Bonding structure and properties

• compounds


  substances in which 2 or more elements are chemically combined
• types of strong chemical bonds

  ionic - the bonding present in ionic compounds

  metallic - the bonding present in metals

  covalent - the bonding present in giant covalent structures and simple covalent molecules
• chemical bonds

  type of bonding accounts for many of the physical and chemical properties of the compound / molecule
• Ionic compounds


  bonding occurs between metals and non mentals

  ionic bonds are electrostatic attractions between oppositely charged ions

  the ions form a giant ionic lattice

  electrons in the outer shell of the metal are transferred

  metal atoms lose electrons to become positively charged

  non metal atoms gain electrons to become negatively charged
• electron transfer


  during the formation of an ionic compound can be represented by a dot and cross diagram

  
• ionic lattice


  diagram to represent:

  
• properties of ionic compounds


  strong electrostatic attraction

  high melting and boiling points

  when solid - ions are fixed in place

  when molten/dissolved ions can move and conduct electricity

  brittle
• metallic compounds - bonding and structure

  metals consist of giant structures of positive metal ions

  outer shell of metal atoms are delocalised so are free moving

  metallic bonds form due to electrostatic attraction between positively charged metal ions and negative delocalised electrons
• properties of metallic compounds

  layers of ions slide over each other so metals can be bent making them malleable and ductile

  delocalised electrons can move through the metal and carry charge so metals conduct electricity and heat

  metallic bonds are very strong

  very high melting and boiling points
• Covalent bonding


  when atoms share pairs of electrons they form covalent bonds. these bonds between atoms are strong
• covalent bonding


  some covalently bonded compounds consist of small molecules

  some have very large molecules such as polymers

  some have giant covalent structures (macromolecules)

  
• simple molecules


  usually gases or liquids that have low boiling and melting points

  weak intermolecular forces between molecules

  intermolecular forces increase with size of molecule

  dont conduct electricity
• giant covalent structures


  solids with very high melting points

  strong covalent bonds
• types of giant covalent structures

  diamond

  graphite
• diamond


  each carbon is joined to 4 other carbons covalently

  this is the maximum number of bonds carbon can make

  very hard

  very high melting points

  does not conduct electricity
• graphite


  bonded to 3 other carbons forming layers of hexagonal rings which have no covalent bonds between the layers

  can slide over each other but weak intermolecular forces

  soft and slippery

  one electron from each carbon atom is delocalised

  conducts electricity

  
• diamond


  each carbon is joined to 4 other carbons covalently

  this is the maximum number of bonds carbon can make

  very hard

  very high melting points

  does not conduct electricity

  
• graphene and fullerenes - graphene


  single layer of graphite

  has properties that make it useful in electronics and composites
• graphene and fullerenes - fullerenes

  carbon can also form fullerenes with different numbers of carbon atoms

  molecules of carbon atoms with hollow shapes

  based on hexagonal rings of carbon atoms

  may contain rings with five or seven carbon atoms

  buckminsterfullerene was first to be discovered which has spherical shape
• graphene and fullerenes - carbon nanotubes


  cylindrical fullerenes with very high length to diameter ratios

  properties make them useful for nanotechnology , electronics and materials
• graphene and fullerenes - examples of uses


  fullerenes can be used as lubricants to deliver drugs in the body and catalysts

  nanotubes can be used for reinforcing materials
• nanoparticles


  nano   10-9

  nanoparticles are 1-100 nanometers across

  contain a few hundred atoms

  as the side of the cube decreases by a factor of 10 the surface area to volume ratio increases by a factor of 10

  nanoparticles include fullerenes

  a nanoparticle has different properties to the 'bulk' chemical its made from because of their high surface area to volume ratio
• nanoparticle uses


  nano-silver:

  kills bacteria - deodorants, sock lining

  nano - titanium dioxide:

  cannot be seen so are used in sunblock to block harmful UV lights

  self cleaning windows as they break down dirt
• risks of nanoparticles


  nanoparticles are so small they could enter bloodstream

  risks of them aren't yet known

  more testing should be done

  relatively new so long term effects unknown

  could enter and potentially damage the environment
• smart materials


  smart materials are responsive to certain stimuli

  types:

  shape memory alloys and polymers

  thermochromic materials

  photochromic pigments

  polymer gels
• shape memory alloys and polymers


  return to their original shape when heated

  uses for polymers include: sports equipment , gum shields and medical stitches

  uses for alloys include: car bodies and plates for bone fractures
• thermochromic materials


  change colour when reached a certain temperature

  used in mugs and spoons which change colour when hot
• photochromic pigments

  these pigments change colour when exposed to light

  used in sunglasses that darken when in bright sun
• polymer gels


  hydrogels absorb up to 1000x their volume in water

  certain stimuli can cause water to be released

  used in nappies , fake snow and hair gel