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please help-second ionisation energies

basically chem q:

explain why the 2nd ionisation energy of sodium is greater than the second ionisation energy of magnesium?

My answer-
na+ has full outer shell (noble gas E.c) stable, so doesnt want lose/gain electrons- difficult to ionize, whereas mg+ will readily lose another electron-to gain full outer shell, so more energy needed to ionize sodium

Checked on internet-
someone wrote this-

Once sodium loses one electron it satisfies the octet rule because it now has 8 electrons in it's outermost shell. So it is stable. More stable than if it lost another electron (which would result in it having only 7 in the outermost shell). So you require more energy to pull out that second electron.

Magnesium on the other hand, needs to lose 2 electrons to satisfy the octet rule. So pulling out the second electron will be easy (coz it would rather be in a state with 8 electrons in the outermost shell). Hence .. second ionisation energy (energy required to lose the second electron) is greater in sodium than in magnesium

But mark scheme?!:
doesnt give any marks for above^!!!

Question- are ions with noble gas configs stable? why wont mark scheme let this?

Reply 1

Mockery

It is simply that the second electron to be removed in the Na ion is in the 2p orbital where as for magnesium the second electron is in the 3s orbital.

Electrons closer to the nucleus are held more tightly, less electron shielding and a greater charge ratio with the nucleus.

Reply 2

Yep

Original post by Mockery

D: thanks! but how do i know im sposed to write that!!!

Reply 3

letsbehonest

In Na+, the outer electron is closer to the nucleus because it has one less shell, there is more nuclear attraction making it difficult to remove electron. Mg is easy to remove as there are more shells between outer electron and nucleus so there is more of the shielding effect, so the nuclear attraction is weaker so less energy needed

Revising my socks off for unit 1!

(edited 11 years ago)

Reply 4

Yep

Original post by letsbehonest

In Na+, the outer electron is closer to the nucleus because it has one less shell, there is more nuclear attraction making it difficult to remove electron. Mg is easy to remove as there are more shells between outer electron and nucleus so there is more of the shielding effect, so the nuclear attraction is weaker making it easy to remove electron.

Revising my socks off for unit 1!

thanks ! im revising for unit 1 too but im so dead cuz eevryone makes everything seem simple but when i do exam i get blank mind ):