TBR Ionization Energy Question

[LuminousTruth]

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When comparing the second ionization energy of Mg and Na, doesn't the Na have greater second ionization energy due to a GREATER effective nuclear charge that comes from the smaller electronic shell?

My reasoning: I thought it takes more energy to remove the second electron from Na because the second electron is in a full octet, so Na is unwilling to let it go. And since Mg still has its second electron in its 3s2 orbital, it would take a lower energy to remove that electron and stabilize its empty shell, and thus its complete 2p6 octet.

TBR said Mg had the greater second ionization energy. Can someone explain why?

Also, on an unrelated note: I know that across a period, the acidity increases. But to understand the concept, can someone explain to me fundamentally why that is the case?

 

[epsilion11]

Na+ has a higher second ionization energy than Mg+.

 

[cortana431]

You're right for that reason. Na has 1 valence electron, so that is the only electron outside the inner shell while Mg has 2 valence electrons. Mg correctly has a greater first ionization energy because there is a greater attractive force from the nucleus on 2 electrons than for the 1 valence electron in Na. But Na has a much higher second ionization energy because the next electron to be removed is in the inner shell;much more difficult to remove than a valence electron. Mg still has another valence electron so its second ionization energy is still relatively low.

 

[487806]

When comparing the second ionization energy of Mg and Na, doesn’t the Na have greater second ionization energy due to a GREATER effective nuclear charge that comes from the smaller electronic shell?

My reasoning: I thought it takes more energy to remove the second electron from Na because the second electron is in a full octet, so Na is unwilling to let it go. And since Mg still has its second electron in its 3s2 orbital, it would take a lower energy to remove that electron and stabilize its empty shell, and thus its complete 2p6 octet.

TBR said Mg had the greater second ionization energy. Can someone explain why?

Also, on an unrelated note: I know that across a period, the acidity increases. But to understand the concept, can someone explain to me fundamentally why that is the case?

TBR's probably wrong at that sense. Second ionization energy means removing two electrons, but Mg2+ is a stable ion due to complete octet. Na2+ is unstable because the stable octet is destroyed.