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Simple multiple choice questions on First ionization potential help please

Are the answers to 14 and 15 a and b respectively ?
854EDFB0-B9D5-4F5E-AAAA-D92A284FCF10.jpg
And shouldn’t the order in 23 be C O N F in increasing order ?
3ABC86C6-FF4A-42AB-A5A3-C609E35EDE67.jpg
(edited 4 years ago)
I think 14 is a
15 is e?
Xe and Sr are in the same period but ionisation energy increases across the period so Sr should be lower. Also ionisation energy decreases down the group and these are in the lowest numbered period so I think it is Sr
Original post by Leah.J
Are the answers to 14 and 15 a and b respectively ?
854EDFB0-B9D5-4F5E-AAAA-D92A284FCF10.jpg
And shouldn’t the order in 23 be C O N F in increasing order ?
3ABC86C6-FF4A-42AB-A5A3-C609E35EDE67.jpg

23. Is C
You are comparing second ionisation energies. i.e. X+ --> X2+ + 1e. These are endothermic values, energy is needed.

Fluorine has the highest nuclear charge and hence the greater attraction for the outer electrons. So you would expect F>O>N>C
BUT, you have to take into account which electron is being removed, and to do this you need the electronic configuration of the single positive ion.

F+: 1s2 2s2 2p4
O+: 1s2 2s2 2p3
N+: 1s2 2s2 2p2
C+: 1s2 2s2 2p1

You can see that fluorine has a pair of electrons in the px orbital, increasing the inter-electron repulsion and reducing the energy needed to remove the electron.

This places the oxygen in the first place and gives the order of decreasing ionization energies as: O>F>N>C

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