Carbon -- Element of the Day

October 5, 2001

Elemental carbon comes in several forms

diamond, crystalline

• occurs naturally, mined
• also made synthetically (both gem and industrial diamonds)
  • seldom realized-- diamonds became popular gemstone only after 1920
    • Victorian era rings were sapphires, pearls, ruby, emeralds, garnets
    • Diamonds were fairly drab-- cut glass generally looked better
    • Cutting and polishing diamonds is very difficult
      • to look brilliant, diamonds need elaborate cutting
      • many more facets than other gems
      • wasn't practiced until early 1900's
    • Older diamonds were often used as found
      • show well developed crystal faces,
      • interesting but more of a novelty than a great gemstone

Also one of the great economic stories

• cornering market, driving out competition (any means)
• driving up prices by artificially withdrawing supply
• creating a demand (engagement rings) where none existed before

diamond is also important industrial material

• hardest common material,
• great in saw blades to cut concrete and steel
• great in polishing compounds
• new: we can now deposit thin layers of diamond
  • diamond-like to be honest
  • makes very hard surfaces, cutting edges

• History of Diamonds
• The Hope Diamond, for those of you who think big

Graphite, also crystalline carbon

• mined (rare to find good deposits)
  • see the book: Pencil (an interesting history of a simple object)
  • Henry David Thoreau, earned his living as a pencil maker
    • orginal notes incorrectly said Walt Whitman
    • Thoreau's father owned the factory
• weakly bound layers of carbon
• soft (pencil leads of graphite are too soft-- add clay)
• lubricant rather than an abrasive

• Pencils
• crystal form of diamond, graphite

Amorphous forms of Carbon

• charcoal, soot or carbon black
• auto tires have lots of Carbon Black (soot)

C60 and related compounds

• Buckyballs
• All synthetic, very specialized materials
• click here for Buckball picture and information

But most interest in Carbon is not in the elemental form or in the small molecules like CO, CO₂ , and CH₄ .

• Nearly unique--
• Carbon forms bonds strongly to other carbons
  • Provides a backbone of C-atoms
  • Nearly unlimited range of possibilities
  • bond energies are in a good neighborhood
    • stong enough to be stable
    • weak enough for possibilities (say in living organisms)
• Comparison:
  • Sand SiO₂ forms Si-O-Si-O ... structures
  • but nature provides no Si-Si-Si structures

• Backbone of C's leaves a lot of electrons for other bonds
  • H- is most common
  • if only H, these are hydrocarbons
  • but a half dozen other elements are important
    • O- oxygen
    • N- nitrogen
    • Cl- chlorine (or other halogens)
    • S- sulfur
    • P- phosphorus

• One case C-C-C-C- O - H
  • -O-H is an alcohol group
  • all alcohols have similar chemistry and properties
    • size of C-chain modifies the properties
  • alcohols tend to dissolve in water, hydrocarbons don't
    • biologically important-- chemically we are mostly water
    • medicinal, biologic effect usually needs water solubility
• where on the C chain also affects properties
  • we can produce 50 or so different alcohols

• Another case C-C-O-C-C (link by an oxygen)
  • ethers ... different properties
• Can have combinations C-C-O-C-OH

Organic Chemistry

• set of functional groups (fix the chemistry)
• a range of backbones
  • fix solubility, solid-vs-liquid
  • modify properties
• Tailor made materials, fine tuning properties....

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