Bonding, Structure and the Properties of matter

• Ionic bonding


  Electrostatic attraction between positive and negative ions. It is a relatively strong attraction.
• How ionic compounds are held together

  1. They are held together in a giant lattice

  2. It's a regular structure that extends in all directions in a substance

  3. Electrostatic attraction between positive and negative ions holds the structure together
• Properties of ionic substances

  • High melting and boiling point (strong electrostatic forces between oppositely charged ions)
  • Do not conduct electricity when solid (ions in fixed positions)
  • Conduct when molten or dissolved in water - ions are free to move
• Examples of positive ions


  • Na+
  • Mg2+
  • Al3+
  • Ca2+
  • Rb+
• Examples of negative ions (anions)


  • Cl−
  • Br−
  • SO4

  2−

  • NO3

  −

  • OH−
• Ionic compounds are electrically neutral, i.e. positive and negative charges balance each other
• How ionic compounds are formed (using MgO as an example)

  1. Reaction of a metal with a non-metal

  2. Electron transfer occurs - metal gives away its outer shell electrons to non-metal

  3. Mg is in Group II, so has 2 available outer shell electrons

  4. O is in Group VI, so can accept 2 electrons to get a full outer shell configuration

  5. Mg becomes Mg2+ and O becomes O2− (oxide)
• Covalent bond


  Shared pair of electrons between two atoms
• Properties of simple molecular covalent substances

  • Do not conduct electricity (no ions)
  • Small molecules
  • Weak intermolecular forces, therefore low melting and boiling points
• Intermolecular forces


  They increase as the mass/size of the molecule increases, causing melting/boiling points to increase as well (more energy needed to overcome these forces)
• Polymers


  Very large molecules (>100s, 1000s of atoms) with atoms linked by covalent bonds
• Thermosoftening polymers


  Special type of polymers; they melt/soften when heated. There are no bonds between polymer chains. Strong intermolecular forces ensure that the structure is solid at room temperature. These forces are overcome with heating - polymer melts.
• Giant covalent substances


  • Solids, atoms covalently bonded together in a giant lattice
  • High melting/boiling points – strong covalent bonds
  • Mostly don't conduct electricity (no delocalised e−)
  • Examples: diamond, graphite, silicon dioxide