The ozone story

• the atmosphere


  troposphere - ground level

  stratosphere - ozone

  nitrogen (78%) oxygen (21%) argon (0.93%) = percent

  CO2 (399) parts per million
• conversions


  percent = /100 per million = /1,000,000

  % --> ppm = x10,000

  ppm --> % = / 10,000
• electromagnetic radiation


  visible and ultra violet lights are the principle radiations that could reach the surface of the earth inferred lights is the principle radiation emitted from the surface of the earth.
• high energy UV


  break chemical bonds within molecules. this can break down DNA bonds and can lead to damaged genes and lead to skin cancer.
• ozone gas --> O3


  a natural sunscreen found at the top of the stratosphere it absorbs high-energy UV.

  tropospheric ozone is toxic to life as it causes:

  photochemical smog

  attacks lung tissue

  weakens the immune system
• c = λv


  Speed = frequency x wavelength

  c = 3.00x10^8
• E=hv


  Energy = Planck's constant x frequency

  h =h = 6.63x10^-3
• Worked example


  1) frequency --> energy (E=HV)

  2) joules --> kilojoules

  3) kilojoules --> KJmol^-1
• heterolytic bond fission


  when both bonding electrons move to sit on one atom.

  this is most likely when the bond is polar and this forms ions.
• homolytic bond fission


  one bonding electron moves to sit on one atom and the other electron to the other atom
• Radicals


  -contain an unpaired electron

  -are unstable and highly reactive and dangerous
• chain reactions


  1) initiation (usually photodissociation) (no radicals --> 2 radicals)

  2)propagation (2 radicals --> 2 radicals)

  3) termination (2 radicals --> no radicals)
• ozone


  is an allotrope of oxygen is present in tiny amounts - absorbs high energy UV.

  very reactive so must be regenerated
• ozone production


  O2 molecules could split in two by photodissociation.

  this requires UV as the bond enthalpy is +498KJmol-1

  this ozone reaction stops harmful UV radiation reaching the earths surface.
• ozone reactions


  O2 + hv --> 2O. = reaction 1

  O. + O2 --> O3 = reaction 2

  2O. --> O2 = reaction 3

  O. + O3 --> 2O2 = reaction 4

  O3 + hv --> O2 + O. = reaction 5
• steady state


  if the production and depleation reactions of ozone should come to equilibrium.

  the rate of removal will equal the rate of formation.
• Halogen radicals


  Cl Br I F

  the carbon halogen bond in haloalkene molecules absorbs UV radiation.

  CH3X + hv --> CH3 =X.

  this releases halogen radicals these then react with ozone in a catalytic cycle
• distribution of ozone


  X. + O3 --> XO. + O2

  XO. + O. --> X. + O2

  overall = O. + O3 --> 2O2
• factors tha affect rates

  temperature

  pressure

  intensity of radiation

  surface area

  catalysts

  pH/ concentration
• Maxwell-Boltzmann distribution

  
• heterogenous catalyst


  form an intermediate

  solid catalyst = silver and tungsten are not good catalysts / platinum and nickel are good catalysts
• Homogenus Catalyst


  all gas or all liquid per sulfate ions and iodide ions catalysed by Fe 2+ or Fe3+ ions
• CFCS +HCFCs


  chlorofluorohydrocarbons

  low toxicity

  low reactivity

  high boiling point

  high stability
• Nucleophile


  molecule or anion with a lone pair of electrons that can donate to a positivity charged atom

  Eg: OH- Br- H2O NH3 Cl-
• Substitution


  a atom or group within a molecule is replaced by another atom or group
• nucleophilic substitution reactions

  
• naming haloalkenes


  primary: the carbon atom carrying the halogen atom is bonded directly to one other carbon atom.

  secondary: the carbon atom carrying the halogen atom is bonded directly to two other carbon atom.

  tertiary: the carbon atom carrying the halogen atom is bonded directly to three other carbon atom.
• naming continued


  alphabetical order

  commas between numbers

  dashes between numbers and words

  di = two

  tri = three

  tetra = four
• electronegativity


  a measure of the ability of an atom in a molecule to attract electrons in a chemical bond to itself
• reason for


  1. atomic radius = smaller radius means stronger attraction

  2. core charge = higher core charge means stronger attraction (nuclear charge - core electrons)
• increase down the group

  intermolecular forces

  melting point

  boiling point
• instantaneous dipole induced dipole


  the electrons in a molecule are in constant motion, and at a particular instant they may not be evenly distributed.

  down this is larger electron cloud.

  instantaneous dipole becomes bigger so more energy is needed to break the larger forces of attraction.
• permeant dipole induced dipole


  a molecule may contain a permanent dipole if two atoms in a bond have substantially different electronegative (slightly stronger)
• permeant dipole permanent dipole


  these are relatively strong a such molecules are likely to be liquids or solids.

  as you go down the table the boiling point increases as the dipole gets bigger/ larger so there are stronger forces of attraction needed to overcome.
• hydrogen bonding


  either:

  molecule with a small hydrogen atom made patriarchally positive by being attached to a highly electronegative atom.

  or

  a highlight electronegative atom with a least one lone pair of electrons for the h atom to get very close to interact with.