rav65819_ch02_017-032

rav65819_ch02_017-032 - *16 Chapter 2 2 The Nature of...

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***16 Chapter 2 2 The Nature of Molecules introduction ABOUT 12.5 BILLION YEARS AGO, an enormous explosion likely marked the beginning of the universe. With this explosion began a process of star building and planetary formation that eventually led to the formation of Earth, about 4.5 billion years ago. Around 3.5 billion years ago, life began on Earth and started to diversify. To understand the nature of life on Earth, we first need to understand the nature of matter that forms the building blocks of all life. Starting with the earliest speculations about the world around us, the most basic question has always been, “What is it made of?” The ancient Greeks recognized that larger things may be built of smaller parts. This concept was not put on solid experimental ground until the early 20th century, when physicists began trying to break atoms apart. From those humble beginnings to the huge particle accelerators used today, the picture that emerges of the atomic world is fundamentally different from that of the macroscopic world around us. To understand how living systems are assembled, we must first understand a little about atomic structure, about how atoms can be linked together by chemical bonds to make molecules, and about the ways in which these small molecules are joined together to make larger molecules, until finally we arrive at the structure of a cell. Our study of life on Earth therefore begins with physics and chemistry. For many of you, this chapter will be a review of material encountered in other courses. concept outline 2.1 The Nature of Atoms Atomic structure includes a central nucleus and orbiting electrons Electrons determine the chemical behavior of atoms Atoms contain discrete energy levels 2.2 Elements Found in Living Systems The periodic table displays elements according to atomic number and properties 2.3 The Nature of Chemical Bonds Ionic bonds form crystals Covalent bonds build stable molecules Chemical reactions alter bonds
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2.4 Water: A Vital Compound Water’s structure facilitates hydrogen bonding Water molecules are cohesive Water molecules are adhesive 2.5 Properties of Water Water’s high speciFc heat helps maintain temperature Water’s high heat of vaporization facilitates cooling Solid water is less dense than liquid water The solvent properties of water help move ions and polar molecules Water organizes nonpolar molecules Water can form ions 2.6 Acids and Bases The pH scale measures hydrogen ion concentration Buffers help stabilize pH ***17 2.1 The Nature of Atoms Any substance in the universe that has mass and occupies space is defined as matter. All matter is composed of extremely small particles called atoms. Because of their size, atoms are difficult to study. Not until early in the last century did scientists carry out the first experiments revealing the physical nature of atoms. Atomic structure includes a central nucleus and orbiting electrons
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This note was uploaded on 10/15/2010 for the course BIO BIO1 taught by Professor Lipke during the Fall '09 term at CUNY Brooklyn.

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rav65819_ch02_017-032 - *16 Chapter 2 2 The Nature of...

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