Walk onto Caltech's campus from the corner of Wilson and San Pasqual. As you head toward the center, the building you're most likely to miss will be the second on your left. Almost completely obscured by trees except from the rear, where it presents an unlabeled blank wall to a driveway, stands the Arthur Amos Noyes Laboratory of Chemical Physics or Noyes, as it's known to its inhabitants.
I have found that the average layperson, asked to name a famous physical chemist or define physical chemistry, is unable to do either. At most, he or she confuses physical for physiological and assumes an implicit collection to medical science. And who can blame them? There are too many subdivisions of chemistry for a person without a bachelor's degree in the sciences to keep them straight. Analytical, bio, organic, inorganic and physical chemistry or, to add to the confusion, chemical physics. To put it as simply as possible, physical chemists employ the fundamental principles and methods of physics to study aspects of chemical reactions. The more bombastic descriptions claim that physical chemistry research provides the foundation for all of the other subdivisions. Some might add that it does this by fitting everything in the universe to y = mx + b. Strangely, not many people seem to find this as hilarious as physical chemists do.
Scientific research that has technological relevance, that fires the imagination and that is successfully championed by a memorable personality will be viewed as valuable to society. The study of chemistry has much of the first, but little of the latter two. It acquires those qualities through its association with the other sciences, particularly biology. It could be argued that the push for interdisciplinary research has affected biology, physics and astronomy, but I don't think it has become as pervasive as it is in chemistry. Read a handful of grant proposals, and it's easy to see that chemists are unable to justify their research without looking to the other sciences for validation. An awareness of the unknown, of how much there is yet to learn in the field and why it is both necessary and appealing, has been diluted at least in part by the proliferation of prefixes. Rather than improving the accuracy of the definition of areas of study within chemistry, they obfuscate and bewilder. Witness, for instance, the recent development of the field known as "biophysical organic chemistry." I think that "biophysical in/organic astrochemistry" might not be much of a leap from that point.
Chemistry is the middle child of the sciences. It lacks the romantic associations of astronomy, the flamboyant geniuses of physics, the obvious utility of biology. In the minds of the public, it is practical and necessary, but the idea of performing chemical research seems redundant. The periodic table is complete, or at least, it lacks only elements with lifetimes on the scale of femtoseconds, which are hardly relevant to the construction of compounds we encounter in our daily lives. Put together the atoms and you make molecules. When the molecules react, they make other molecules. It doesn't sound very exciting. However, the study of chemistry is the attempt to gain control over the process of making molecules, which is an incredibly ambitious and complex endeavor. Some chemists synthesize organic compounds. Some measure and model energetic, dynamic and kinetic quantities of molecules. Some study on short-lived radicals and ions, others, large biomolecules. In order to achieve the enormous task of mastering molecular creation, it must be broken into smaller portions. I maintain that this end provides all the justification that chemists need. If we don't believe it ourselves, then we can't remind everyone else and we risk being lost from view, like Noyes in the trees.