2.1 - Investigating Structure & Bonding

• how does x-ray diffraction work

  x-rays are directed towards crystal of of substance being studied

  atoms or ions in crystal scatter x-rays producing pattern of diffracted rays that used to be photographed using x-ray film but now are recorded electronically

  diffraction pattern makes it possible to deduce the 3D crystal structure
• types of structure


  giant structures

  simple molecular structures
• giant structures


  crystal structures where all atoms or ions are linked by a network of strong bonding throughout the crystal
• simple molecular Structures


  groups of atoms held by strong covalent bonding within molecules but weak forces of attraction between molecules
• Main types of giant structures

  ionic solids

  giant covalent Solids

  metals
• properties of ionic substances

  high melting & boiling points

  solid at RTP

  conduct electricity when liquid but not when solid

  Soluble in water
• properties of simple covalent (molecular) substances

  low melting & boiling points

  maybe solid but usually liquid or gas at RTP

  don't conduct electricity as liquid or solid

  solubility in water depends on whether hydrogen bonds are formed
• properties of giant covalent substances

  high melting & boiling points

  solid at RTP

  insoluble in water

  don't conduct electricity as liquids or solid
• properties of metallic substances

  high melting &boiling points

  solid at RTP

  insoluble in Water

  conduct electricity as solids and liquids