Bonding in Carbon: The Covalent Bond
Carbon (atomic number 6) has 4 electrons in its outermost shell. To achieve a stable noble gas configuration, it does not gain or lose 4 electrons because doing so would require immense energy and create highly unstable ions. Instead, it shares its valence electrons with other atoms. Bonds formed by the sharing of electron pairs are called covalent bonds. These molecules have strong bonds within the molecule but weak intermolecular forces, giving them low melting and boiling points.
The Versatile Nature of Carbon
Two key properties allow carbon to form millions of distinct compounds:
- Catenation: Carbon has the unique ability to form bonds with other carbon atoms, giving rise to long chains, branched chains, or closed rings. This property is stronger in carbon than in any other element.
- Tetravalency: Since carbon has a valency of 4, it is capable of bonding with four other atoms of carbon or atoms of other monovalent elements (like Hydrogen, Oxygen, Nitrogen, or Halogens).
Saturated and Unsaturated Carbon Compounds
Hydrocarbons containing only single bonds between carbon atoms are called saturated hydrocarbons, or Alkanes (general formula: CnH2n+2). Hydrocarbons containing one or more double or triple bonds between carbon atoms are unsaturated hydrocarbons, known as Alkenes (CnH2n) and Alkynes (CnH2n-2), respectively. Unsaturated compounds are generally more reactive than saturated ones.
Functional Groups and Homologous Series
In a hydrocarbon chain, one or more hydrogen atoms can be replaced by other atoms or groups of atoms, called functional groups (e.g., Alcohols -OH, Aldehydes -CHO, Carboxylic acids -COOH). A homologous series is a family of organic compounds with the same functional group and similar chemical properties, where successive members differ by a -CH₂ unit.
Important Compounds: Ethanol and Ethanoic Acid
Ethanol (Ethyl Alcohol, C₂H₅OH): A liquid at room temperature, it is the active ingredient in alcoholic drinks and a good solvent used in medicines like tinctures and cough syrups. Ethanoic Acid (Acetic Acid, CH₃COOH): A 5-8% solution of ethanoic acid in water is called vinegar. It is widely used as a preservative in pickles. When pure, it freezes during winters, earning the name glacial acetic acid.