The Ozone Story
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what is homolytic fission?
one electron goes to each atom, forms radicals
what is heterolytic fission?
both electrons are transferred to one atom, forms a cation and an anion
what is a substitution reaction?
when a functional group in a compound is replaced by another functional group
what is a nucleophile?
an electron pair donor
what reagents and conditions are required for nucleophilic substitution of a haloalkane?
-warm aqueous NaOH heated under reflux
what reagents and conditions are required for nucleophilic substitution of haloalkanes with ammonia?
-warm a haloalkane with xs of ethanolic ammonia
what determines reactivity of a haloalkane?
-bond strength (decreases down group)
what happens in an initiation reaction?
• photodissociation causes bond to split homolytically - 2 uncharged radicals produced
How is Ozone made from Oxygen?
• O2 molecule absorbs UV, causing it to split into O radicals • radicals combine with O2 to give O3
what is a radical?
-a molecule with one unpaired electron
How is ozone made in the troposphere?
-effect of sunlight on mixtures of Nitrogen Dioxide and hydrocarbons
what are sources of atmospheric hydrocarbons and NO2?
• vehicle engines - power stations
what is photochemical smog and why is it dangerous?
• ozone mixed with solid particles of carbon and other substances • causes respiratory problems
what are CFCs?
haloalkanes that have all their hydrogen atoms replaced by chlorine and fluorine
where does the breakdown of CFCs occur?
in the stratosphere
how does the breakdown of CFCs result in destruction of the ozone layer?
• CFCs broken down by high energy UV, produce radicals • Cl radicals are catalysts + react w/ Ozone to make ClO and O • overall reaction is 2O3 -> 3O2
what is the percentage of Nitrogen and Oxygen in the Atmosphere?
N2 =78% O2 =21%
define ‘dipole’
a difference in charge between the two atoms caused by a shift in electron density
what is electronegativity?
the ability of an atom to attract the bonding electrons in a covalent bond
why might a molecule containing multiple polar bonds have no overall dipole?
polar bonds are pointed in opposite directions, they cancel out
explain how instantaneous dipole-induced dipole bonds arise?
• electrons in charge clouds constantly moving, this means that a temporary dipole can arise • this dipole can induce another, temporary dipole in another molecule
why do heavier molecules form stronger intermolecular bonds?
-larger molecules have larger electron clouds
why do longer chained alkanes have higher boiling points than more branched isomers?
-more molecular surface contact means that there are more electrons that can interact
why is ice less dense than water?
• in ice, the molecules are arranged so that there is the maximum amount of Hydrogen bonds, this ‘wastes’ space • when the ice melts, bonds can form closer together