E + O2 ---> O3
Ozone - O3 - Allotrope or Allotropic
2 forms of the same element that differ in their molecular or crystal structure & hence their properties
STRUCTURE OF THE ATOM
Nucleus - protons (+) ---> atomic #
Atomic Mass ---> Isotopes
Electrons (-) -> ion
1. responsible for periodicity of properties
2.levels or shells
a) d ÿ attraction
b) d ÿ energy
outer e- most important for accounting for similarity in chemical. props
"If you understand bonding you’ll understand chemistry" A.D. 1890
Single or covalent bond 2 shared e-
H:H Lewis structure named after Joe Bxsfts
Octet Rule - you want to fill the outer orbit with Eight (8) e- Þ the orbits hold Þ 2, 8, 8
What if you have 6 or 4 electrons?
.. .. .. ..
O:: O or O = O
.. .. .. ..
:N:::N: or :NºN:
3. harder to break
This is modeling Þ
O - O = O
O = O - O
All this is a General Rule to guide
you. Look @ p.41-44 Lewis Structures
Light - separate O.H.
The Oxygen/Ozone Screen
O2 + photon Æ 2O
UV Æ l < 242 nm (10-5 Æ10-6 cm) or 1 x 10 -9m
O3 + photon Æ O2 + O
UV Æ l < 320 nm
**Bonds are E specific!!!**
So O2 can screen the hi E UV ---> plants thrive
What about UV 242 - 320 nm?
Ozone more reactive than O2 what does this suggest about its bonding?
So what happens to UV reaching the Earth’s surface?
UV & You
To tan or not to tan? That is the question.
ÿ l F E DNA Damage
Geographic location is most important!!!
40 km S. latitude = 1% O3 ÿ
Every day 300,000,000 tons of O3 DESTROYED!!!!!!
Chapman Cycle pg 52 -53
Why are there arguments
1. Concentrations vary
2. intensity, of radiation varies
3. temperature change
4. react rate changes w/altitude
Ozone Distribution (Fig 2.7, p. 54)
NOTE - Log scale with error bars
Paths for O3 destruction
UV photon + H2O Æ H · + ·OH
Note Æ · is an unpaired electron
The ·H and ·OH (hydroxyl) are FREE RADICALS. (the · can go anyplace - H· )
Free radicals are unstable chemical
species with unpaired electrons. They are highly reactive.
The following is not in your text
H· + O3 Æ OH· + O2
OH· + O Æ H· + O2
We can combine this into one equation
H· + OH· + O3 + O Æ H· + OH· + O2 + O2
O3 + O Æ 2O2
Catalyst - chemical substance that participates in a reaction and influences its speed of reaction without undergoing a permanent change
Why It takes 6 hrs to London.
SST flies @ 15 - 20 km & ?
E + N2 + O2 Æ 2NO· (free rad)
Where Did All The Ozone Go?
320 DU in NH vs 250 DU in Quito - Why?
CFCs are chlorofluorocarbons
CFC -12 is Freon - 12 ->
CF2Cl2 or CCl2F2
The Lewis structure is very easy
Cl - C - Cl
Halogens - Family 7A
Fluorine is the most reactive element
Halogen compounds are very common, esp. Cl
CFCs however are very inert -> 120 yrs. at sea level
CCL2F2 + E (UV) Æ CClF2 +Cl·
l £ 220 nm
Cl· + O3 Æ ClO· + O2
ClO· + O Æ Cl· + O2 or
Cl· + ClO· + O3 + O Æ 2O2 +Cl· + ClO·
the Cl is catalyzing O3 destruction! ~100,000 O3 molecules before being carried into the lower atmosphere (<30km) to form HCl and ClONO2
Is man the only cause?
Natural (Fig 2.11, p.61)
But what about the Antarctic O3 Hole?
What to do?
1. Go back to iceboxes - yeah right!!!
How your ‘fridge works - (OH, Fig. 2.10, p.59))
1.toxicity ---> rem NH3 & SO2
3. extreme stability
how about? F
F -- C -- F
F This IR absorption!
1. Add an H? BOOM!!!
2. Add a Cl? UGHHHHH....
composition, molecular structure, BP
these all ÿ Eff E
The Big Mac and You