halogenalkanes Flashcards
(19 cards)
what are halogenalkanes
alkanes but with one or more of the
hydrogen atoms replaced by a
halogen.
why is the carbon–halogen bond in halogenoalkanes polar
all halogens are more electronegative than carbon
what are organohalogens
molecules that contain at least
one halogen atom joined to a carbon chain
what are organohalogens compounds used for
-pesticides
-different polymers
what is the ozone layer
-found at the edge of the stratosphere
-approximately 10-40km above the Earth’s surface
what is Ozone (O3)
a gas that forms part of the ozone layer
-Ozone absorbs harmful ultraviolet radiation (UV-B) from the sun.
-double covalent bond and dative bond between 3 oxygen molecules
what is causing increased UV-B
radiation to reach the Earth’s surface and what does this do
- depletion of ozone layer
-causes increased
genetic damage to living organisms and increased skin
cancer
what is the reversible reaction between oxygen and ozone catalysed by UV radiation
O2 + O–>O3
how does the reversible reaction between oxygen and the ozone occur
-UV radiation causes O2 molecules to break down into oxygen radicals by
homolytic fission of the covalent bond.
O2 🡪 2O
-oxygen molecules combine with
oxygen radicals to form ozone
O2 + O O3
What interferes with the equilibrium of the reversible reaction of the formation of ozone
Human activity and the production of CFC’s
what are CFCs
-Chlorofluorocarbons
-compounds
containing chlorine and fluorine atoms such as CF2Cl2 and CF3Cl.
explain the properties of CFCs
-The carbon-halogen bonds in CFCs make them very stable and resistant to
break down for many years in the troposphere
-UV radiation
will cause the carbon-halogen bonds to break by homolytic fission
-C-Cl bond breaks the most easily and so forms chlorine radicals in the stratosphere
what does chlorine radicals catalyse
the break down of ozone
what is photodissociation
a chemical reaction in which molecules of a chemical compound are broken down by absorption of radiation
what is the mechanism of chlorine radicals when catalysing the break down of ozone
initiation –>CF 2 Cl 2 UV Cl ∙ +CF 2 Cl
Propagation 1–> Cl ∙ +O 3 →ClO ∙ +O 2
Propagation 2–>ClO ∙ +O ∙ →Cl∙ +O 2
when did the use of CFCs get banned by the montreal protocol
1987
what are HCFCs
-Hydrofluorochlorocarbons
-They are
less stable than CFCs and so break down before reaching the stratosphere.
-still produce chlorine radicals when they break down
what are chemists trying to develop to overcome the issue of chlorine radicals
-hydroflurocarbons (HFCs).
-these break down in the atmosphere and don’t contain chlorine.
what catalyses the breakdown of ozone
-Nitrogen(II) oxide radicals
-chlorine radicals
