Thursday, June 20, 2013

The carbon silicon saga - I

Carbon is the backbone of life on earth. If not for carbon, there would be no life. Why is carbon so versatile? As you know, atoms have electrons orbiting around their nucleus. Each orbit can hold a specific amount of electrons. In nature, atoms love to have their orbital full, since that makes them most stable. Carbon, element no. 6, has in its outermost orbital 4 electrons, and can accommodate 4 more. So it seeks electrons from any neighbouring atoms it can find and in its zest to find electrons, it bonds with virtually anything ('bonding' is chemistry lingo for sharing electrons). This promiscuity makes carbon such a life giver. Carbon can bond with upto four other atoms and is not picky about the direction in which it wants to bond. This allows carbon to build a complex chain of even three-dimensional webs of molecules. Unlike many other elements, carbon also shares electrons (Many elements steal electrons and fill up their orbitals). This sharing nature of carbon also makes it stable. With such gentle and accommodating nature, carbon can form amino acids, which forms proteins, which ultimately form life.
Is there no other element like carbon then? Well there is and it is a big hit among people looking for life in outer space and writing science fiction. It's eight elements away, sits right below carbon on the periodic table and is called Silicon. Silicon too has vacancies for four electrons in its outermost orbital and leaves it in the same predicament as carbon. But unfortunately (for sci-fi fans at least) silicon cannot pull some nifty tricks which carbon can. One for example is; carbon combines with oxygen, forming carbon-di-oxide, which is a gas and is easily shuttled around the body. Silicon would form Silicon di oxide, which other than being closely related to sand is a solid. Since solids stick together, its difficult for them to get in and out of cells when needed. Silica, does not even dissolve in water and that makes nutrient transport impossible. If the above reason does not satisfy you, then how about this- Since Silicon has more protons-neutrons and electron than carbon it is more bulky than carbon. The lean, thin carbon can contort, itself into ringed molecules we call sugars. Rings are in state of high tension and so pack in a lot of energy and the bulky silicon is just not supple enough to bend into the right position to form rings. For reasons like this and some more, carbon has made itself irreplaceable in the story of life.
Just like the carbon has formed the backbone of life, Silicon too has its share in our life. Today it forms the backbone of our digital world. Without silicon, you probably would not be reading this. Silicon to digital world is what carbon is to life. No computers, no smart phones and no blogger without silicon. But silicon a few years ago nearly lost this title to the element sitting right beneath it in the periodic table- Germanium. That story in tomorrows post.

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