Chemical Bonding

This note covers ionic, covalent, and metallic bonding, along with the structure and properties of materials, including elements, compounds, mixtures, and alloys, and compares structures like diamond and graphite.

1. Ionic Bonding
  • 🔹 Formation of Ions:
    • 🔹 Metals lose electrons to form positive ions (cations), e.g., Na → Na⁺.
    • 🔹 Non-metals gain electrons to form negative ions (anions), e.g., Cl + e⁻ → Cl⁻.
    • 🔹 Both achieve noble gas electronic configuration (duplet for H, He; octet for others).
  • 🔹 Ionic Bond Formation:
    • 🔹 Electrons transfer from metal to non-metal, e.g., NaCl (Na⁺Cl⁻), MgCl₂ (Mg²⁺Cl⁻₂).
    • 🔹 Strong electrostatic attraction between oppositely charged ions forms the bond.
  • 🔹 Structure:

    🔹 Giant ionic lattice: 3D repeating arrangement of cations and anions, e.g., NaCl has alternating Na⁺ and Cl⁻.

  • 🔹 Physical Properties:
    • 🔹 High melting/boiling points due to strong ionic bonds.
    • 🔹 Hard but brittle: shifting layers aligns like charges, causing repulsion.
    • 🔹 Conduct electricity when molten or aqueous (ions free to move).
    • 🔹 Usually soluble in water due to ion-dipole interactions.
2. Covalent Bonding
  • 🔹 Formation:
    • 🔹 Non-metal atoms share electron pairs to achieve noble gas configuration.
    • 🔹 Single bond: 1 pair (e.g., H₂), double: 2 pairs (e.g., O₂), triple: 3 pairs (e.g., N₂).
  • 🔹 Examples:
    • 🔹 Simple molecules: H₂, O₂, CO₂, CH₄, H₂O.
    • 🔹 Giant covalent: diamond, graphite, SiO₂.
  • 🔹 Electron Arrangement:

    🔹 Deduced using valency and dot-and-cross diagrams, e.g., CH₄ has 4 single C-H bonds.

  • 🔹 Physical Properties:
    • 🔹 Simple Molecular:
      • 🔹 Low melting/boiling points (weak intermolecular forces).
      • 🔹 Non-conductors.
      • 🔹 Often insoluble in water (e.g., CH₄).
    • 🔹 Giant Covalent:
      • 🔹 Very high melting/boiling points.
      • 🔹 Hard (except graphite).
      • 🔹 Mostly non-conductors (except graphite due to delocalized electrons).
3. Metallic Bonding
  • 🔹 Description:
    • 🔹 Lattice of positive metal ions in a sea of delocalized electrons.
    • 🔹 Metallic bond: attraction between positive ions and delocalized electrons.
  • 🔹 Properties:
    • 🔹 High melting/boiling points due to strong metallic bonds.
    • 🔹 Good conductors: mobile electrons carry charge.
    • 🔹 Malleable/ductile: ion layers slide without breaking bonds.
4. Structure and Properties of Materials
  • 🔹 Elements, Compounds, Mixtures:
    • 🔹 Element: One type of atom, e.g., Fe, O₂.
    • 🔹 Compound: Atoms chemically bonded in a fixed ratio, e.g., H₂O, NaCl.
    • 🔹 Mixture: Physical combination, no fixed ratio, separable by physical means, e.g., air, saltwater.
  • 🔹 Alloys:
    • 🔹 Mixture of a metal with other elements, e.g., brass (Cu + Zn), stainless steel (Fe + Cr, Ni).
    • 🔹 Different-sized atoms disrupt the lattice, making alloys stronger, harder, less malleable than pure metals.
  • 🔹 Diamond vs. Graphite:
    • 🔹 Diamond: Each C atom bonded to 4 others in a 3D network; very hard, non-conductor (no free electrons).
    • 🔹 Graphite: Each C atom bonded to 3 others in layers; soft, conducts electricity (delocalized electrons in layers).
  • 🔹 Ionic:
    • 🔹 High melting/boiling points.
    • 🔹 Conduct when molten or aqueous.
    • 🔹 Brittle.
  • 🔹 Simple Covalent:
    • 🔹 Low melting/boiling points.
    • 🔹 Non-conductors.
    • 🔹 Often insoluble in water.
  • 🔹 Giant Covalent:
    • 🔹 High melting/boiling points.
    • 🔹 Hard (diamond) or slippery (graphite).
    • 🔹 Mostly non-conductors.
  • 🔹 Metallic:
    • 🔹 High melting/boiling points.
    • 🔹 Conductive.
    • 🔹 Malleable/ductile.

  • ⚠️ Thinking ionic compounds conduct electricity in solid state—they conduct only when molten or aqueous.
  • ⚠️ Assuming all covalent substances are soft—giant covalent structures like diamond are extremely hard.
  • ⚠️ Confusing metallic bonding with ionic bonding—metallic bonds involve delocalized electrons, not ion pairs.
  • ⚠️ Believing alloys are compounds—alloys are mixtures with no fixed chemical ratio.

  • 👉 Describe ion formation using electron transfer and noble gas configurations.
  • 👉 Draw dot-and-cross diagrams for covalent molecules like CH₄ or O₂.
  • 👉 Explain conductivity differences: ionic (molten/aqueous), metallic (always), covalent (rarely, except graphite).
  • 👉 Compare diamond and graphite structures and link to properties.
  • 👉 Differentiate elements, compounds, and mixtures with examples.

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