The two possible dot structures for ClF2+ ion are shown below. Which of the following is true?

Question

 

 

 

 

 

 

Which of the following is true?

 

Structure 1 is the correct configuration because fluorine prefers a formal charge of +1.
The formal charge on the Cl atom in structure 2 is −1.
The formal charge of both F in structure 2 is −1.

OR
Structure 2 is the correct configuration because the formal charge of F is zero and the formal charge of Cl is +1.

Answer 1

As you can tell from you answer options formal charge is important for this question so we will start there.  

Formal Charge = Valence electrons on atom - # of bonds - lone pair electrons

 

atom     F    F     Cl

VE        7    7     7

bonds    1    2    1

LPE       6     4    6

FC         0    1     0

 

and 

 

atom   F     Cl    F
VE       7     7    7
bonds   1     2    1
LPE      6     4     6
FC        0     1     0

 

OK, we can now eliminate the middle two answers because the central atom in both cases has a charge of +1 NOT -1. Now we look at electronegativity.  F is more electronegative than Cl which in this case means it will prefer a 0 charge to a +1 charge.  Therefore you answer is the last one.  

atom     F    F     Cl

VE        7    7     7

bonds    1    1    1

LPE       6     6    6

FC         0    0     0