Topic 2

• Solid to liquid 


  • when a solid is heated its particles gain more energy
  • this makes particles vibrate more which weakens the forces holding the solid together
  • at the solids melting point the particles have enough energy to break free from their positions
• Liquid to gas


  • when a liquid is heated the particles gain more energy
  • this makes the particles move faster, which weakens and breaks the bonds holding the liquid together
  • at the liquids boiling point, the particles have enough energy to break their bonds and the liquid becomes a gas
• Gas to liquid 


  • as a gas cools the particles no longer have enough energy to overcome the forces of attraction between them
  • bonds form between the particles
  • at the boiling point so many bonds have formed between the gas particles that the gas becomes a liquid
• Liquid to solid 


  • when a liquid cools the particles have less energy so move around less
  • theres not enough energy to overcome the attraction between the particles so more bonds form between them
  • at the melting point so many bonds have formed between the particles that they are held in place, the liquid becomes a solid
• name for liquids turning to a solid?

  freezing
• name for ssolids turning into a liquid ?

  melting
• name for liquids turning to a gas ?

  boiling (or evapourating)
• name for gases turning to a liquid ?

  Condensation
• what are polymers ?


  lots of small units (monomers) linked together to form a long molecule that has repeating sections
• monomers in a polymer are joined by strong covalent bonds
• the intermolecular forces between polymer molecules are larger than between most simple covalent molecules so more energy is needed to break them
• intermolecular forces in polymers are still weaker than ionic or colvalent bonds so they have (generally) lower boiling points than ionic or giant molecular compounds
• in giant covalent structures all atoms are bonded to each other by strong covalent bonds
• giant covalent structures have very high melting and boiling points as lots of energy is needed to break the covalent bonds between atoms
• giant covalent bonds do not contain charged particles so they dont conduct electricity (even when molten) except for a few exceptions e.g. graphite
• main examples of giant covalent structures:

  • diamond - each carbon atom forms 4 covalent bonds in a very rigid giant covalent structure
  • graphite - each carbon atom forms 3 covalent bonds to create layers of hexagons, each carbon atom also has 1 delocalised electron
  • silicon dioxide - each molecule is one giant structure of silica and oxygen
• metal oxides and metal hydroxides are bases
• ionic bonding :


  when a metal and a non metal react together, the metal atom loses electrons to form a positive ion and the non metal gains these electrons to form a negative ion

  these oppositely charged ions are strongly attracted to one another by electrostatic forces (this attraction is called an ionic bond )
• how are ionic bonds represented ?


  dot and cross diagrams
• what are ions ?


  charged particles (they can be single atoms or groups of atoms)
• when metals form ions they lose electrons in their outer shell to form positive ions
• when non metals form ions they gain electrons in their outer shell to form negative ions
• ionic compounds have a structure called a giant ionic lattice
• ions form a closely packed regular lattice arrangement and there are ery strong eletrostatic forces of attraction between oppositeley charged ions in all directions of the lattice
• ionic compounds all have similar properties:


  • high melting and boiling points due to the many strong bonds between the ions - it takes alot of energy to overcome this attraction
  • when they are solid the ions are held in place so they cant conduct electricity
  • when they are melted the ions are free to move and they can carry an electric charge
  • some ionic compounds also disolve in water - this seperates the ions and they are all free to move in the solution allowing them to carry electric charge
• when non metals bond together they share pairs of electrons to make covalent bonds
• the positivley charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces, making covalent bonds very strong
• molecules with triple covalent bonds contain three shared pairs of electrons
• molecules made up from only one type of atom are called monatomic molecules
• molecules made up from more than one type of atom are called polyatomic molecules
• a compound is formed when two or more elements chemically combine in fixed proportions to produce a substance with different properties from its constituents
• in covalent bonds atoms only share electrons in their outer shells
• coarse particles : have a diameter between 2500nm and 10000nm (also called dust)
• nanoparticles have a diameter between 1nm and 100nm, these are particles that contain only a few hundred atoms
• nanoparticles have a high surface area to volume ratio, this can cause the materials of a material to be different depending whether or its a nanoparticle or whether its in bulk, e.g. youll often need less of a material thats made up of nanoparticles to work as an effective catalyst compared to a material made up of 'normal' sized particles
• Diamond:


  • giant covalent structures
  • made up of carbon atoms that each have 4 covalent bonds
  • this makes diamond really hard
  • those strong covalent bonds take alot of energy to break
  • means it has a very high melting point
  • doesnt conduct electricity
• Graphite:


  • carbon atoms only form 3 covalent bonds, this creates sheets of carbon atoms arranged in hexagons
  • there are not any covalnt bonds holding these layers together - they are only held together weakly so thy are free to move over each other, this makes graphite soft and slippery (so its ideal as a lubricating material)
  • high melting point
  • each carbon has 1 delocalised electrons so graphite can conduct thermal energy and electricity
• graphene: 


  • one layer of graphite
  • it is just one atom thick making it a 2 dimensional substance
  • extremly strong and light
• metalic bonding:

  • the elctrons in the outer shell of metal atoms are delocalised (free to move around) there are strong forces of electrostatic attraction between the positive metal ions and the shared negative electrons
  • these forces of attraction hold the atoms together in a regular structure and are known as metalic bonding, metallic bondig is very strong
• solids :


  • strong forces of attraction between particles, which holds them close together in fixed positions to form very regular lattice arrangement
  • the particles dont move from their fixed positions so all solids keep a definite shape and volume
  • the particles virbrate about their positions - the hotter the solid becomes the more they vibrate