Lewis Structure - Molecular forms

[SodiumChanel]

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Uh...this might be a easy one for everyone but I am clueless...

Top score exam #3 - Questions 47

Which of the following has an octet on the central atom?

a. ICl4+
b. SeF4
c. PBr4+
d. IF3
e. BrF4-

The answer is C. Thanks for those who answer the question! 👍

 

[roquer2]

Uh...this might be a easy one for everyone but I am clueless...

Top score exam #3 - Questions 47

Which of the following has an octet on the central atom?

a. ICl4+
b. SeF4
c. PBr4+
d. IF3
e. BrF4-

The answer is C. Thanks for those who answer the question! 👍

Phosphorus has 5 valence electrons. 1+ formal charge means it has only 4 valence electrons. Since 4 Bromines are bonded to it, the atoms will all share their electrons. Therefore, 4 e- from P + 1 e- PER Br (so 4 e- in all) = 8 shared e-. Thus, this gives P a full octet.

If you don't understand what I'm talking about, draw out the lewis structure. Hope this helped

 

[ChrisM07]

I am a little lost too. I drew out the Lewis structure as well like you suggested.

5 Valence for P + 28 total for Br = 33 e-

33 minus the 8 e- that are held in the P/Br bonds and we are left with 25 that need to go around the whole thing (seems like I have 1 left over as well).

Not sure where to go from here either. I see that you figured out the formal charge. I did that as well (not shown) and got 1+ as well. What next?

 

[roquer2]

I am a little lost too. I drew out the Lewis structure as well like you suggested.

5 Valence for P + 28 total for Br = 33 e-

33 minus the 8 e- that are held in the P/Br bonds and we are left with 25 that need to go around the whole thing (seems like I have 1 left over as well).

Not sure where to go from here either. I see that you figured out the formal charge. I did that as well (not shown) and got 1+ as well. What next?

Whenever drawing out your lewis dot structures, I HIGHLY suggest making your bonds into electrons as well. That way you can see the e- being shared.

Corresponding to your picture, if you convert all those line structured bonds to electrons (1 line = 2 e-), you will see 8 electrons floating around P. Thus, giving it a full octet.

 

[SodiumChanel]

Aren't atoms starting in 3rd period have a special exception to how many electrons/bonds they can withhold? Does that not play any contribution this question? Thanks roquer2! haha 🙂

 

[roquer2]

The group you are referring to is group 13, the Boron family. This group has the exception, yes. The only trend worth knowing for periods is that they gain electrons going right. Know the differences between your groups and periods!

And to answer your question, no this doesn't apply to this question. Phosphorus is in group 15 and has 5 valence electrons. But because of the + formal charge, it has 4 it can share. Therefore, you will assume the Lewis structure will have 8 electrons floating around it when 4 other atoms are bonded to it.

I think you're overthinking this question quite a bit, which is alright. As long as you know the mistakes you are doing. I'm overthinking some other easy concepts in gen chem as well, but correcting them quickly. Just practice drawing simple lewis structures (CH4, CO2, etc) and don't use lines as bonds! Hope this helps