Mechanisms Chem Unit 2 Pt 7

Joining two or more molecules together to form a larger molecule. (eg. adding species across double-bond)

Splitting a molecule into two new molecules by adding H⁺ and OH^- derived from water. (Often requires a catalyst) (haloalkanes can be hydrolysed to form an alkali)

Reaction involving two or more monomer molecules with double bond, which breaks and the monomers join to form a polymer - a giant molecule.

When one species is replaced by another in a molecule.

Any reaction in which an atom loses electrons.

Any reaction in which an atom gains electrons.

• When a small group of atoms breaks away from a larger molecule without being replaced.
• Involves removing atoms from adjacent carbon atoms and the formation of a double bond between them.
• (eg. you can remove halogen and hydrogen from halogenoalkane to form alkene).

Any reaction where electrons are transferred between two species.

• Free radical substitution of chlorine in alkanes to make chloroalkanes
• elctrophilic addition of bromine and hydrogen bromide to alkenes, to make bromoalkanes.
• LOOK AT NOTES, REVISION BOOK, and HAND-MADE FLASHCARDS!

• A species that attacks an area of high electron density (eg. double bond). It will form a covalent bond with a pair of electrons from the electron-rich site. They are election pair acceptors.
• They can be positive ions (eg. H⁺) or slightly positive atoms (eg. H in HBr) or neutral molecule once polarised (eg. Br-Br)

• A species with a lone pair of electrons that is used to form a covalent bond. They attack a slightly positive atom on a molecule. They are election pair donors.
• Can be negative ions (eg. OH- or Cl-) or neutral species containing O or N (eg. water)

An atom or group of atoms with an unpaired electron that is used to form a covalent bond. Formed from homolytic bond fission, they are very reactive.

• Covalent bond breaks "unevenly". Both electrons from the shared electron pair move to one atom.
• Forms 2 species
• An electrophile (positively charged cation)
• A nucleophile (negatively charged anion)

• Cavalent bond breaking evenly. One electron from shared pair move to each atom.
• Forms - 2 electrically uncharged free radicals (atom with unpaired electron)
• Because of unpaired electron, free radicals are very reactive.

• O₂ absorbs UV radiation to form 2 oxygen free radicals. Oxygen free radicals then combine with O₂ molecules to form O₃.
• UV can also reverse formation of ozone by; O₃ + UV --- O₂ + Ofree-radical.
• An equilibrium is set up between oxygen molecules and oxygen free radicals, with ozone. This continuous making and destroying of ozone absorbs UV which is dangerous high energy radiation.

• Cl free radicals were formed when CFC's were broken down by UV light.
• This Cl free radical act as a catalyst and react with ozone to form a free radical ClO and O₂. This then reacted with more ozone to form O₂ and Cl free radicals.
• Overall reaction: 2O₃ ---- 3O₂ (where Cl free radicals are the catalyst - as it is regenerated, it can attack many ozone molecules)

• Unreactive, non-flammable, non-toxic. Used in fire extinguishers, propellants in aerosols, and coolant gas in fridges.
• But, in Montreal Protocol, international treaty was signed to phase out use of CFC's because they were destroying the ozone layer.

• Nitric oxide free radicals (NO-free radical) break down ozone into O₂. They react in the same way as chlorine radicals do. They act as catalysts.
• Come from nitrogen oxides, which are produced by aircraft engines etc.
• NO^o + O₃ --- O₂ + NO₂^o
• NO₂^o + O₃ --- 2O₂ + NO^o