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1. Density of water and ice

   • have ice- raise its temperature to 0 degrees celcious, ice melts and density increases
     • unusual
     • Ice has a very open structure- each water molecule is H-bonded to 4 others arranged tetrahedrally
     • As ice melts- the structure collapses, water molecules become closer together- density increases
       • Only a partial collapse of the structure- continues to 4 degrees C
         • water = max density
           • above this temp, have thermal expansion and so density drops again
             • explains why pipes burst if they freeze, and why icebergs float
               • Also ponds freeze from the top down- layer of ice insulates the water underneath, if ice sank there would be no insulation- more likely to freeze solid killing fish

2. Poly(ethenol)- a water soluble polymer

   • you would expect it to be made by addition polymerisation of ethenol ( but doesn't exist)
     • INSTEAD polymerise the monomer which has an ester group (COOH3) instead of OH group
       • After polymerisation- ester groups are hydrolysed to OH groups. IF ALL ester groups changed to OH- the polymer would be insoluble in water- H bonds are too strong between adjacent polymer chains = too strong
         • By leaving SOME ester groups, (bulky groups) reduce H bonding btw polymer chains- get a water soluble polymer. OH of polymer and water (h bonds)
           • However if too many ester groups are left, reduces number of h bonds that can form to water

3. Infrared Spectroscopy

   • useful technique at determining the structure of organic compounds
   • identify different types of covalent bonds, hence draw conclusions about functional groups in molecule

4. E/ Z isomerism

   • Stereoisomerism- isomers have identical formular and atoms bonded together in same way, but arrangement different
     • E- high priority groups on opposite sides
     • Z- high priority groups on the same side

5. Alcohols- OH functional group

   • Primary/ secondary/ tertiary alcohols
   • Oxidation of alcohols
     • Primary alcohol
       • aldehyde
         • Carboxylic acid
           • COOH
         • COH
       • Secondary alcohol
         • Ketone
           • C-O-C
         • Tertiary alcohol
           • Does not oxidise, remains orange
         • Dichromate turns from orange to green (reflux) slower than primary, less H's
       • Dichromate changes colour from orange to green, Distillation (to get aldehyde) Reflux (to get carboxylic acid)
   • Fehlings test- testing for carbonyls
     • fehlings in 2 tubes, add aldehyde/ ketone separately
       • water bath
         • aldehyde- turns fehlings solution from dark blue to brick red ppt
           • ketone remains unchanged- dark blue

6. Atmosphere

   • Radiation and matter
     • Each bond has its own natural frequency of vibration that depends on the type of atoms forming the bond and the type of bond (single/double/triple)
       • When molecule exposed to IR radiation, each bond absorbs energy at a particular frequency, causing it to vibrate more vigorously. Different bonds absorb different frequencies
         • Translation: molecules moving, gets faster, eg. side to side
         • Rotation: increasing energy of moving molecules. eg. spinning
         • Vibration: bond vibrates faster
         • Electronic changes:
           • absorption/emission- electronic excitation, electrons changing energy levels.
           • Homolytic fission- dissociation, the covalent bond undergoes homolytic fission to form radicals
           • ionisation- creation of a charged ion
     • E= hf
       • energy (1 photon J)= planck's constant (6.63 x 10 ^-34) X frequency (Hz)
     • C-F bond is stronger than C-Br bond, so it takes more energy to make C-F bonds vibrate. Therefore C-F absorbs infrared radiation of higher energy/ frequency than C- Br
     • When electrons in atoms absorb visible/ UV radiation the electrons mover to higher energy levels.
       • Molecules- eg chlorine molecule. the electrons occupy definite energy levels, both bonding and non bonding electrons. outer shell electrons are in highest energy level and can easily be moved to a higher energy level.
         • When molecule absorbs radiation:
           • electron can be excited to a higher energy level, later falling back to lower level (chlorine looks green- unabsorbed light)
           • if higher radiation used, molecule absorb so much energy that molecule breaks apart (dissociation - photodissociation) radicals form- very reactive
           • very high energy photons - so much energy provided that electron can leave- molecule can be ionised
   • parts per million
     • % --> ppm
       • x/100 x 1000000
     • ppm--> %
       • x/100000 x 100
   • Troposphere, stratosphere, mesophere, thermosphere
     • BTW stratosphere and mesophere is OZONE LAYER - exothermic reactions
     • Temperature inversion: hot--> cold --> hot (exothermic reactions in stratosphere cause warming effect)

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