gases. In the 150 years or so before Dalton, natural philosophy had been maturing into modern science, and the scientific method was being used to study nature. So when Dalton announced a modern atomic theory, he was proposing a fundamental theory to describe many previous observations of the natural world; he was not just participating in a philosophical discussion.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n

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    Concept Review Exercises<\/h3>\r\n
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      What is the modern atomic theory?<\/p>\r\n\r\n<\/div><\/li>\r\n \t

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      What are atoms?<\/p>\r\n\r\n<\/div><\/li>\r\n<\/ol>\r\n<\/div>\r\n

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      Answers<\/h3>\r\n[reveal-answer q=\"550884\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"550884\"]\r\n\r\n1. The modern atomic theory states that all matter is composed of atoms.\r\n\r\n2. Atoms are the smallest parts of an element that maintain the identity of that element.[\/hidden-answer]\r\n
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      Key Takeaways<\/h3>\r\n