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(once again this question is not a duplicate of any other question to my knowledge, and this should actually help alot of people trying to ionize air)
for one you can easily figure out that nitrogen is 15.58eV and oxygen is 13.6eV, but the problem is in the air nitrogen bonds with another nitrogen (N2) and oxygen bonds with another oxygen (O2). My chemistry teacher said that the 2 atoms eV dont just add up he said it shouldnt be to much more then 15.58eV. What does it add up to and what is the equation of figuring that out. I suprisingly cant find this anywhere on the internet, so an equation of some sort would help a bunch. thanks!

Qmechanic
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Reese Houseknecht
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  • What do you mean "nitrogen is 15.58 eV"? What property of nitrogen is 15 eV? – By Symmetry Nov 01 '17 at 13:30
  • So are you asking how to get ionized nitrogen atoms, or ionized nitrogen molecules, or what? This question is unclear. – Jon Custer Nov 01 '17 at 13:30
  • yes im looking to ionize these molecules, i know i could ionize nitrogen because i know its electronvolts, and 1240/15.58 = ~80nm. im looking to find the ev required to ionize the molecule thats all. and possibly the equation to help with that. – Reese Houseknecht Nov 01 '17 at 13:35
  • "I can't find this anywhere" - did you try looking in any molecular physics textbooks? This is elementary material (though there simply isn't a single equation to give you the molecular ionization potential) and it is covered in a slew of introductory books. – Emilio Pisanty Nov 03 '17 at 12:42

1 Answers1

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There isn't a simple way to get the ionisation energy of the molecule from the ionisation energies of the atoms that make it up. You have to either do a calculation of the molecular wavefunction or of course measure it experimentally.

When commenting on one of your previous questions I gave you the experimentally measured ionisation energies for $N_2$ and $O_2$ from the NIST web site. The ionisation energy of $N_2$ molecule is $15.58$eV as described here, and the ionisation energy of the $O_2$ molecule is $12.07$eV as described here. This compares to $14.54$eV and $13.62$eV for the nitrogen and oxygen atoms respectively.

John Rennie
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  • Oh my god! Thank you, so 15.58 is n2 and 14.54 is just plain nitrogen, your the best – Reese Houseknecht Nov 01 '17 at 16:55
  • Its funny how for all this time i thiught nitrogen was 15.58 and didnt even know that that was the air nitrogen – Reese Houseknecht Nov 01 '17 at 17:03
  • Just a quick question even though im mainly only worried about nitrogen, why is oxygen higher when its not bonded but when its bonded its lower? – Reese Houseknecht Nov 01 '17 at 17:04
  • @ReeseHouseknecht: There isn't a simple answer to that, but note that the trend continues as we move along the periodic table. The ionisation energy of $F_2$ is $15.7$eV and the ionisation energy of the fluorine atom is $17.4$eV. – John Rennie Nov 01 '17 at 17:11
  • Definitely weird but its new to me and im glad i know a little more then i did before! Thank you again – Reese Houseknecht Nov 01 '17 at 17:19