BEYOND SIMPLE CHEMISTRY: thresholds of discovery

Over the past two centuries, chemists have refined the atomic and molecular theories of matter and provided convincing explanations for the major features of the world around us. Indeed, it may seem as if there is a chemical explanation for everything that involves matter.

Certainly, chemical knowledge has provided satisfying answers for the examples given in this book. Chemistry today is a rich and diverse science that explains many of the properties of animate and inanimate objects in terms of their chemical composition. But chemistry has many problems left to solve and much more to understand. Indeed, one might say that much of the most difficult work lies ahead.

Today, we know that the properties of all substances depend on the properties of their constituent atoms and molecules. Atomic and molecular properties, in turn, are a consequence of electronic and stereochemical features. The behavior of atoms and molecules is affected by their architecture, including the bonding patterns that give rise to functional groups and the three-dimensional arrangements that constitute stereochemistry. In addition, the electric field associated with atoms and molecules influences their physical and chemical properties. Most of our knowledge of chemical behavior has come from the study of pure— and fairly simple—substances whose molecules are relatively small. In this respect, one can say that the basic work in chemistry is almost completed. Our study of simple chemistry has led to a good understanding of inanimate nature—the elements of the periodic table, the inorganic minerals and compounds, and the common organic substances. We know why materials take a certain form, what gives them stability, and what conditions cause chemical reactions. Now chemistry is moving on toward the difficult work—an improved understanding of the very small, the very large, and the very complicated.

The revolutionary advances in microelectronics that made computers possible have also given chemists access to phenomena at the molecular level. Instruments such as scanning tunneling microscopes or atomic force microscopes can generate images of single atoms on solid surfaces, and key features of reactions occurring on catalyst surfaces can be discovered. Whenever solids react with gases or liquids, the reactions occur on the solid surface. Chemists are now beginning to investigate the ways in which the surface of a solid contributes to the overall reactivity of the material. Many processes involved in environmental chemistry are surface reactions that have only recently been studied, such as the interaction of chemicals with soil, or ozone depletion reactions. The chemistry of the very small also includes pheromone research. Interaction of single pheromone molecules with insect olfactory cells can be detected, and the chemical basis of animal communication is now an important area of research.

The bonding pattern of chlorophyll the green pigment that powers photosynthesis in plants and certain other organisms, is a web of carbon, hydrogen, and oxygen atoms along with carbon groups, all bound to a complex of magnesium and nitrogen.

The chemistry of very large molecules, such as artificial and natural polymers, is another fruitful area of research. Large molecules can now be assembled with good control over bonding arrangements, ensuring that the product molecules will have the desired properties. Chemists talk hopefully of producing molecular wires and molecular machines. In these carefully constructed molecules, chemical events would take the place of electronic or mechanical components. Researchers in genetic engineering and molecular biology seek to understand biological processes in terms of the chemical behavior of large natural polymers such as proteins and deoxyribonucleic acid (DNA). For example, genetic defects are increasingly being understood in terms of DNA chemistry. The fields of chemistry, biochemistry, and molecular biology now share a focus on molecular processes.

The chemistry of the very small and the very large is often hard to understand, but the chemistry of complex systems is always difficult. In biological processes, for example, the knowledge of simple chemistry is only a starting point. Life processes depend on the close interaction of diverse molecular substances in a well-maintained reaction environment—the biological cell. Cellular reactions may be difficult to understand completely, but today’s chemists have most of the necessary tools. Going into the 21st century, discovering more about the molecular basis of life, the science of chemistry is on its most fascinating journey.

A scientist uses a pipette to mark a trail of fire ant pheromone to a food source. This trail will be followed by other fire ants. This type of animal communication is an important area of chemical research.

An image of a silver film produced by a scanning tunneling microscope (STM) reveals its lack of crystalline structure. STM images are capable of showing structures as tiny as molecules and atoms, the basis of the properties of all substances.