OZ Flashcards
typical composition of troposphere
78% nitrogen gas
21% oxygen gas
1% argon gas
small amounts of methane, carbon dioxide, neon and helium
mixing of gases vertically in troposphere and stratosphere
easy in troposphere - hot gases can rise and cold gases can fall
hard in stratosphere - reverse temperature gradient
PPM =
% composition x 10000
UV
most damaging part of electromagnetic spectrum to humans
absorbed by ozone in the stratosphere
UV B and UV C most damaging forms
high energy UV breaks down the molecules by breaking bonds and producing highly reactive radicals
vibrational energy
supplied by IR radiation
rotational energy
supplied by microwave radiation
electronic energy
corresponds to energy provided by visible light and UV
when an electron absorbs radiation:
electrons may be excited to higher energy levels
with higher energy photodissociation forming radicals may occur
with very high energy ionisation (removal of an electron) may occur
homolytic fission
one of the two shared electrons goes to each atom (fission producing radicals)
heterolytic fission
both of the shared electrons go to one of the bonding atoms, forming ions
atom which gains both the bonding electrons becomes negative ion
radicals
molecules or atoms with at least one unpaired electron, very reactive
initiation
initial reaction in which a molecule produces radicals by photodissociation
propagation
radicals react with another molecule and a new radical form
termination
two radicals react and no radical is produced
factors affecting rate of reaction
conc of solution/pressure of gas
surface area
intensity of radiation
temperature
explaining the effect of concentration/pressure on rate
higher number of particles per volume
increased frequency of collisions
particles collide with sufficient energy
hence increases rate
activation enthalpy Ea
minimum kinetic energy required by a pair of colliding particles before reaction will occur
transition state
highest point on the pathway of a reaction where old bonds stretch and break, and new bonds begin to form
breakdown of ozone by chlorine radicals
Cl + O3»_space; ClO + O2
ClO + O»_space; Cl + O2
overall : O + O3»_space; 2(O2)
importance of haloalkanes
used in fire retardants and as intermediates in medicine synthesis
attraction of shared electrons in molecules
shared electrons are attracted more strongly by the core of the smaller atom, which is closer
shared electrons are attracted more strongly by the atom with the greater core charge
electronegativity
measure of the tendency of an atom to attract a bonding pair of electrons
increases across a period and decreases down a group (increases towards fluorine)
polar covalent bonds vs non-polar covalent bonds
polar occurs where there is a significant difference in electronegativity of the atoms involved
non-polar occurs with equal sharing of the bonding electrons or when there is only a small difference in electronegativity (diatomic molecules)
trends in strength of intermolecular bonds (imbs)
bigger atoms/molecules have higher BPs because they form stronger imbs
longer chains have higher BPs because there are more points of contact for imbs
highly branched molecules have lower BPs because there are less points of contact for imbs
dipole
molecule with a partially positive end and a partially negative end because of its polar bond
permanent dipole
when two atoms have substantially different electronegativities
induced dipole
occurs when an unpolarised molecule is next to a dipole (dipole attracts/repels electrons in the unpolarised molecule, inducing a dipole in it)
instantaneous dipole
temporary dipole which arises when the electrons, which are constantly moving, in a molecule are unevenly distributed
all molecules have instantaneous dipoles
bigger molecules have more electons so produce more
types of imbs from weakest to strongest
instantaneous dipole - induced dipole (in all molecules)
induced dipole - permanent dipole
permanent dipole - permanent dipole
symmetrical molecules and dipoles
can have multiple bonds but no permanent dipole
negative charge is evenly spread across the molecule
requirements for hydrogen bonds
large dipole between a H atom and a highly electronegative ion (O, N or F)
small H atom which can get very close to the electronegative atoms in nearby molecules
a lone pair on the electronegative atoms that the +ve H atoms can line up with
MP and BP of fluorine
lower than the other halogens
has the weakest id-id bonds because it has the fewest electrons
BP of hydrogen fluoride
appears to have unusually high BP compared to the other hydrogen halides
has the ability to form H bonds and the others do not
more energy required to break H bonds than id-id bonds
nucleophile
molecule or -ve ion with a lone pair of electrons that it can donate to a +ve atom in order to form a covalent bond
nucleophilic substitution of hydroxide ion and haloalkane
heat under reflux with NaOH and ethanol
OH- attacks the carbon atom in the C-X bond
OH- donates pair of electrons to form a new dative covalent bond
C-X bond breaks heterolytically, producing X- ion
nucleophilic substitution of water and haloalkane
heat ender reflux (with water)
water molecule attacks carbon in C-X bond
lone pair on oxygen donated to form new dative covalent bond
C-X bond breaks heterolytically, producing X- ion
resulting molecules loses H+ to form an alcohol
nucleophilic substitution of ammonia and haloalkane
heat in a sealed tube (with ammonia)
ammonia molecule attacks carbon in C-X bond
lone pair on nitrogen donated to form new dative covalent bond
C-X bond breaks heterolytically, producing X- ion
resulting molecules loses H+ to form an amine
producing haloalkane from alcohol
halide ions are nucleophiles
requires presence of strong acid
