Get Your Carbs Here!

A single blogpost will just not cut it for carbon, the 6th element. There are so many interesting little sub-topics to cover like diamonds, graphite, buckyballs, and nanotubes. But that wouldn't even begin to touch on compounds, e.g., the hydrocarbons, which give us energy and which also fuel human conflicts past, present and future. And then there's carbon combining with other elements that I haven't reached yet- elements like nitrogen and oxygen: hello, CO₂ anyone? Of course that wouldn't get us to carbohydrates or even amino acids, let alone to proteins and things that make up living creatures. I'll probably end up doing several blog posts on carbon, but also keep moving ahead.

Many chemists fall so in love with carbon that they never get past it. Those chemists are called organic chemists. To help understand why carbon is so special, consider a "carbo-centric" version of the periodic table which any Organiker should love:

original

That chart used to be standard fare at German universities (and let's face it: until the end of WW II, the Germans were organic chemistry). Notice how carbon sits dead center in a row of nine elements, having an equal number of elements to its right and to its left. Here is that first row or period again, pulled out of the chart:

    He     Li    Be     B      C      N     O     F     Ne

Carbon is the first element beyond helium that is found (practically) pure in the elemental state. In general, when commingling, elements tend to gain or lose valence electrons to resemble the nearest noble gas: elements to the left of carbon (e.g., Li⁺, Be²⁺) achieve the electronic nobility of helium by doffing one or two electrons respectively; elements to the right (O^2-, F^-) achieve the nearest noble gas configuration of neon by gaining one or two electrons; elements in the middle (B, C, N) tend to neither completely gain nor to lose electrons, but rather, to share electrons with other elements. These tendencies are a consequence of electronegativity. Carbon also forms so many compounds because of catenation. Catenation is just a fancy latinate word for "linking together"-something that carbon is good at doing, especially with itself.

Returning to the carbo-centric periodic table above, note that there is a similar row or period centered around silicon:

    Ne    Na     Mg    Al     Si      P      S      Cl    Ar

One might ask whether a similarly rich silicon chemistry exists. The short answer is no, because silicon can't self-catenate like carbon can.  Silicone polymers require the insertion of one oxygen atom between silicon "monomers." But some might argue that silicon-based life, created in our own image, has just begun to evolve--it just finds our oxygen-rich environment too hostile.