tailieunhanh - Chemistry part 2, Julia Burdge,2e (2009)

Chemistry, Julia Burdge, Second Edition. McGraw Hill. | What Do Molecules Look Like Molecules are far too small for us to observe them directly. An effective means of visualizing them is by the use of molecular models. Throughout this book we will represent matter at the molecular level using molecular art the two-dimensional equivalent of molecular models. In these pictures atoms are represented as spheres and atoms of particular elements are represented using specific colors fable lists some of the elements that you will encounter most often and the colors used to represent them in this book. Molecular art can be of ball-and-stick models in which the bonds connecting atoms appear as sticks Figure b or of space-filling models in which the atoms appear to overlap one another Figure c . Ball-and-stick and space-filling models illustrate the specific three-dimensional arrangement of the Sodium Carbon Sulfur Nitrogen Chlorine Bromine Fluorine Iodine Hydrogen atoms. The bad-and-stick model does a good job of illustrating the arrangement of atoms but exaggerates the distances between atoms relative to their sizes. The space-filling model gives a more accurate picture of these interatomic distances but can obscure the details of the three-dimensional arrangement. Figure 1 2 Water represented with a a molecular formula b ball-and-stick model and c space-filling model. b The reactions in Figure are all things that you can observe at the macroscopic level. In other words these processes and their results are visible to the human eye. In studying chemistry you will learn to visualize and understand these same processes at the molecular level. Although it can take many different forms all matter consists of various combinations of atoms of only a relatively small number of simple substances called elements. The properties of matter depend on which of these elements it contains and on how the atoms of those elements are arranged. The Scientific Method Experiments are the key to advancing our understanding of .