Topic 2

• What are the three types of strong chemical bonds?


  ionic, covalent, metallic
• What is ionic bonding?


  transfer of electrons between non metals and metals
• what is covalent bonding?


  sharing of electrons between non-metals and non-metals
• what is metallic bonding?


  the chemical bonding between metal and metal that results from the attraction between metal atoms and the surrounding sea of electrons
• What is empirical formula?


  An empirical formula is the simplest ratio of whole number atoms of each element in a compound.
• what are polymers?


  long chains of very large covalent molecules
• Metallic bonding


  the atoms in metals are built up layer upon layer in a regular pattern.

  the electrons in the outer shell of metal atoms are delocalised and are free to move throughout the structure.

  the sharing of delocalised electrons leads to strong metallic bonds.

  they conduct heat and electricty
• what are limitations of dot and cross diagrams?


  Don't tell us about the shape of the molecule
• solid to liqud

  liqud to solid

  melting

  freezing
• liqud to gas

  gas to liqud

  evaportation

  condensing
• gas to solid

  solid to gas

  sublimation

  decomposition
• What does this symbol mean? (aq)


  aqueous (dissolved in water)
• Structure of an ionic compound


  Giant ionic lattice
• properties of an ionic compound


  high mp and bp

  can conduct electricity when molten or dissolved in water- ions are free to move and can carry charge
• Properties of small molecules


  low mp and bp

  most are gases or liquds

  do not conduct electricity, particles do not have an overall electrical charge

  larger molecules gave higher bp and mp as intermoelcular forces increase with the size of the molecules
• Properties of giant covalent structures


  very high melting and boiling points

  don't conduct electricity- not even when molten, paeticles dont have an overall electrical charge
• properties alloys


  harder then pure metals

  made from two or more different metals.
• why are alloys hard


  the different sized atoms of the metals distort the layers in the structure, making it difficult to slide over each other, so alloys are harder then pure metals
• properties of diamond


  each carbon atom forms four covalent bonds with other carbon atoms.

  very hard

  high mp and bp

  cannot conduct electricity as there are no free electrons.
• properties of graphite


  carbon atoms form 3 covalent bonds with three other carbon atoms.

  they form hexagonal ring layers

  soft and slippery- layers can easily slide as the forces of attraction are weak.

  used as a lubricant

  conducts electricity, electron from each carbon atom is delocalised.
• properties of graphene


  single layer of graphite

  conductor of thermal energy and electricity

  low density, string, used in electronics
• why are alloys harder then metals


  the different sized atoms of the metals distort the layers in the structure, making it difficult to slide over eachother, so alloys are harder then pure metals
• why are metals good conductors

  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
• examples of giant covalent structures


  diamond, graphite and silicon dioxide (silica)
• why can graphite conduct electricity?


  one electron from each carbon atom is delocalised
• what are fullerenes?

  Fullerenes are molecules of carbon atoms with hollow shapes. The structure of fullerenes is based on hexagonal rings of carbon atoms
• name a fullerene

  buckminsterfullterne (C60)
• What are carbon nanotubes?


  Carbon nanotubes are cylindrical fullerenes with very high length to diameter ratios.
• One use of fullerenes


  Drug delivery for cancer
• Use of carbon nanotubes


  reinforce materials
• what is nanoscience


  the study of particles between 1-100nm in size
• what is a nanoparticle


  A particle between 1 and 100nm in size
• Use of nanoparticles


  1) Catalysts

  2) Deliver drugs right to cells

  3) Some conduct electricity= used in electric circuits for computer chips

  4) Silver nanoparticles= antibacterial properties. Can be added to polymer fibres that are used to make surgical masks, wound dressings etc.

  5) Deodorant

  6) Cosmetics e.g. make moisturisers w/o making them too oily

  7) Sun cream
• problems with use of nanoparticles


  can cause damage to cells
• nanoparticles have a large..


  surface area to volume ratio
• what happens to the surface area as a particle decreases in size


  the surface area increases
• Properties of nanoparticles


  high surface area to volume ratio

  very flammable

  cheap

  conduct electricity

  antibacterial properties

  lubricants
• whats a polymer


  each polymer molecule is made up of smaller units- chain of monomers
• properties of polymers


  low mp and bp then ionic or covalent bonds but higher then simple molecular substance

  solid a room temperature