bonding, structure and properties of matter

• solids cannot be compressed because the particles are closely packed together with almost no gaps between the particles.
• alloys are harder than pure metals because the atoms in it are different sizes, meaning the layer arrangement is disrupted and so atoms cannot slide over each other (which is what allows metals to be bent and shaped)
• knowledge of bonding and structure are used to engineer new materials with desirable properties
• Metals are good conductors of electricity because the delocalised electrons in the metal carry electrical charge through the metal.
• • melting and freezing take place at the melting point
  • boiling and condensing take place at the boiling point
• ionic bonds:

  • occurs between negative non-metal ions and positive metal ions
  • where the electrons are transferred from the metal to the non-metal
  • and the oppositely charged ions have strong electrostatic forces of attraction bonding them together
• anion = negative ions

  cations = positive ions
• describing ionic bonding, state:

  • how many electrons the metal loses
  • the resulting charge of the metal ion
  • electron are transferred from the metal to the non-metal
  • how many electrons the non-metal gains
  • the resulting charge of the non-metal ion
  • that the oppositely charged ions are held together by strong electrostatic forces of attraction in ionic bonding
• ionic structures form giant lattice structures:

  • regular arrangement
  • where positive and negative ions alternate, and are closely packed together
  • strong electrostatic forces of attraction hold positive metal ions and negative non-metal ions together to form a lattice structure
  • the electrostatic forces of attraction are strong and act in all directions
  • and while there are ions, the charges cancel each other out so the lattice has no overall charge
• representing bond structures --

  • dot-and-cross diagrams:
  • advantage - easy to see where electrons have been transferred from and to
  • disadvantage - doesn't represent 3D structures (eg giant ionic lattices) and doesn't tell anything about the shape of the molecule
  • 2D stick diagrams:
  • disadvantage - cannot tell which atom the electron came from, doesn't given any information of electrons that are not involved in the bond (for covalent bonds), 2D stick diagrams do not give accurate information regarding the shape of the molecule
• representing bond structures --

  • 3D stick diagrams:
  • advantage - shows the shape of the molecule
  • ball and stick diagrams (ionic lattices):
  • advantage - clearly shows the structure between different ions
  • disadvantage - ions are seen as far apart, when in reality they are very closely packed together, only shows a small part of the giant lattice
  • space filling diagrams (ionic):
  • advantage - clearly shows how closely together the ions are
  • disadvantage - difficult to see the three dimensional structure, only shows a small part of the giant lattice so mistaken size of the structure
• an ionic compound is a giant structure of ions which are held together by electrostatic forces of attraction
• covalent bonds:

  • form when two non-metal atoms share electrons to obtain a full outer shell
• ionic bond properties:

  • ionic bonds have high melting and boiling points due to the strong electrostatic forces of attraction in all directions between oppositely charged ions, meaning lots of energy is required to overcome the forces and break the many strong bonds
  • can conduct electricity when dissolved in water or melted because the ions are free to move and so charge can flow (current).
  • They cannot conduct electricity when solid because the ions are fixed in their lattice structure
• small molecules (simple covalent) properties:

  • simple covalent molecules have strong covalent bond but weak intermolecular forces. It is these intermolecular forces that need to be overcome when a substance melts or boils (not the covalent bond) so substances made from small molecules have low melting and boiling points
  • intermolecular forces increase with size of the molecules, so larger molecules have higher melting and boiling points
  • substances consisting of small molecules cannot conduct electricity because the molecules do not have an overall electric charge.
• polymers:

  • polymers have very large molecules
  • the atoms in the polymer molecules are linked to other atoms by strong covalent bonds
  • the intermolecular forces between polymer molecules are relatively strong and so these substances are solids at room temperature
• giant covalent structures:

  • substances that consist of giant covalent structures are solids with very high melting points
  • all the atoms in these structure are linked to other atoms by strong covalent bonds
  • these many strong bonds must be overcome to melt or boil these substances
• properties of metals and alloys:

  • metals have giant structures of atoms with strong metallic bonds
  • this means that most metals have high melting and boiling points (bonds need to be overcome)
  • in pure metals, the atoms are arranged in layer which allow them to slide over each other, making pure metals malleable and able to be bent and shaped. Pure metals are too soft for many uses and so mixed with other elements to make them stronger.
• metals as conductors:

  • metals are good conductors of electricity because the delocalised electrons in the metal carry electrical charge through the metal
  • metals are good conductors of thermal energy because energy is transferred by the delocalised electrons
• diamond --

  • in diamond, each carbon atom is covalently bonded to 4 other carbon atoms which forms a tetrahedron
  • diamond is an allotrope of carbon
  • diamond is a giant covalent structure
  • so diamond is very hard, cannot conduct electricity and has a very high melting point
• diamond -- cannot conduct electricity:

  • all the outer shells of carbon in diamond are held in the covalent bonds around each carbon atom, so there are no freely moving charged particles to carry a current. This means diamond cannot conduct electricity.
• diamond -- very high melting point:

  • diamond has a very high melting point because there are many strong covalent bonds in all directions that extend into a lattice. This means a lot of energy is required to overcome the forces and break the lattice, so diamond has a high melting point
• diamond -- hard:

  • diamond is hard because of the rigid lattice structure of carbon atoms held together by covalent bonds.
• graphite --

  • in graphite, each carbon atoms forms three covalent bonds with three other carbon atoms, forming layers of hexagonal rings which have no covalent bonds between the layers
  • in graphite, one electron from each carbon atom is delocalised
  • there are strong covalent bonds between the carbon atoms, but weak intermolecular forces of attraction between the layers
• graphite -- conducts electricity and heat:

  • in graphite, one electron from each carbon atom is delocalised
  • these electrons are free to move and carry a charge
  • so graphite can conduct electricity
  • and these electrons can move through the graphite layers
  • making graphite thermally conductive
  • so graphite can conduct heat
• graphite -- soft and slippery:

  • graphite's structure consists of layers
  • and the layers in graphite have weak intermolecular forces of attraction
  • which allows them to slide over each other, making graphite soft and slippery
• graphite -- high melting point:

  • graphite has many strong covalent bonds
  • that need to be broken to break the solid hexagonal ring layers in graphite
  • and a lot of energy is required to overcome these strong bonds meaning graphite has a high melting point
• graphite's structure is similar the the structure of metals because both have delocalised electrons
• graphene is a single layer of graphite, and has properties that make it useful in electronics and composites
• graphene --

  • is extremely strong due to its unbroken pattern and strong covalent bonds between the carbon atoms, but very light because it is only one thin layer of carbon atoms
  • it can conduct electricity because of the free, delocalised electrons that can move along its surface allowing it to conduct electricity
  • it is flexible because the strong covalent bonds between the carbon atoms are very flexible
  • it is transparent
• fullerenes are molecules of carbon atoms with hollow shapes.
• Buckminsterfullerene (C60) was the first fullerene to be discovered, and it has a spherical shape
• The structure of fullerenes is based on hexagonal rings of carbon atoms but they may also contain rings with five or seven carbon atoms.
• carbon nanotubes are cylindrical fullerenes with very high length to diameter ratios. Their properties make them useful for nanotechnology, electronics and materials