DAT Destroyer Ionization Energy Problem

[Locdawgg]

---

Members don't see this ad.

I found a topic on this already but it didnt specify why.

Question 67 DAT Destroyer 2013 Gen Chem

Element X has the first three ionization energies of 610, 1150, and 5200 KJ/mole. What is the most likely formula of a phosphate of X?

A. XPO4
B. X2PO4
C. X2(PO4)3
D. X3(PO4)2
E. X(PO4)3

The book states the answer is D because " Element X has a +2 charge since it is seent hat the first two ionization energies re low relative to the third ionization energy. Thus X2+ and PO4 -3 yields X3(PO4)2.

How does the first two ionization energies being low indicate that it has a +2 charge?

 

[ASOT]

Because the first 2 ionization energies are so low, those two electrons are easily removed. The 3rd ionization energy being so high indicates that it requires A LOT more energy to remove that electron- meaning this electron is probably the last in a sub-shell. So because the first two ionization energies are so low you know that is has a 2+ charge. I hope this helps!

 

[FeralisExtremum]

The 3rd ionization energy being so high indicates that it requires A LOT more energy to remove that electron- meaning this electron is probably the last in a sub-shell.

The 3rd ionization energy being so high would indicate that the energy required to remove that third electron is high because it is the first in a completely new shell down (not the last of sub-shell), but I think this is what you meant and your explanation otherwise is correct.

If it helps OP, here is an example in practice: if the element is Magnesium, we are going from Mg to Mg+ (1st ionization energy, removed electron from 3p2 ) --> Mg 2+ (2nd ionization energy, removed electron from 3p1) --> Mg 3+ (3rd ionization energy, removing electron from 2p6 - we are now pulling electrons from the 2nd shell rather than the 3rd - considerably closer to the nucleus, which is why there is such a big jump in ionization energy here).

 

[ASOT]

The 3rd ionization energy being so high would indicate that the energy required to remove that third electron is high because it is the first in a completely new shell down (not the last of sub-shell), but I think this is what you meant and your explanation otherwise is correct.

Haha yes, sorry about that. I like to just look at the periodic table and think about it which is why I used the word last.

 

[biomolecmed]

If the third ionization energy value is abnormally high, that means that from second to third value there is a huge increase. If so, that means the element is in the second column, therefore has 2+ charge. Answer D works.

 

[Daneosaurus]

Great ansewers, guys! Tonight is orgo (test tomorrow) and bio review. I forgot all about this aspect of gen chem.

On behalf of the OP, and myself, thank you!