Carbon

Carbon is unique among the elements because its atoms can form an endless variety of molecules with an endless variety of sizes, shapes, and chemical properties. No other element can do that to anywhere near the degree that carbon can. In the evolution of life on Earth, Nature has always been able to "find" just the right carbon compound out of the millions available, to serve just about any required function in the complicated chemistry of living things.

Carbon-containing compounds are called organic compounds, and the study of their properties and reactions is called organic chemistry. The name organic was originally given to those substances that are found in living organisms-plants and animals. As we now know, almost all of the chemical substances in living things are carbon compounds (water and minerals are the obvious exceptions), and the name organic was eventually applied to the chemistry of all carbon compounds, regardless of where they come from.

Until the early nineteenth century, it was believed that organic substances contained a supernatural life force that made them special, and that they were not susceptible to chemical experimentation. But in 1828, a German chemist named Friedrich Wöhler (1800-1882) apparently broke down the mysterious barrier between living and non-living things. By simply heating a non-organic, non-living chemical called ammonium cyanate (NH₄OCN), he converted it into a chemical called urea (H₂N-CO-NH₂), which was known to be a waste product in the urine of mammals and was therefore an "organic" substance. As Wöhler put it, he was amazed to be able to create an organic substance "without benefit of a kidney, a bladder or a dog." What had happened in Wöhler's experiment was that the eight atoms in the ammonium cyanate molecule—two nitrogen atoms, four hydrogen atoms, one oxygen atom, and one carbon atom—simply rearranged themselves into a molecule having a different geometry. In chemical language, the two molecules are isomers of one another.

After Wöhler, chemists boldly synthesized (made artificially) many of the chemical compounds that formerly had been observed only in living things. Today, biochemistry—living chemistry—is one of the most active and productive fields of scientific research. It has taught us more about the processes of life than could ever have been imagined.