GC Destroyer 2013 #277

[swolly]

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Good morning guys, please take a look at the attachment for the question..

The answer in the back says that E is false, but this confused me. A-D are pretty clear. Ok so with E we're comparing a strontium cation and a sulfur anion.. Strontium loses 2 electrons and would have Kryptons configuration, while Sulfur would gain 2 electrons to get Argons configuration... So wouldn't the strontium ion still be larger than the sulfur anion? I know that in general if they have the SAME configuration that the anion is larger (e.g. if we were comparing sulfur anion vs Ca cation- both would have Ar configuration), but does the sulfur anion really get that much larger that its even larger than the Strontium cation in the next period? Please let me know what you guys think.. maybe this is a mistake in this version of the destroyer or maybe i'm just misinformed??

Sorry the pic is sideways btw...

 

[Danielqta]

Strontium loses 2 electrons, so it will have 38 protons and 36 electrons. Sulfur gains 2 electrons, so it will have 16 protons and 18 electrons. The configurations don't play a role in this. It's the amount of pull the nucleus has on the valence electrons. 38 protons will pull 36 electrons closer than 16 protons on 18 electrons. It's a cruddy comparison though. Why would you compare ions with a period gap inbetween.

 

[discensdentibus]

Yeah its a weird comparison. The cation of an isoelectronic species is smaller than an anion having the same amount of electrons. This case, you are battling two radii trends against one another, and in the end, even if it was Cs+ vs. F- (where F- is actually smaller), the rest of the sentence is just against all reasoning.

 

[swolly]

Appreciate it guys, Ill just stick with anions are are bigger but hopefully i don't get something like this on the actual test or i might cry lol. Thanks!!

 

[discensdentibus]

If it's any consolation, I am positive Chad attests that that kind of comparison is beyond the scope of the DAT. Literally no idea how he knows that, though.

 

[Dotoday]

Cations are smaller than anions, that's all. So, if Sr lost electrons, it is positive. It is small.

 

[clutchfans]

The cation loses e- so it wants to hold on to its remaning e- tighter, thus the smaller ionic radius. Anions have more e- thus it holds its e- loser thus bigger radius.