Bonding + Smart materials

• Metallic bonding


  When metal atoms bond together
• Metals


  • Have giant structures of regularly arranged atoms
  • The electrons from the outer shells of the atoms are delocalised – meaning they are free to move through the whole structure
• Metallic bonds

  Formed by sharing delocalised electrons
• Strength of metallic bond

  Due to the force of attraction between the metal ions (+) and the delocalised electrons (-)
• Metallic properties

  • Conduct electricity - the delocalised electrons carry electrical charge through the structure
  • Conduct heat – the delocalised electrons and closely packed ions transfer energy through the structure by conduction
  • Malleable and ductile - the layers of metal ions are able to slide over each other when hammered or stretched
  • High melting and boiling points – large amounts of energy are needed to break the strong metallic bonds in melting / boiling
• The melting and boiling points increase as you move across any period of the Periodic table, because there are more delocalised electrons increasing the attraction between the ions and the free electrons (stronger bonds)
• Ion


  A charged particle. Has different numbers of protons and electrons
• Positive ion

  Has more protons (+) than electrons (-)
• Negative ion


  Has more electrons (-) than protons (+)
• Ionic bonding


  The bonding between metal and non-metal atoms
• Ionic bonds form


  Electrons transfer from a metal to a non-metal atom so that both atoms achieve full outer shells
• Dot and Cross diagram

  Representation to show ionic bonding
• Covalent bonding


  The bonding between non-metal atoms
• Covalent bonds form


  Atoms share electrons so that both atoms achieve full outer shells
• Single bonds

  • 1 pair of electrons shared
• Double bonds


  • 2 pairs of electrons shared
• Giant ionic structures


  Ionic compounds have giant ionic structures. Ionic lattice – the regular arrangement of the ions in ionic structures
• Properties of giant ionic structures

  • High melting and boiling points – due to the strength of the electrostatic forces between the ions
  • Conduct electricity when dissolved or molten – only then are the ions free to move to carry the charge
• Simple molecular structures


  Consist of a few atoms held together by covalent bonds
• Simple molecular structures

  • Hydrogen
  • Water
  • Carbon dioxide
• Properties of simple molecular structures

  • Low melting and boiling points – due to the weak intermolecular forces between the molecules
  • Do not conduct electricity – no free electrons to carry the electric current
• Giant covalent structures


  Consist of lots of atoms held together by covalent bonds. Arranged into giant lattices, which are extremely strong because of the large number of bonds in the structure
• Giant covalent structures

  • Diamond - each carbon bonded to 4 others
  • Graphite - each carbon bonded to 3 others
• Diamond


  • Does not conduct electricity
  • Used in drill bits, glass cutting, gemstones
• Graphite


  • Conducts electricity – delocalised electrons between layers carries charge
  • Used in pencils and lubricants – layers can slide over each other
• Metal atoms

  Give electrons to non-metal atoms
• Metal atoms


  Become positive ions
• Non-metal atoms


  Become negative ions
• Ionic bond


  Strong electrostatic force of attraction between oppositely charged ions
• Covalent bond

  Forms when two non-metal atoms share a pair of electrons
• Covalent bonds

  • Electrons involved are in the outer shells of the atoms
  • An atom that shares one or more of its electrons will complete its outer shell
• Covalent bonds

  • Strong - a lot of energy is needed to break them
  • Substances with covalent bonds often form molecules with low melting and boiling points
• Intermolecular forces


  Weak forces between molecules
• Covalent bonds


  • Both nuclei are strongly attracted to the shared pair of electrons, so covalent bonds are very strong and require a lot of energy to break
• Electrostatic forces


  Strong forces between oppositely charged ions in a crystal lattice
• Ionic compounds


  Have high melting points and boiling points due to the strong electrostatic forces between ions
• Solid ionic compounds


  Do not conduct electricity because the ions are held firmly in place
• Molten ionic compounds


  Do conduct electricity because the charged ions are free to move
• Solution of ionic compound in water

  Conducts electricity because the ions are free to move
• Covalently bonded substances

  • Simple covalent molecules
  • Giant covalent structures