I just learned that 2011 has been designated as the International Year of Chemistry. For a science that has only found its star among the product and pharmaceutical giants, such a declaration is a pretty big deal. Let's be honest, chemistry plays an all-important role in developing the materials we use, but it hasn't captured the public's imagination the way that biology has (I'll admit that Walter White's crystal meth production in Breaking Bad may indicate a changing tide). But now that my final biochemistry grade has been calculated and recorded, honoring the central science is a celebration that I can get on board with.I have always found chemistry to be the most fascinating, if not the most challenging, science I have ever studied. Chemistry and I definitely have a love/hate relationship, but now that I have completed what might be my last chemistry course ever, I'm leaning heavily towards the love side. Learning that all the matter in the universe is governed by the properties of only a handful of different particles is truly an awe-inspiring, if not life-altering, realization. Chemistry doesn't just give meaning to life; it gives meaning to everything. If I dedicate a moment to thinking about that one idea, it absolutely blows me away. Indeed, I have shed a tear while reading my chemistry text, and it's not the kind of tear (rage, desperation, frustration) you may expect.
In my undergraduate chemistry courses, I had trouble grasping some of the advanced concepts simply because I hadn't moved beyond the basics. It's not that I didn't believe them or understand them, it's just that I found the basics far too amazing to simply gloss over in the first two lectures. I didn't have the chance to fully appreciate them before I had to accept them as "oh-yeah-well-duh!"-type truths. I have always thought that atomic structure, the periodic table, principles of chemical bonding, and the properties of water should have their own semester-long course. That course would be taught in an antique parlor somewhere, where students can sit in comfortable chairs under dim lighting, surrounded by candles. There would be group readings, perhaps some chanting, and lots of emotion. It would be something that inspires fits of passion, tears of joy, and students speaking in tongues. To me, chemistry is that amazing.
Maybe it's blasphemy to suggest that chemistry deserves the kind of dramatic and mystical treatment usually reserved for religion. I am among the first to argue that science and religion are incompatible. Scientific inquiry is after all, the antithesis of faith. But chemistry is a discipline rooted in models of reality - the best possible description of that which we cannot actually see. True, models are scientific theory - they are well-tested and supported by independent inquiry, and they offer a sound explanation for natural phenomena. But models have flaws. Models are subject to refinement (plum pudding, anyone?). Indeed, such is the goal of science. To proceed with confidence in the study of chemistry, you must trust the models. You must ignore the nagging worry that somewhere in the world an innovative chemist will soon use the latest technology to debunk, or at least improve upon, the model that you will devote years, a career, your life, to elucidating. It probably won't upend the entire discipline, but it will definitely shake its core. That beautiful eureka moment drives science forward, but it can also break the individual scientist.
Forgive me for being melodramatic. I just read a recent article by Philip Ball in Nature News that reinforced this idea that science is determined to evolve and that nothing is absolutely certain. New techniques are casting doubt on the ABCs of the entire discipline - chemical bonds. No, seriously. The plastic sticks that link the plastic balls in your organic chemistry modeling kit may not actually exist. In fact, the hydrogen bond has already been redefined based on new experimental results that change the idea of electrostatic attraction (I panic - what about protein folding?!). Today's accepted model of the quantum chemical bond is based on interactions between electrons as governed by their wavefunctions, a mathematical tool used to describe the quantum state of a particle. The wavefunction cannot be measured as a one-electron unit, however, because the behavior of each electron depends on the behavior of its neighbors. Now here's the kicker - currently there exists no exact method for computing this correlational energy among electrons, so the description of every quantum chemical bond is at best an approximation.
The existence of a chemical bond also depends on the exact time at which it is characterized. Linus Pauling, the author of the valence-bond description, said that a group of atoms can be considered bonded "when it is convenient for the chemist to consider it as an independent molecular species." Now more than ever this ambiguous definition rings true. Ultra-fast laser spectroscopy, which makes it possible to study molecules on an extremely short time-scale, has produced results suggesting that chemical bonds may not accurately characterize a molecule's structure and reactivity. Moreover, a bond between two atoms embedded within molecule can be difficult to determine - they may simply be held in close proximity by the surrounding atoms. There is also little certainty in deciding which electrons belong to which atoms. The article enforces the idea that molecules are ultimately just a collection of nuclei embedded in a continuous electron cloud. The interactions between atoms - the sticks in our modeling kits - are not hard and fast as we once thought. Despite teaching chemical bonds as a fundamental concept of chemistry for decades, we are witnessing the idea unraveling as new technology and contemporary research challenges our interpretation of the classical work.
What can we do with the theories and models that have been replaced? What becomes of the knowledge that scientists have dedicated their careers to building and that students have toiled to understand? The plum pudding model is actually pretty impressive when you realize that Thompson didn't even know about the atomic nucleus when he came up with the idea in 1904. The nucleus was discovered soon after with Geiger and Marsden's beautiful gold foil experiment in 1909. But Rutherford's planetary model of the atom, a theory borne out of the gold foil experiment, was subsequently improved by Neils Bohr with the development of quantum mechanics. Even the Bohr model has since been invalidated and replaced with the frustratingly complicated atomic orbital model. Though they may seem silly now, these models were not replaced because the science behind them was shoddy or careless. On the contrary, each was revolutionary and derived from elegant experimentation and theory. Scientists can only use the technology available to them to make careful leaps from existing knowledge. These limits to scientific research are better seen in hindsight.
Luckily disproved or refined models do not decay in obsolescence, rather they enrich the discipline. I realized this fact when I found myself able to recall the antecedent atomic models just now. Even though it may not appear on an exam, we are taught the history of chemistry in class because it honors the ground-breaking work of chemists, and it illustrates the way in which science grows from existing knowledge. Refinement of existing theories is proof that science works. Classical research is meaningful, even if it is no longer useful. As Ronald Hoffmann of Cornell University says of the hotly debated valence bond and molecular orbital theories, "discarding any one of the two theories undermines the intellectual heritage of chemistry." Honoring past research gives value to modern science and motivates scientists who know that their discoveries may ultimately be bested. The beauty of science is that it is humble in the present, constantly striving to improve itself, while being deeply reverent of the past.
References: Ball, P. (2011). "Beyond the bond." Nature 469(7328): 26-28.
