Exceptions to Octet Rule

[005493723]

Hi, I sometimes have a hard time recognizing when molecules/atoms don't follow the octet rule and it seems like Lavelle loves to use those in problems and on exams. Could someone tell me a way that they recognize/remember these exceptions? Or maybe just common ones that are good to memorize?

[katrinahuwang_1L]

Some common exceptions to the octet rule include Be and B, which will both have less than a full octet. With the periodic table, you can see that Be will likely form 2 single bonds and B will likely form 3 single bonds. Period 3 elements and beyond can have an expanded octet: the most common ones being Cl, P, S, I, Se, Sb, etc. I think a good section to practice the exceptions to the octet rule is Section 2C in the textbook.

Hope this helps!

[Maggie Black 1C]

One thing that I did before the second midterm to help review this concept was actually rewatching the lectures where he goes over this idea. He does multiple practice problems and mentions several helpful hints that I missed the first time around. This strategy can be a little tedious, but if you have the time, it definitely helps!

[Sneha Anantharaman2D]

Hi! How I memorized them is basically just looking over the notes and the lectures to make sure that I knew all the ones that Professor Lavelle actually talks about in lecture. In general, however, B and Be do not follow the octet rule since B is stable with only 6 electrons and Be is stable with only 4. In addition, any element in Period 3 and above can have expanded octets because they have space within the 3d sublevels for extra electrons when bonding with other species. I would suggest just going over the notes and the professor's explanations for why certain atoms can have more than 8 electrons.

[Simone Byun 1F]

Two common exceptions to memorize are Be and B which are both stable with less than 8 electrons. Furthermore, any element in period 3 or later is able to have expanded octets, or more than 8 valence electrons. This is because of the empty d orbital shell.