Reply #43: It's the geometry.

[immoderate]

Now, I forgot more than I know about chemistry, so bear with this. Carbon is unique in that it is an atom of such size and configuration, and its charges balance in such a way, that it can easily form and break compounds that are soluble or immiscible with water, the universal solvent. Water, itself, is also unusual, in that its geometry and chemistry lends itself to dissolving a wide variety of compounds, yet it's molecular polarization prevents if from combining with organic (carbon based) molecules. It's also unusual in that its solid form is less dense than its liquid form. In other words ice floats.

Carbon is indeed unique. While there is a parallel structure in the silicon atom, leading science fiction types to hypothesize a similar silicon based life structure, it (silicon) does not really have the same chemical properties which would allow it to form the complex organic molecules of carbon based life. Some analogous structures (silicones) can be manufactured in the lab, but there is not the chemical mobility to sustain a chemistry of life.

Hi, and welcome to DU!:hi:

--IMM