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Chem 101 Chapter 2- Atoms and Elements

Chem 101 Chapter 2- Atoms and Elements - The Basic Tools of...

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Stardust A wide array of elements make up planet Earth and every living thing on it. What is science’s view of the cosmic origin of these elements that we take for granted in our environment and in our lives? The “big bang” theory is the generally accepted theory for the origin of the universe. This theory holds that an unimaginably dense, grapefruit-sized sphere of matter exploded about 15 billion years ago, spewing the products of that explosion as a rapidly ex- panding cloud with a temperature in the range of 10 30 K. Within 1 second, the universe was populated with the particles we explore in this chapter: protons, electrons, and neutrons. Within a few more seconds, the universe had cooled by millions and millions of de- grees, and protons and neutrons began to combine to form helium nuclei. After only about 8 minutes, scientists believe, the universe was about one-quarter helium and about three-quarters hydrogen. In fact, this is very close to the composition of the universe today, 15 billion years later. But humans, animals, and plants are built mainly from carbon, oxygen, nitrogen, sulfur, phosphorus, iron, and zinc—heavier elements that have only a trace abundance in the universe as a whole. Where do these heavier elements come from? The cloud of hydrogen and helium cooled over a period of thou- sands of years and condensed into stars like our sun. There hydrogen atoms fuse into more helium atoms and energy streams outward. Every second on the sun, 700 million tons of hydrogen is converted to 695 million tons of helium, and 3.9 10 26 joules of energy is evolved. Gradually, over millions of years, a hydrogen-burning star be- comes more and more dense and hotter and hotter. The helium atoms initially formed in the star begin to fuse into heavier atoms—first carbon, then oxygen, and then neon, magnesium, silicon, phospho- 2 Atoms and Elements Dr. Christopher Burrows, ESA/STSc1 and NASA. The Basic Tools of Chemistry The supernova of 1987. When a star becomes more and more dense, and hotter and hotter, it can become a “red giant.” The star is unstable and explodes as a “supernova.” One such spectacular event occurred in a distant star in 1987. These explosions are the origin of the heavier elements, such as iron, nickel, and cobalt. 58
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59 Chapter Outline 2.1 Protons, Electrons, and Neutrons: Development of Atomic Structure 2.2 Atomic Number and Atomic Mass 2.3 Isotopes 2.4 Atomic Weight 2.5 Atoms and the Mole 2.6 The Periodic Table 2.7 An Overview of the Elements, Their Chemistry, and the Periodic Table 2.8 Essential Elements Chapter Goals See Chapter Goals Revisited (page 89). Test your knowl- edge of these goals by taking the exam-prep quiz on the General ChemistryNow CD-ROM or website. Describe atomic structure and define atomic number and mass number.
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Chem 101 Chapter 2- Atoms and Elements - The Basic Tools of...

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