Have the noble gases got the highest 1st, 2nd and 3rd ionisation energies in a perio

Noble gasses will always have the highest first ionisation energy in their period, due to smallest atomic radius, no significant increase in shielding. However, group one metals will have the highest second ionisation energy (excluding hydrogen of course) in their period and group two metals will have the highest third ionisation energy in their period, due to the significant decrease in shielding between the s orbital and the p orbital.

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Thank you very much ! But i dont really understand why the group two metals have the highest third IE would the group 1 not have the highest? Thanks again Is it because if you remove 3 electrons from a group 1 element then you would end up with a pair of electrons in the p orbital thus they would repel making the 3rd electron easier to remove!

I understand what you are getting at, but not exactly. As the ionisation energy increases across a period (from left to right), due to the atomic radius decreasing, therefore the outer electrons are closer to the nucleus, therefore they are more difficult to remove. Therefore, as the third ionisation energy of group one metals effectively changes the electron configuration to one of a p5 outer electron, the third ionisation energy of group 2 metals effectively changes the configuration to a p6 outer electron, and therefore the p6 election is more difficult to remove than the p5 electron, and therefore group 2 metals have a higher third ionisation energy.

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Consider period three: Na->Ar. IE1 is the removal, in all cases of an e- from the 3rd shell. Ar, with the most p+ will pull hardest. Now consider IE2 - the removal of an e- from the 3rd shell, except for Na, which only has 2nd shell e- to remove, so even though it has far fewer p+ than Ar, finds it so much more difficult to lose an e- since shell number (and therefore shielding) is much more important than p+ number (at least in period three). IE3 means both (and only) Na and Mg have to lose shell two e-, but which finds it harder? Mg, since it has more p+. Sorry about this all being on one line, but my return key doesn't work