atoms and ions query

State which neutral atom an O^5+ ion would most closely resemble and state its electron configuration. Then using this information, to explain how you would expect the ionisation energy of an O^5+ ion to compare with that of an O^6+ ion.

Is this at all possible?

 

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As you are new here, I will give you this one free, and close with some advice,* but do not like doing your home work, it that is what this is.

If you strip 5 electrons from typical O isotope you have still 8 protons in the nucleus and 8 neutrons with three electrons in orbit. It would most resemble lithium.

The inner shell would be filled by the two 1s electrons and the outer by the single 2s electron, which would be, to first approximation 8/3 times harder to remove. I.e. the ionization potential of lithium times 8/3; however we can do a little better than this by noting in both cases the the two 1s electrons mask the positive charge of the nucleus, but only partially. I.e. when lithium's 2s electron is pull away, something like only a net of 2, not 3, positive charges are resisting. (If I assume the two 1s electors are 50% effective in assisting the 2s electron to leave.)

Keeping this same 50% effective assist assumption, then the 2s electron of the O+5 ion is being removed from a net of 7 , not 8, positive charges. Thus, a alternative guess may be that the ionization potential of O+5 to O+6 ion is more like 7/2 times the IP of Li. At least one can be confident that it is more than 8/3 times Li's IP.

As the 1s electrons may be in classical terms in smaller diameter orbits about the 8 protons, and the 2s electron also there is greater distance for it to travel to get free than in the case of lithium to consider also. Even if O+5 is only slighly more compact than Li, the fact the potential well it must climb out of goes as the inverse of the separation from the nucleus is important too. Thus the IP of O+5 should be closer to the 7/2 than the 8/3 factor. This is also true because, again speaking classically, some of the time the 2s electron is inside the inner shell (It has to be as it has zero angular momentum.) so it is "feeling" the full force of the 8 protons holding it then.

Summary: To make a WAG, as I would be confident to guess about the IP of O+5 is not less than 3 times the IP of lithium.

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*Here is the promised advice:
Study harder, do your own homework as I did. – That is how I got the understanding to answer your question. After you have done this a while, you will find it is fun to learn as you can relate so many more things to each other. Furthermore, even when old as I am, you will still remember them. Memory is funny that way. It is easier to remember four related / inter acting / things than only one fact.

PS, If you are in highschool, your teacher may be expecting the 8/3 answer.
I.e. Too much knowledge is a dangerous thing also at times.

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