Atomic & Bonding Quick-Review Notes

Molecular Substances

  • Discrete molecules of non-metals joined by covalent bonds

  • Between molecules: weak intermolecular forces (IMF)

  • Properties

    • Non-conductor (no free moving ions/electrons to carry change)

    • Low melting point, boiling point (little energy needed to overcome these forces)

    • No fixed 3-D structure; usually soft/volatile

Ionic Compounds

  • Particles that make up ionic compounds are called ions

  • They are a metal cation forming an ionic bond with a non-metal anion

  • Bond: ionic bonds (Definition: transfer of electrons from cation to anion)

  • Structure: Cations and anions form a rigid 3D lattice.

  • The ions within the structure are held together by electrostatic attraction.

    The attractive forces are directional.

  • Ionic compounds can conduct electricity, but only when their ions are free to move.

  • This happens when the compound is melted (liquid) or dissolved in water (aqueous), because the ions can move around and carry electric charge.

  • When solid, ionic compounds cannot conduct electricity because their ions are locked in place in a rigid lattice and cannot move.

  • Ionic compounds are hard but brittle – they have a low resistance to impact and so will shatter.

  • When you hit the ionic compound with a hammer, it makes the positive and negative align which causes repulsion and the particles move apart.

Ionic bonding - Chemistry 10

  • Ionic compounds have high melting and boiling points

  • Ionic compounds are solid at room temperature – a lot of energy is required to overcome the ionic bonds

Hardness vs Brittle

  • Hardness is a measure of how easily material can be scratched or indented when pressure is applied

  • Brittle is how much resistance they have to impact and whether they will shatter

  • Brittle is to do with directionality.

Metallic Compounds (Metals / Alloys)

  • Made of metal atoms arranged in a regular 3D pattern (lattice).

  • Alloy: A mixture of two or more metals.

  • Metallic bonds: Attraction between free-moving (delocalized) electrons and positive metal ions.

  • Free electrons move throughout the structure, allowing metals to conduct electricity.

  • Very high melting and boiling points (usually solid at room temperature) because strong metallic bonds need a lot of energy to break.

  • Hard due to the strong 3D structure.

  • Malleable: Can be hammered into sheets.

  • Ductile: Can be stretched into wires.

  • Why malleable/ductile? Layers of atoms can slide over each other without breaking the bonds, so the metal changes shape instead of shattering.