Topic 1 - Archived

• Metallic Bonding is:

  A regular arrangement of positively charged metal ions, surrounded by a 'seas' of free outer shell electrons.

  The bonds occur as a result of the forces of attraction between the 'sea' of negative electrons and the positive ions.
• Positive ions do not touch in metallic bonding
• In metallic bonding, the 'sea' of outer electrons acts like glue holding the ions together
• Metals conduct heat as the positive ions are close together and can easily pass the vibration of hot particles from one particle to the next particle.

  Also, the free electrons can move faster as they are heated and transfer the heat from hot to cold throughout the metal.
• Metals have high melting points due to strong metallic bonds.

  More electrons in the sea of outer shell electrons = increase in metallic bond strength = melting point increases
• Metals conduct electricity because the sea of free outer shell electrons is free to move when voltage is applied. The sea moves towards the positive potential.
• Metals are malleable. This means that they can be shaped because of their regular arrangement.
• Metals are ductile. This means that it can be drawn/stretched into wires
• Metals are malleable and ductile because when a force is applied to the metal the layers of ions can slide over each other. The free electrons also act as a lubricant.
• Ionic bonding occurs between metals and non-metals
• in ionic bonding, electrons in the outer shell of the metal atom are transferred to the non-metal atom

  • Metal atoms lose electrons to form positively charged ions.
  • Non-metal atoms gain electrons to form negatively charged ions.
• Electron transfer during the formation of ionic compounds can be represented by a dot and cross diagram.
• The ionic bond is the force of attraction between oppositely charged ions. All ionic compounds have a giant structure - "3D"
• Ionic structures:

  • cannot conduct electricity when solid
  • can when molten (melted) or in solution (dissolved in water)

  Reason: In a solid ions cannot move.

  When molten/in solution ions can move

  Only ionic compounds do this

  The electricity is conducted by moving ions, not free electrons
• Ionic structures have high melting points because ionic bonds are very strong. A large amount of heat/energy is required to break all the ionic bonds in the giant structure.
• In ionic structures, the greater the charges on the ions, the stronger the ionic bonding between ions. This means more energy is needed to overcome the bonding and the melting point increases.
• Covalent bonding occurs between atoms of non-metals. Pair of electrons are shared in the outer shells of the atoms to obtain a full outer shell.
• There are two types of covalent structures:

  • Simple covalent structures
  • Giant covalent structures
• A single covalent bond is a shared pair of electrons. This means each atoms in the covalent bond donates one electron.
• A double covalent bond is a two shared pair of electrons. This means that each atom in the covalent bond donates 2 electrons.
• Simple covalent molecules have low boiling points and low density (usually gases) because there are weak forces of attraction between the molecules (intermolecular) are broken during boiling. The strong covalent bonds are not.
• Simple covalent molecules do not conduct electricity because there are no free electrons or ions to move.
• Giant covalent structures contain many atoms joined together in a regular arrangement by a very large number of covalent bonds. The structures are not simple molecules.
• Diamond has high melting and boiling points - each carbon atom has four strong covalent bonds in all directions (tetrahedral shape) in the giant structure. This strong covalent bonds have to be broken to melt/boil
• Diamond does not conduct electricity - no free electrons available to move because all of the electrons in the outer shell are used in strong covalent bonds
• Diamond is used in drill bits and glass cutting as its very strong and hard
• Diamond is used in jewellery as it is transparent and crystalline
• Graphite has high melting and boiling points - each carbon atom has three strong covalent bonds in all directions (hexagonal shape) in the giant structure. These strong covalent bonds have to be broken to melt/boil
• Graphite does conduct electricity - each carbon atom has one free electron available to move because only three electrons are used in strong covalent bonds
• Graphite is used in pencils and lubricants as there are weak forces of attraction between the flat layers, so the layers easily slide over each other
• Graphite is used in electrodes as it has a high melting point and conducts electricity
• Graphene is a single layer of graphite. As it only has one layer, there are no longer weak forces of attraction between layers, so it is strong and no longer soft and slippery
• In graphene, each carbon atom is still bonded to 3 other carbons within the layer, meaning one electron becomes delocalised so graphene does conduct electricity
• Fullerenes


  Cages and tubes with different numbers of carbon atoms
• Nanotubes are graphene layers that have been rolled into a tube
• Nanotubes conduct electricity
• Nanotubes are extremely strong
• Smart materials


  Materials with properties that change reversibly with a change in the surroundings or environment, such as light or temperature.
• Thermochromic

  Pigments that change colour reversibly due to temperature
• Photochromic


  Pigments that change colour reversibly due to light intensity