[extropy-chat] Scientists Confront 'Weird Life' on Other Worlds

[Alejandro Dubrovsky]

On Fri, 2004-05-14 at 13:55 -0700, Robert J. Bradbury wrote:

> Not so fast there Bill -- though there has been some commentary that
> some of the bonds are weaker not all of them are.  Extend the hypothesis
> that "large atoms have weaker bonds" to metallic tungsten, or Titanium
> Carbide or Tantalum carbide or Hafnium carbide -- each of which has extremely
> high melting points (~2-3x higher than various forms of diamond -- in the
> 3000-4000K range...).
> 
Pure diamond melts at 4100K, highest melting point of any substance.

> 
> Not in environments where the ambient temperature is above ~2504 deg K.
> At that temperature SiO2 is a gas just like CO2 is at 195K at normal
> atmospheric pressure.  This analysis is simplistic if larger molecules form
> weaker bonds and yet the boil at higher temperatures...
>   The intermolecular
> bonds are not broken when a compound converts from a solid to a liquid
> to a gas -- yet the interaction capability after these transitions changes
> things significantly. 

CO2 doesn't but SiO2 does i think.  SiO2 in solid does not form a
discrete molecule but is part of a covalent lattice.  Si does not form
double bonds with its oxygen atoms, it forms four single bonds with four
separate oxygens and shares each of those oxygens with another Si atom,
so when it melts, or boils it "breaks".  Molecules of gaseous SiO2 don't
boil away from a solid (i am not a chemist, and one will hopefully step
in to clarify, but this is my best guess).  CO2 on the other hand
remains in its small molecule form loosely held by non-covalent forces
in a solid, so it melts (or sublimes) easily, but each CO2 molecule
survives.

None of this proves that Si cannot be a base for life form to me, but Si
and C react in very different ways.

alejandro