|MadSci Network: Chemistry|
A diamond crystal is a single covalently-bonded carbon molecule. The largest one found to date was named the Cullinan, massing 621.2 grams. Cured epoxy resin, crosslinked silicone, cured polyester resin... almost any extensively crosslinked thermoset resin approximates to one big molecule.
DNA unravels to macroscopic lengths, but it is too thin to be seen without being imaged by an electron or scanning tunneling microscope.
If you relax the requirement for covalent bonding, things get much bigger. How covalent is elemental silicon? Single crystal ultrapure boules are routinely Czochralski grown a full foot wide and several feet long. Simple ionic crystals are one big "molecule." How big is a salt deposit? If you settle for mere hydrogen bonding, you have the oceans.
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