Lewis Structures

Question

Molecule AB2 forms with A as the central atom and a total of 18 valence electrons to share. (below are the answers I tried)

a.Draw the Lewis structure for Ab2

I drew A with a double bond to B and single bond to other B. Then, I drew the valence electrons to fill the octets accordingly.

b.Does the Lewis structure show resonance?

No

c.An AB single bond has a bond length of 150 picometers and an AB double bond has a bond length of 120 picometers. When the bond lengths in a molecule of AB2 are measured, neither bond length (120 or 150 picometers) is detected. Give a possible value for the actual measured bond length in AB2, and explain your answer.

?? I'm confused here.

Answer 1

Unfortunately, the Lewis structure cannot be drawn here, at least, not by me.  Your description of how you drew it is correct EXCEPT you didn't mention if you included a lone pair on the central atom A.  I assume you did, if you competed the octet.  

 

(b). Yes, the Lewis structure DOES show resonance.  You can have B=A-B or B-A=B.

 

(c) The actual structure is an average/combination of the two resonance structures, thus the bond lengths will not be "pure" single or double, but a combination/average.  So, one might expect the bond lengths to be approximately 135 picometers.