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Post by Amber9 » Wed Jul 24, 2019 11:50 am

I thought the answer was 1300 kJ/mol (oxygen is in group 6). Can you explain how no spin pairing changes the IE value?

Thank you!
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Re: NS FL3 CP Q7

Post by NS_Tutor_Mathias » Wed Jul 24, 2019 3:29 pm

Right, so 1300 kj/mol is what it actually is, the energy it really does take to kick an electron off an oxygen atom. But the question is asking what it would be if reality were simpler.

All this is saying is that you want to realize that oxygen is the first element in row 2 to have a paired electron in any orbital of the p subshell. Nitrogen has one in each, and oxygen has 4 total electrons in the p subshell, one pair and two singlets (see here:https://d2jmvrsizmvf4x.cloudfront.net/0 ... xample.jpg). This configuration is less stable and therefore easier to ionize - you have evidence of that in just the graph in figure 1, seeing as it's ionization energy is far lower than you would expect.

The question in turn wants you to realize what the prediction SHOULD have been, if electrons behaved in a much more predictable way - in that case, the increase in ionization energy from group 5 to group 6 should have been roughly equivalent to the increase going from group 4 to group 5. This gives you a value of approximately 1700 kJ/mol.

You are not expected to know the background information here, but you are expected to spot a prediction (regular increase in ionization energy) and a deviation from it (irregular decrease!).
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