The Ozone Story

What The Ozone Story covers

The storyline that carries intermolecular forces, kinetics and the haloalkanes: electronegativity and polarity, the Boltzmann distribution and catalysis, nucleophilic substitution, radical chain reactions, and the destruction of stratospheric ozone.

The 21 subtopics

Each one has its own page.

• Electronegativity and bond polarityRecall questions on the definition and trends of electronegativity, Pauling values, and when a bond and a molecule are polar.Open →
• Intermolecular bondsRecall questions on instantaneous dipole-induced dipole bonds, permanent dipole bonds and hydrogen bonding, and their relative strengths.Open →
• Boiling points and intermolecular bondsRecall questions on what is broken when a molecular substance boils, the halogen boiling point trend, and why ammonia boils above phosphine.Open →
• Activation enthalpy and enthalpy profilesRecall questions on the definition, symbol and units of activation enthalpy, why most collisions fail, and reading a profile.Open →
• Collision theory and the Boltzmann distributionRecall questions on the two conditions for a successful collision, what the Boltzmann curve shows, and how heating changes it.Open →
• Following a reaction and finding the rate from a graphRecall questions on ways of following a reaction, why a thermostatted bath is used, and finding a rate from the gradient of a curve.Open →
• Catalysts and alternative reaction routesRecall questions on how a catalyst lowers the activation enthalpy, why the reactant and product levels are unchanged, and why ΔH is unaffected.Open →
• Homogeneous catalysis and intermediatesRecall questions on what makes catalysis homogeneous, what an intermediate is, and the two steps of the chlorine radical cycle.Open →
• Composition of gas mixtures by volumeRecall questions on parts per million by volume, converting between ppm and a percentage, and applying it to atmospheric gases.Open →
• Recognising and naming haloalkanesRecall questions on the general formula and the halogen prefixes, naming a haloalkane, and the order in which prefixes are written.Open →
• Primary, secondary and tertiary haloalkanes, and the aminesRecall questions on classifying a haloalkane and an amine, and why the two classification rules are not the same.Open →
• Properties and nucleophilic substitution of haloalkanesRecall questions on why ethanol is added as a solvent, the boiling point trend, and the equations for hydrolysis by hydroxide, water and ammonia.Open →
• Substitution, nucleophiles and the SN2 mechanismRecall questions on what a nucleophile is, the curly arrows of the mechanism, and which bond breaks and which forms.Open →
• Relative reactivity of the haloalkanesRecall questions on the carbon-halogen bond enthalpies, the silver nitrate rate experiment, and why bond strength rather than polarity decides the rate.Open →
• Homolytic and heterolytic fission, radicals and half curly arrowsRecall questions on the two kinds of fission and what each produces, how a radical is written, and what a half curly arrow shows.Open →
• Initiation, propagation and termination in a radical chain reactionRecall questions on the three stages, why ultraviolet light is needed, and why the reaction gives a mixture of products.Open →
• Ozone depletion by haloalkanesRecall questions on what a CFC is, its photodissociation, the two-step catalytic cycle, and why an HCFC was an improvement.Open →
• Ozone in the stratosphere and troposphereRecall questions on where ozone sits, the equations that form and destroy it naturally, the steady state, and ozone at ground level.Open →
• Radiation of the Earth and the SunRecall questions on how the radiation the Earth receives differs from what it emits, and which regions of the spectrum do what.Open →
• Effects of UV and visible radiation on moleculesRecall questions on what absorption does to a molecule, why ultraviolet causes chemical change when infrared does not, and why one photon must carry the energy.Open →
• Calculations with frequency, wavelength and energyRecall questions on the relationships linking speed, frequency, wavelength and photon energy, and converting a photon energy to kJ mol⁻¹.Open →

What you need to know

Answer each one before you reveal it.

Take The Ozone Story further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Homolytic fission vs Heterolytic fission

  Homolytic fission: a bond breaking so that each atom takes one of the shared electrons. Heterolytic fission: a bond breaking so that one atom takes both of the shared electrons.

• Nucleophile vs Electrophile

  Nucleophile: an electron-pair donor attracted to an electron-deficient atom. Electrophile: an electron-pair acceptor attracted to a region of high electron density.

• Permanent dipole-dipole bond vs Instantaneous dipole-induced dipole bond

  Permanent dipole-dipole bond: attraction between molecules that have a permanent separation of charge. Instantaneous dipole-induced dipole bond: attraction from momentary uneven electron distribution inducing a dipole in a neighbour.

Questions from this topic

Each one with the model answer underneath.

1. 1

   Define electronegativity.

   Model answer

   Electronegativity is the ability of an atom to attract towards itself the pair of electrons it shares in a covalent bond.

2. 2

   How does electronegativity change from left to right across a period, and why?

   Model answer

   It increases, because the nuclear charge rises while the bonding electrons stay in the same shell with similar shielding, so they are pulled in more strongly.

3. 3

   How does electronegativity change down a group, and why?

   Model answer

   It decreases, because the bonding pair is held further from the nucleus and is screened by more inner shells.

4. 4

   Name the most electronegative element.

   Model answer

   Fluorine is the most electronegative element.

5. 5

   Using the values C 2.5, Cl 3.0, O 3.5 and F 4.0, place these atoms in order of increasing electronegativity.

   Model answer

   The order is carbon, then chlorine, then oxygen, then fluorine.

6. 6

   What makes a covalent bond polar?

   Model answer

   The two bonded atoms have different electronegativities, so the shared pair is pulled nearer the more electronegative atom, which becomes δ− while the other becomes δ+.

What is inside Levo

Six ways to work the same material.

The Ozone Story revision questions

What does The Ozone Story cover in OCR A-Level Chemistry B?

21 subtopics: electronegativity and bond polarity, intermolecular bonds, boiling points and intermolecular bonds, activation enthalpy and enthalpy profiles, collision theory and the boltzmann distribution, following a reaction and finding the rate from a graph, catalysts and alternative reaction routes, homogeneous catalysis and intermediates, composition of gas mixtures by volume, recognising and naming haloalkanes, primary, secondary and tertiary haloalkanes, and the amines, properties and nucleophilic substitution of haloalkanes, substitution, nucleophiles and the sn2 mechanism, relative reactivity of the haloalkanes, homolytic and heterolytic fission, radicals and half curly arrows, initiation, propagation and termination in a radical chain reaction, ozone depletion by haloalkanes, ozone in the stratosphere and troposphere, radiation of the earth and the sun, effects of uv and visible radiation on molecules and calculations with frequency, wavelength and energy. Each one has its own page with questions and model answers.

How is The Ozone Story organised?

By the OCR H433 specification, subtopic by subtopic, so it matches the order you are taught it in.