DAT Chem Destroyer 2010 #233

[GoBlue24]

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I was wondering if anyone can confirm if Dr. Romano's explanation for #233 of the Chem Section of DAT Destroyer 2010 is wrong or not? I just want to make sure I'm not missing any key concepts if he is, indeed, right.

#233. Which of the following is false?

Answer is E: "The strontium cation (Sr+2) is larger than the sulfur anion (S-2) since negative ions gain electrons."

Dr. Romano's Explanation: Sr++ is smaller than S-- since it forms a positive ion. Choice E is clearly false.

Am I missing something? Sr++ still has an entire shell than S-- even after you take into account the addition/loss of electrons. I personally thought E was false because choice E's explanation does not make sense. Sr+2 is larger than sulfur anion due to an extra shell, NOT because S-2 gains electrons (in this specific case).

 

[R1Guy]

I was wondering if anyone can confirm if Dr. Romano's explanation for #233 of the Chem Section of DAT Destroyer 2010 is wrong or not? I just want to make sure I'm not missing any key concepts if he is, indeed, right.

#233. Which of the following is false?

Answer is E: "The strontium cation (Sr+2) is larger than the sulfur anion (S-2) since negative ions gain electrons."

Dr. Romano's Explanation: Sr++ is smaller than S-- since it forms a positive ion. Choice E is clearly false.

Am I missing something? Sr++ still has an entire shell than S-- even after you take into account the addition/loss of electrons. I personally thought E was false because choice E's explanation does not make sense. Sr+2 is larger than sulfur anion due to an extra shell, NOT because S-2 gains electrons (in this specific case).

I agree with you that this is a mistake. In the Sr+2 ion the 4th shell is completely full; and in the S-2 ion the third shell is completely full. So yea, Sr+2 is clearly larger than S-2.

Choice E was probably intended to say the CALCIUM ION is larger than the sulfur anion. Then the two would be isoelectronic ( and the DAT loves having you compare isoelectronic ions) and his explanation would make perfect sense. Just remember if they are isoelectronic (same number of electrons) whichever atom has MORE PROTONS will be smalller since it will have a stronger pull on the electrons, therefore contracting it, and making it smaller.

Good eye catching that!