Ozone depletion chemistry
Hi
Is it only chlorine radicals that catalyst the destruction of ozone, or will other halogen radicals also do the same?
Also, what is the process by which the o3 form o2? How does the Cl. react with o3 to form ClO. Leaving o2? How does the o3 bond break in other words?
Thanks
Is it only chlorine radicals that catalyst the destruction of ozone, or will other halogen radicals also do the same?
Also, what is the process by which the o3 form o2? How does the Cl. react with o3 to form ClO. Leaving o2? How does the o3 bond break in other words?
Thanks
Hello.
Firstly, Cl. are not the only radicals that break down Ozone to form O2, there are other radicals such as hydroxy radicals, formed from the dissociation of water.
I think it would be good for you to understand some of the background, rather than just learning the facts..
Br radicals are actually 100 times more effective at breaking down the ozone, however they are much less abundant in the stratosphere- this is because C-Cl has a much shorter bond length than C-Br, if you can recall, because Chlorine's nucleus has a much higher charge density, and so the attraction to the covalent bond between the C-Cl is stronger and so will require more energy to break than C-Br, where the bromine has a lower charge density, and so the C-Br bond is weaker and will require less energy to break, because of this, the C-Br will be able to break lower down in the atmosphere where the UV is less intense, where C-Cl struggles to break as well- leading to more abundance of C-Cl in the stratosphere, and hence, why it is more of an issue.
The chlorine radical essentially has 1 free electron (unpaired) which is very reactive, as it wants to fill its outer shell. This chlorine radical will eventually collide with an O3 radical and will 'share' an oxygen from the O3, but it can only do this by bonding to it and hence a ClO forms. it does this because the relative reactivity of the chlorine radical is greater than the relative stability of the O3 molecule.
Thus the products are O2 and ClO, you may be thinking how do i know which one becomes the radical, well O2 is definitely not a radical, because each O has 8 electrons in their outershell, and so the Oxygen that the chlorine bonded too, broke a bond and only formed 1 bond with it because the chlorine only needs 1 electron to fill its outershell, so oxygen now has 7 electrons in its outershell, but oxygen needs 2 extra electrons as it's in group 6- meaning the oxygen must have 1 unpaired electron, and hence ClO is a radical.
ClO radical will then react with an oxygen radical that is floating around, due to the photodissociation of O2 in the atmosphere, but this time O2 is formed, leaving the Cl radical (the catalyst) unchanged at the end of the process. But, you need to try and see that the ClO radical will not always react with an O radical, because there are many different molecules in the stratosphere.
Firstly, Cl. are not the only radicals that break down Ozone to form O2, there are other radicals such as hydroxy radicals, formed from the dissociation of water.
I think it would be good for you to understand some of the background, rather than just learning the facts..
Br radicals are actually 100 times more effective at breaking down the ozone, however they are much less abundant in the stratosphere- this is because C-Cl has a much shorter bond length than C-Br, if you can recall, because Chlorine's nucleus has a much higher charge density, and so the attraction to the covalent bond between the C-Cl is stronger and so will require more energy to break than C-Br, where the bromine has a lower charge density, and so the C-Br bond is weaker and will require less energy to break, because of this, the C-Br will be able to break lower down in the atmosphere where the UV is less intense, where C-Cl struggles to break as well- leading to more abundance of C-Cl in the stratosphere, and hence, why it is more of an issue.
The chlorine radical essentially has 1 free electron (unpaired) which is very reactive, as it wants to fill its outer shell. This chlorine radical will eventually collide with an O3 radical and will 'share' an oxygen from the O3, but it can only do this by bonding to it and hence a ClO forms. it does this because the relative reactivity of the chlorine radical is greater than the relative stability of the O3 molecule.
Thus the products are O2 and ClO, you may be thinking how do i know which one becomes the radical, well O2 is definitely not a radical, because each O has 8 electrons in their outershell, and so the Oxygen that the chlorine bonded too, broke a bond and only formed 1 bond with it because the chlorine only needs 1 electron to fill its outershell, so oxygen now has 7 electrons in its outershell, but oxygen needs 2 extra electrons as it's in group 6- meaning the oxygen must have 1 unpaired electron, and hence ClO is a radical.
ClO radical will then react with an oxygen radical that is floating around, due to the photodissociation of O2 in the atmosphere, but this time O2 is formed, leaving the Cl radical (the catalyst) unchanged at the end of the process. But, you need to try and see that the ClO radical will not always react with an O radical, because there are many different molecules in the stratosphere.
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