Solid Structures

Understanding Solid Structures

  • A solid structure in chemistry refers to the pattern in which atoms, ions or molecules are arranged in a solid.
  • Most solids are crystalline, meaning they have a regular arrangement of particles.
  • Amorphous solids lack a regular arrangement of particles and don’t possess a defined shape.

Types of Solid Structures

Ionic Structures

  • Ionic structures contain positive and negative ions held together by strong electrostatic forces known as ionic bonds.
  • They possess high melting and boiling points due to their strong ionic bonds.
  • In aqueous solution, or when melted, ionic structures conduct electricity as the ions are free to move.

Metallic Structures

  • Metallic structures consist of positive metal ions surrounded by a ‘sea of delocalised electrons’.
  • This delocalised electron model accounts for many physical properties of metals, such as conductivity and malleability.

Covalent or Network Structures

  • Covalent or network structures include diamond, graphite and silicon dioxide.
  • These compounds consist of a giant lattice of covalently bonded atoms.
  • Covalent structures have high melting and boiling points due to the strong covalent bonds that must be broken.

Molecular Structures

  • Molecular structures consist of simple molecules bound together by weak forces.
  • As these forces are relatively weak, molecular substances usually have low melting and boiling points.

Characterising Solid Structures

  • Analyse the properties of a substance, such as melting and boiling points, to determine its structure.
  • The crystal structure of a compound refers to the order in which the particles are arranged.
  • X-ray crystallography is a practical method to investigate the arrangement of atoms in a crystalline solid.

Understanding Polymorphs

  • Polymorphs are compounds with the same chemical composition but different crystal structures.
  • Different polymorphs can have significantly different physical and chemical properties.