Page 1 of 1

Exceptions to Octet Rule

Posted: Sun Nov 11, 2018 5:24 pm
by 305115396
What are some exceptions to the octet rule that I should know for sure? Also is it true that basically all elements past period 3 don't obey the octet rule?

Re: Exceptions to Octet Rule

Posted: Sun Nov 11, 2018 5:28 pm
by Sarah Fatkin 4I
Hi! All elements above period 3 can have an expanded octet.

Re: Exceptions to Octet Rule

Posted: Sun Nov 11, 2018 5:28 pm
by Andrea Zheng 1H
Elements in period 3 have an empty d-orbital, so it does not have to obey the octet rule. Hydrogen, helium, beryllium, and lithium are exceptions to the octet rule because they form duplets. Radicals are also exceptions to said rule.

Re: Exceptions to Octet Rule

Posted: Sun Nov 11, 2018 5:39 pm
by anthony_trieu2L
Although elements in period 3 and beyond have an expanded octet (due to their ability to access their d orbital), it does not necessarily mean that they don't obey the octet rule. It is always best to assign each element an octet when drawing Lewis structures and to determine the best and most stable structure from there (based on the formal charges).

Re: Exceptions to Octet Rule

Posted: Sun Nov 11, 2018 5:51 pm
by Kevin Tang 4L
Andrea Zheng 3B wrote:Elements in period 3 have an empty d-orbital, so it does not have to obey the octet rule. Hydrogen, helium, beryllium, and lithium are exceptions to the octet rule because they form duplets. Radicals are also exceptions to said rule.


If radicals are exception to this rule, can they have nine valence electrons on their outer shell when they are not allowed to have an expanded octet (Nitrogen, Oxygen, Florine). Or do you mean by exception, that they can have seven valence electrons. If they have seven valence electrons, they have not exceeded the eight electrons on its outer shell.

Re: Exceptions to Octet Rule

Posted: Sun Nov 11, 2018 8:28 pm
by Keshav Bhatnagar 1H
You should know that elements in the first and second periods can have expanded valence shells due to the empty d-orbital. You should also know that Cu and Cr have electron configuration exceptions.