Chemistry 2A

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  • Chemistry 2A
    • Isotopes
      • "Different atomic forms of the same element, which have the same number of protons but a different number of neutrons."
      • They have the same atomic number but different mass numbers.
    • Ionic Bonding
      • Atoms lose or gain electrons to form charged particles (ions).
      • Ionic compounds have giant ionic lattices.
      • There are very strong electrostatic forces of attraction between  oppositely charged ions, in all directions.
      • Ionic compounds have high melting and boiling points due to the strong attraction.
        • When they melt, the ions are free to move and can carry electric current.
          • They also dissolve easily in water. The ions separate, are then free to move and carry electric current.
      • It is between a metal and a non-metal.
        • Group 1 and 2 elements are metals, they lose electrons and form positive ions.
        • Group 6 and 7 elements are non-metals, they gain electrons and become negative ions.
    • Covalent Bonding
      • Atoms share electrons so that they've got full outer shells,
        • Having a full outer shell gives them the electronic structure of a noble gas.
      • Substances with covalent bonds can either be simple molecules or giant structures.
        • Simple Molecules.
          • The atoms form very strong covalent bonds to form small molecules.
          • The forces of attraction between the molecules are very weak.
            • Because of these weak intermolecular forces, the melting and boiling points are very low.
          • They don't conduct electricity because there are no ions so there is no electrical charge.
        • Giant Structures.
          • All of the atoms are bonded to each other by strong covalent bonds.
            • They have very high melting and boiling points.
          • They don't conduct electricity (except for graphite).
          • The main examples are diamond and graphite.
    • Metallic Structures
      • Metals consist of a giant structure.
      • Metallic bonds involve delocalised ('free') electrons.
        • This makes metals good conductors of heat and electricity.
        • They allow the layers of atoms to slide over each other, allowing metals to be bent and shaped.
      • There are strong forces of electrostatic attraction between the positive metal ions and the negative electrons.
      • Alloys
        • The atoms are different sizes which distorts the layers, making it harder for them to slide over each other.
          • Alloys are harder than pure metals.
    • New Materials
      • Smart materials behave differently depending on the conditions, e.g. temperature.
        • An example of a smart material is Nitinol. It is used for glasses frames and dental braces as it is a "shape memory alloy."
      • Nanoparticles are minute and contain a few hundred atoms.
        • Many new uses of nanoparticles are being developed.
          • They have a huge surface area to volume ratio so they could help make catalysts.
          • Nanotubes conduct electricity so can be used in tiny electric circuits.
    • Polymers
      • Forces between molecules determine the properties of the plastic.
        • Thermosoftening polymers have individual tangled chains of polymers which are held together by weak intermolecular forces. This means it's easy to melt so you can remould it.
        • Thermosetting polymers have stronger intermolecular forces between the polymer chains called crosslinks. These polymers are strong, hard and rigid.
      • Low density and high density polythene can be made using different conditions.
        • LD polythene = heat ethane to 200°C under high pressure. It's flexible so is used for bags and bottles.
        • HD polythene = made at a lower temperature and pressure with a catalyst. It's more rigid so is used for water tanks and drainpipes.
    • Chromatography
      • Paper Chromatography
        • Use pencil to draw the baseline.
        • Put the filter paper in a beaker with the solvent but keep the solvent below the baseline.
      • Gas Chromatography
        • The time the substances take to reach the detector is called the retention time.
        • The recorder shows a gas chromatograph - the number of peaks shows the number of different compounds.
        • It can be linked to a mass spectrometer which identifies substances leaving the column.
      • Advantages of using machines = very sensitive, very fast and very accurate.
  • Metals consist of a giant structure.

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