Bonding

• Compounds


  Substances in which 2 or more elements are chemically combined
• Types of strong chemical bonds

  • Ionic
  • Covalent
  • Metallic
• Ionic bonding


  • Particles are oppositely charged ions
  • Occurs in compounds formed from metals combined with non-metals
• Covalent bonding


  • Particles are atoms which share pairs of electrons
  • Occurs in most non-metallic elements and in compounds of non-metals
• Metallic bonding


  • Particles are atoms which share delocalised electrons
  • Occurs in metallic elements and alloys
• Formation of ionic bond

  1. Metal atom loses electrons to become positively charged ion

  2. Non-metal atom gains electrons to become negatively charged ion
• An ion is an atom that has lost or gained electron(s)
• Ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 gain full outer shell of electrons, so they have the same electronic structure as a noble gas (Group 0 element)

  
• Electron transfer during ionic compound formation

  • Dot and cross diagram (e.g. for NaCl)
• Ionic compounds


  • Giant structure of ions
  • Held together by strong electrostatic forces of attraction between oppositely charged ions
  • Forces act in every direction since the structure is in 3D
• Covalent bonding


  Atoms share one or more pairs of electrons
• Substances with covalent bonds

  • HCl
  • H2
  • O2
  • Cl2
  • NH3
  • CH4
• Polymers


  Large covalently bonded molecules
• Giant covalent structures (macromolecules)

  • Many atoms covalently bonded in a lattice structure
  • Examples: diamond, silicon dioxide
• Diagrams to show covalent substances

  • Dot and cross
  • Repeat units for polymers using a single line to represent a single bond
  • Ball and stick
  • Two- and three-dimensional diagrams
• Metallic bonding


  • Positive ions (atoms that have lost electron(s)) and delocalised electrons arranged in a regular pattern
  • Delocalised electrons are free to move through the structure
  • Delocalised electrons are shared through the structure so metallic bonds are strong