Covalent Bonds and the Properties of Covalent Compounds

  • Definition: Intramolecular forces hold atoms together within a molecule.

  • Types of Bonds: Includes covalent (polar and nonpolar), ionic, and metallic bonds.

  • Origin: Result from differences in electronegativity of atoms.

  • Impact: The type and strength of these forces affect physical properties.

Comparison of Intramolecular Forces

  • Ionic Bonding:

    • Model: Cation-anion interaction.

    • Attraction: Electrostatic attraction.

    • Energy: 400−4000 kJ/mol400-4000 \, kJ/mol.

    • Example: Sodium chloride (NaClNaCl).

  • Covalent Bonding:

    • Model: Nuclei sharing electron pairs.

    • Attraction: Between nuclei and shared electrons.

    • Energy: 150−1100 kJ/mol150-1100 \, kJ/mol.

    • Example: Molecular hydrogen (H−HH-H).

  • Metallic Bonding:

    • Model: Cations surrounded by delocalized electrons.

    • Attraction: Between cations and mobile electrons.

    • Energy: 75−1000 kJ/mol75-1000 \, kJ/mol.

    • Example: Iron (FeFe).

Principles of Covalent Bonding

  • Covalent Bonds: Strong bonds formed by sharing electrons.

  • Classes:

    • Nonpolar Covalent: Equal sharing of electrons (e.g., Cl−ClCl-Cl).

    • Polar Covalent: Unequal sharing, resulting in partial charges (e.g., H−ClH-Cl).

    • Contrast with Ionic: Ionic bonds involve complete electron transfer.

Covalent Substances

  • Types:

    • Simple Covalent (Molecular): Includes gases and small molecular solids.

    • Covalent Lattice (Giant Covalent): Large, strong network structures.

Simple Covalent Molecules

  • Composition: Few atoms held by strong covalent bonds (e.g., CO2CO_2, H2OH_2O).

  • Properties:

    • Low melting/boiling points due to weak intermolecular forces.

    • Non-conductive due to lack of free electrons.

Giant Covalent Structures

  • Definition: Consist of many non-metal atoms in a strong lattice.

  • Examples: Diamond (rigid), Graphite (layers), Silica (SiO2SiO_2).

  • Properties:

    • High melting points due to strong bonds.

    • Variable conductivity: Diamond (non-conductive), Graphite (conductive).

Carbon and Covalency

  • Versatility: Carbon's ability to form four covalent bonds.

  • Catenation: Forms long chains, branched, and ring structures.

  • Bond Diversity: Can form single, double, and triple bonds, contributing to molecular diversity.

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