[Bioionic]

I have this question:
Q: A neutral atom has the following ionization energies given in KJ/mol;

1st IE 786
2nd IE 1580
3rd IE 3230
4th IE 4360

The element is most likely.

a. sodium
b. magnesium
c. aluminum
d. carbon
e. silicon

From looking at a chart in my book, I can see it is Si, but we will not have our books for the exam.  Do I need to remember the ionization energies for all the atoms?  That seems absurd, so I must be missing something. How would I figure out this question without my chart?

Thanks

[vhpk]

I have this question:
Q: A neutral atom has the following ionization energies given in KJ/mol;

1st IE 786
2nd IE 1580
3rd IE 3230
4th IE 4360

The element is most likely.

a. sodium
b. magnesium
c. aluminum
d. carbon
e. silicon

From looking at a chart in my book, I can see it is Si, but we will not have our books for the exam.  Do I need to remember the ionization energies for all the atoms?  That seems absurd, so I must be missing something. How would I figure out this question without my chart?

Thanks

I think the question needs to give you more figures in 5th and 6th or more IE to give a conclusion, but it's a MCQ question, so we see that 4th IE gets the maximum value -> atom has 4 electrons in the outer layer, but C has much greater IE than Si, and u see the first IE is relatively low, conclude that's Si.
Just my opinion. Hope to be contributed

[macman104]

You see that there is a large jump after the second ionization energy.  That indicates that after pulling off 2 electrons, you have a certain increased stability.

You can eliminate Sodium, Aluminum and Carbon because Sodium and Aluminum would display a large increase after 1 electron.  Can you see why Sodium and Aluminum would display an increased stability after only 1 electron loss.

The carbon, you can eliminate because it should not display a large jump in energy after 2 electrons have been removed.

Now you have Magnesium and Silicon left.  If you look, they both will display a certain stability after 2 electrons have been taken away.  However, after 2 more electrons the magnesium isn't at any certain "stability" area, but silicon will be at a noble gas configuration.

[Bioionic]

Cool, I think I get it. Thanks to you both.
Na has a 3s1 shell, so it would end up being stable with 2p6. Al has 3p1. So once they are stable it would take a lot of energy. Mg being 3s2 would be stable after losing 2 e-.  Ok I think I understand, but just what do we consider a lot of energy to say move Mg to 3rd level?

Thanks

[macman104]

Very good!  That is exactly why Na and Al don't match.

Actually, I misspoke.  We need to see the 5th ionization energy to distinguish between Mg and Si honestly.  If we see that the 5th energy is much higher than the 4th, then we can conclude that after 4 electrons lost, the resulting configuration is very stable (this would be Si).  If we saw that the 5th one was similar to the 4th one, then we could conclude that this was Mg (although, there might still be a larger increase due to it being 2p3, which is half-filled).

However, regardless of all that, you understand the process that you would use to distinguish between different elements.  If you understand the concept (which it seems you do), you should be ok.  If your professor gives you a question that requires the use of values without giving you them, then he's an ass .

Unless I'm missing a distinction between Mg and Si...

[Bioionic]

My bad.  There was a fifth value. 5th  IE 16100 KJ.  I rechecked.
Sorry, I am kinda tired. 

Thanks a bunch

[macman104]

My bad.  There was a fifth value. 5th  IE 16100 KJ.  I rechecked.
Sorry, I am kinda tired. 

Thanks a bunch

Hahahaha.  So yea, that's a huge jump, so what can you conclude from the resulting stability of the configuration of the element after it's lost 4 electrons?  Which element do you think it is?

[Bioionic]

Thank you very much.