Octet rule exceptions

[Yuehan_Wu_3K]

In the lecture, "E-transfer resuls in octet e- for each atom(exception H, He,Li,Be)" Why exceptions for those atoms?

[Jasmine Ho 3I]

For H and He, it's because those only have electrons in the 1s orbital (H has 1, He has 2), so they cannot have a full octet. Not really sure about the other 2 to be honest, but thanks for reminding me to look into that!

[Sarah Salam 1J]

Be has 2 valence electrons, and Li tends to lose an electron and go down to two instead of going up to 8, so they do not form an octet.

[505352202]

Sulfur is also part of this group of exceptions. It can hold 10 electrons, and that is why we refer to it as an expanded octet.

[Sunny Wu 3A]

For H and He, a valence shell with two electrons is stable, and thus they have no need to further react. For Be and B, resonance structures in which they do have an complete octet are very unstable due to the formal charges that would be in place.

An alternate explanation would be:
Hydrogen, beryllium, and boron have too few electrons to form an octet. Hydrogen has only one valence electron and only one place to form a bond with another atom. Beryllium has only two valence atoms, and can form only electron pair bonds in two locations. Boron has three valence electrons, and can form only electron pair bonds in three locations.

[Maddie Turk Disc 2J]

So this is why H can never be in the center of a molecule right? Since it can only hold 2 electrons?

[MCalcagnie_ 1D]

Going off of the idea that valence electrons are determined by the column number, why are only H, He, Li, and Be, the exceptions, and not the whole 1 and 2 columns?

[Catherine Bubser 2C]

Do these named exceptions depend on which elements these specific exceptions bond with, or are these rules across the board?

[Rylee Mangan 1K]

More exceptions to the octet rule are the elements Phosphorus, Sulfur, and Chlorine. These elements have an expanded octet and can hold more than 8 electrons (going up to 18).
Also, group 13 elements can hold less than 8 electrons, however they complete their octet if another atom provides both electrons to form a coordinate covalent bond.

[Mari Williams 1K]

Will we need to know these exceptions? Where would they come up in a test?

[Dominic Benna 2E]

Those are the exceptions because they will not get up to 8 valence electrons. They will either gain electrons to gain a full shell of two electrons or lose a certain number of electrons to have a full shell of two valence electrons.

[Gian Boco 2G]

These atoms do not have up to 8 protons and therefore do not have enough to fullfill 8 valence electrons in its outer shell.

[Jerry_T]

Be and Li tend to lose electrons so they don't form a full octet. H and He only have electron(s) in the 1s orbital (max of 2 e-) so they don't form a full octet.

[Cassidy Cheng 1J]

Will we need to know these exceptions? Where would they come up in a test?

I would definitely know these exceptions for the test. If we are asked to draw Lewis structures involving these elements, we would only get the correct answer if we know that H, He, Li, and Be don't have octets.

[Madeline Ogden 3B]

So this is why H can never be in the center of a molecule right? Since it can only hold 2 electrons?

Yes this is correct. A hydrogen atom can never be a central atom because it's only capable of forming 1 bond.

[Vanessa Perez]

Thank you everyone who answered this question. I was having trouble understanding this topic too