14.4A: Graphite and Diamond - Structure and Properties
- Page ID
- 34175
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Introduction
- There are more compounds of carbon than of any other element except hydrogen. Most of carbon chemistry is handled in different courses (organic and biochemistry).
- There are no compounds containing anything like C4+ but some carbides contain a species approximating C4-.
- There are transient ionic species: carbonium ions such as F3C+, and carbanions such as (NC)3C-. Notice the attached groups which would help to stabilize these species.
- Transient divalent carbon occurs in carbenes, R2C:
- The strong C—C single bond and the ability to form double, C=C, and triple, CºC, bonds contributes to the huge versatility of carbon.
The Chemistry and Physical Properties of Diamond Graphite and the Fullerenes
Carbides
These come in three general types:
Ionic carbides are formed by elements of groups 1, 2 and aluminum. The actual for of the carbon varies, for example, aluminum carbide, based on its hydrolysis product seems to contain "C4-" units:
\[\ce{Al4C3 + 6H2O -> 2Al(OH)3 + 3CH4}\]
but calcium carbide seems to contain [CºC]2- units:
\[\ce{CaC + 2H2O -> Ca(OH)2 + HCºH}\]
Interstitial carbides are compounds of the transition metals with metallic properties and the C in tetrahedral holes in the metal atom lattice. The best known example is the extremely hard tungsten carbide, WC, used in cutting tools.
Covalent carbides include B4C3 and SiC (carborundum - an abrasive with a diamond-like structure)