What is the Lewis Structure for NCS(minus) and how did you determine it?

Question

Please, what is the Lewis Structure for NCS-... I can't figure it out. Thanks for the help!

Answer 1

There are two possibilities. Follow this link for a picture of the first possibility. http://img175.imageshack.us/img175/8223/ncssh2.jpg

Basically, all 3 of these elements follow the octet rule (they want 8 electrons in their outermost shell), and as you can see, they all have 8. Now, S is carrying the - sign because it's formal charge is -1. Formal charge is calculated by Formal Charge=# of electrons the element has (S brings in 6) - the # of electrons it "owns" within the bond. Sulfur "owns" 7 in this case (3 lone pairs and one in a shared covalent bond--thus (3*2)+1=7.

Therefore Formal Charge of Sulfur (in this case): is -1 because

6-7=-1

I probably made it sound more confusing than it is. Sorry about that.

But other than that, you know that Carbon should be the central atom here because it's coming in with only 4 electrons in it's valence shell, so it's more needy than Nitrogen with it's 5 and Sulfur with it's 6. So you stick it in the middle and then pretty much trial and error.

The other possibility is here.
http://img175.imageshack.us/img175/6659/ncs2wf4.jpg

This time Nitrogen is carrying the -1 formal charge, because it comes into the bond with 5 electrons in it's valence shell, but it "owns" 6 in this case (2 lone pairs and 2 electrons out of the 4 in the N=C double bond..(2*2)+2=6. So...Formal charge of -1 comes from

-1=5-6

Even though these two molecules look different, they are in fact the same. This is a concept called resonance.

I hope this wasn't too confusing.

Answer 2

Ncs Lewis Structure

Answer 3

This Site Might Help You.

RE:
What is the Lewis Structure for NCS(minus) and how did you determine it?
Please, what is the Lewis Structure for NCS-... I can't figure it out. Thanks for the help!

Answer 4

Your structure is totally wrong. The middle nitrogen breaks the octet rule in that configuration.