10.0 CARBON AND ITS COMPOUNDS

Carbon is the element of life. It exists in many forms, from the soft graphite in your pencil to the hardest natural diamond. It combines with oxygen to form two oxides—one essential for life (carbon dioxide) and one deadly poison (carbon monoxide). Its compounds, carbonates, are widespread in rocks and shells. And its movement through the environment—the carbon cycle—is fundamental to climate and life on Earth. This chapter explores the fascinating chemistry of this unique element.

10.1 ALLOTROPES OF CARBON

Allotropes are different structural forms of the same element in the same physical state. Carbon has several allotropes, the most common being diamond and graphite. They have identical chemical properties (they both burn in oxygen to form CO₂) but vastly different physical properties because of their different structures.

10.1.1 Diamond

• Structure: Each carbon atom forms four strong covalent bonds with four other carbon atoms in a tetrahedral arrangement. This creates a rigid, three-dimensional giant covalent lattice. There are no free electrons.
• Properties:
  • Extremely hard: The strong, three-dimensional network makes it the hardest natural substance.
  • Very high melting point (~3550°C): Millions of strong covalent bonds must be broken to melt it.
  • Does not conduct electricity: All four outer electrons are used in bonding; no delocalized electrons.
  • High densi