bonding and structure

• Compounds


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

  • Ionic
  • Covalent
  • Metallic
• Ionic bonding


  • Particles are oppositely charged ions
  • Occurs in compounds formed from metals combined with non-metals
• Covalent bonding


  • Particles are atoms which share pairs of electrons
  • Occurs in most non-metallic elements and in compounds of non-metals
• Metallic bonding


  • Particles are atoms which share delocalised electrons
  • Occurs in metallic elements and alloys
• Formation of ionic compounds

  1. Metal atoms lose electrons to become positively charged ions

  2. Non-metal atoms gain electrons to become negatively charged ions
• An ion is an atom that has lost or gained electron(s)
• Ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 gain full outer shell of electrons, so they have the same electronic structure as a noble gas (Group 0 element)
• Electron transfer during the formation of an ionic compound

  • Dot and cross diagram (e.g. for NaCl)
• Ionic compounds


  • Giant structure of ions
  • Held together by strong electrostatic forces of attraction between oppositely charged ions
  • Forces act in every direction since the structure is in 3D
• Ionic compound


  • Sodium chloride (salt)
• Covalent bonding


  Atoms share one or more pairs of electrons
• Small molecules with covalent bonds

  • HCl, H2, O2, Cl2, NH3, CH4
• Polymers


  Large covalently bonded molecules
• Giant covalent structures (macromolecules)

  Many atoms covalently bonded in a lattice structure
• Giant covalent structures


  • Diamond, silicon dioxide
• Metallic bonding


  Positive ions (atoms that have lost electron(s)) and delocalised electrons arranged in a regular pattern

  
• Metallic bonding


  • Delocalised electron system consists of the electrons 'lost' from the atoms to form positive ions
  • Delocalised electrons are free to move through the structure
  • Delocalised electrons are shared through the structure so metallic bonds are strong

  
• 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
  • Based on hexagonal rings of carbon atoms, but may also contain rings with five or seven carbon atoms
• Buckminsterfullerene (C60)


  The first fullerene to be discovered, has a spherical shape
• Carbon nanotubes


  Cylindrical fullerenes with very high length to diameter ratios
• Nanoparticles


  Particles 1-100 nanometers across, containing a few hundred atoms
• Carbon nanotubes


  • Their properties make them useful for nanotechnology, electronics and materials
• Particle sizes


  • Nanoparticles (1-100 nm)
  • Fine particles (PM2.5, 100-2500 nm)
  • Coarse particles (PM10, 1-2.5 μm)
• 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
• 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
• Nanoparticles have different properties to the 'bulk' chemical they're made from


  Due to their high surface area to volume ratio
• Nanoparticles


  • They have a high surface area to volume ratio
  • Smaller quantities may be needed to be effective compared to normal particle sizes
• Uses of nanoparticles


  • Good catalysts
  • Highly selective sensors
  • Stronger, lighter building materials (nanotubes)
  • New cosmetics (no white marks)
  • Lubricant coatings (reduce friction)
  • Small electrical circuits (nanotubes conduct electricity)
• There are some concerns that nanoparticles may be toxic to people and able to enter the brain from the bloodstream
• Non-metal elements have low melting points and boiling points compared to metals.