Can you help me with this Chemical Bonding problem?

Question

How do I figure out which noble has had the same electron configuration as each of the ions in the following compounds?

 

A. Cesium sulfide 

B. Strontium fluoride 

C. Calcium nitride 

D. Aluminum bromide

Answer 1

If it is an anion, look at the noble gas that immediately follows that ion. If it is a cation, look at the noble gas that immediately precedes that ion.  Example:  F^-, O^2-, Na⁺, Mg²⁺ all have the same electronic configuration as Ne (are isoelectronic with Ne).  

(A) Cesium sulfide = Cs₂S = 2Cs⁺ and S^2-.  So, Cs⁺ is isoelectronic with Xe and S^2- is isoelectronic with Ar.

(B) Strontium fluoride = SrF₂ = Sr²⁺ and 2F^-.  So, Sr²⁺ is isoelectronic with Kr and F^- is isoelectronic with Ne.

Got it?  You try the last 2.  If you can't get it, let me know.  You should have, in no particular order, the following noble gases as your answer.

Ne, Ar, Kr and Ne (not in the order they appear in the question).