Bonding

• The three states of matter

  • Solid
  • Liquid
  • Gas

  
• Melting and freezing

  Take place at the melting point
• Boiling and condensing

  Take place at the boiling point
• Particle theory

  Can help to explain melting, boiling, freezing and condensing
• The amount of energy needed to change state

  Depends on the strength of the forces between the particles of the substance
• The nature of the particles involved

  Depends on the type of bonding and the structure of the substance
• The stronger the forces between the particles

  The higher the melting point and boiling point of the substance
• Limitations of the simple particle model include that there are no forces, all particles are represented as spheres, and the spheres are solid
• Ionic compounds

  • Have regular structures (giant ionic lattices) with strong electrostatic forces of attraction in all directions between oppositely charged ions
  • Have high melting and boiling points because a lot of energy is required to break the many strong bonds
  • When melted or dissolved in water, conduct electricity because the ions are free to move and carry current, but can't conduct electricity when solid because the ions are fixed in place
• Substances that consist of small molecules

  • Are usually gases or liquids that have low boiling and melting points
  • Have weak intermolecular forces between the molecules, which are broken in boiling or melting, not the covalent bonds
  • The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points
  • Don't conduct electricity because small molecules do not have an overall electric charge
• Polymers

  • Have very large molecules
  • Atoms in the polymer molecules are linked to other atoms by strong covalent bonds
  • Intermolecular forces between polymer molecules are relatively strong and so these substances are solids at room temperature
• Substances that consist of giant covalent structures

  • Are solids with very high melting points
  • All of the atoms in these structures are linked to other atoms by strong covalent bonds, which must be overcome to melt or boil these substances
• Examples of giant covalent structures

  • Diamond
  • Graphite (forms of carbon)
  • Silicon dioxide (silica)
• Metals


  • Have giant structures of atoms with strong metallic bonding
  • Most metals have high melting and boiling points
  • The layers of atoms in metals are able to slide over each other, so metals can be bent and shaped, which can make them less useful for certain things
• Alloys

  • Are made from 2 or more different types of metals
  • The different sized atoms distort the layers in the structure, making it harder for them to slide over each other, so alloys are harder than pure metals
• Metals as conductors

  • Good conductors of electricity because the delocalised electrons in the metal carry electrical charge through the metal
  • Good conductors of thermal energy because energy is transferred by the delocalised electrons
• Diamond

  Each carbon is joined to 4 other carbons covalently
• Diamond

  • Very hard
  • Has a very high melting point
  • Does not conduct electricity
• Graphite

  Each carbon is covalently bonded to 3 other carbons, forming layers of hexagonal rings which have no covalent bonds between the layers
• Graphite

  • The layers can slide over each other due to no covalent bonds between the layers, but weak intermolecular forces
  • Soft and slippery
• Graphite

  One electron from each carbon atom is delocalised
• Graphite

  • Similar to metals because of its delocalised electrons
  • Can conduct electricity - unlike Diamond, because the delocalised electrons can move
• Graphene

  Single layer of graphite
• Graphene

  • Has properties that make it useful in electronics and composites
  • Very strong because atoms within its layers are very tightly bonded
  • Elastic because the planes of atoms can flex relatively easily without the atoms breaking apart
• Fullerenes


  Molecules of carbon atoms with hollow shapes
• Fullerenes

  • Based on hexagonal rings of carbon atoms, but may also contain rings with five or seven carbon atoms
  • The first fullerene to be discovered was Buckminsterfullerene (C60), which has a spherical shape
• Carbon nanotubes

  Cylindrical fullerenes with very high length to diameter ratios
• Carbon nanotubes

  • Their properties make them useful for nanotechnology, electronics and materials
• Uses of carbon nanotubes and fullerenes

  • Can be used as lubricants, to deliver drugs in the body and catalysts
  • Nanotubes can be used for reinforcing materials, for example tennis rackets
• Nanoparticles

  Particles 1-100 nanometers across, containing a few hundred atoms
• Particle sizes

  • Nanoparticles (1-100 nm)
  • Fine particles (PM2.5, 100-2500 nm)
  • Coarse particles (PM10, 1x10^-5 m - 2.5x10^-6 m)
• Coarse particles are often referred to as dust
• As the side of a cube decreases by a factor of 10

  The surface area to volume ratio increases by a factor of 10
• Fullerenes


  Nanoparticles involve fullerenes
• A nanoparticle has different properties to the 'bulk' chemical it's made from, because of their high surface area to volume ratio
• Smaller quantities of nanoparticles may be needed to be effective than for materials with normal particle sizes
• Nanoparticles

  • High surface area to volume ratio
  • Make good catalysts
  • Can produce highly selective sensors
  • Can make stronger, lighter building materials
  • Used in new cosmetics like sun tan cream and deodorant
  • Used in lubricant coatings to reduce friction
  • Conduct electricity, can be used in small electrical circuits for computers
• There are some concerns that nanoparticles may be toxic to people and able to enter the brain from the bloodstream and cause harm
• Compounds

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

  • Ionic
  • Covalent
  • Metallic