Part One - The Science and Building Blocks of Life 1

2. The Chemistry of Life 20

2.1 What Are the Chemical Elements That Make Up Living Organisms? 21 An element consists of only one kind of atom 21 Protons: Their number identifies an element 22 Neutrons: Their number differs among isotopes 23 Electrons: Their behavior determines chemical bonding 23 2.2 How Do Atoms Bond to Form Molecules? 25 Covalent bonds consist of shared pairs of electrons 25 Multiple covalent bonds 27 Ionic bonds form by electrical attraction 27 Hydrogen bonds may form within or between molecules with polar covalent bonds 29 Polar and nonpolar substances: Each interacts best with its own kind 29 2.3 How Do Atoms Change Partners in Chemical Reactions? 30 2.4 What Properties of Water Make It So Important in Biology? 31 Observation is an important skill 13 The scientific method combines observation and logic 13 Good experiments have the potential of falsifying hypotheses 14 Statistical methods are essential scientific tools 15 Not all forms of inquiry are scientific 16 An Overview and a Preview 36