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Lewis structures that obey the octet rule

Posted: Tue Dec 09, 2014 11:28 am
by Madison Davis 3F
Hi! When a problem tells you to "use only Lewis structures that obey the octet rule," what does this mean? And also, does this mean no double bonds?

Re: Lewis structures that obey the octet rule

Posted: Tue Dec 09, 2014 12:13 pm
by HelenMach 1J
I am going to assume that it means that the atom in the middle is only allowed 8 valence electrons (besides the few exceptions that do not have eight electrons naturally). So only four bonds, double bonds should be allowed as long as it obeys the eight valence/octet rule...

If someone can confirm....

Re: Lewis structures that obey the octet rule

Posted: Tue Dec 09, 2014 6:46 pm
by Karen Batugo 1L
This video explains the exceptions to the octet rule pretty clearly.
https://www.youtube.com/watch?v=AMJiGX1uTJE

Re: Lewis structures that obey the octet rule

Posted: Tue Dec 09, 2014 9:34 pm
by Shreyesi Srivastava 2D
I agree with Helen. Double bonds do not indicate expanded octets; they are often used in order to obey the octet rule. All lewis structures should obey the octet rule except for a few special cases.

These include:
1. Species with an odd number of electrons, otherwise known as free radicals. An example a free radical would be the lone electron on N in the compound NO. Here is a lewis structure for NO: http://i.ytimg.com/vi/NGo8aV3oMCk/maxresdefault.jpg
2. Elements such as boron that never satisfy the octet rule. An example would be BF3. Here: http://2012books.lardbucket.org/books/b ... 57bc84.jpg
As you can see, the central atom (B) only has 6 electrons around it, rather than 8 to fulfill its octet.
3. Elements that have expanded valence shells, such as phosphorous and sulfur. They can accept more than 8 atoms. An example of this would be PF5. http://i.ytimg.com/vi/aqDYtjhSdBE/maxresdefault.jpg

Other than these three situations, I do not see why you would not obey the octet rule. Again, double or triple bonds still allow you to obey the octet rule.

I hope I interpreted your question correctly!