Exceptions for Octets [ENDORSED]

[Ysabelle Magat 1E]

I understand that H, He, Li, and Be are exceptions to the octet rule, but can someone explain why exactly these four elements are exceptions? Thanks!

[Angela Harrington 2L]

I'm not sure about why Li and Be are exceptions to the octet rule, but H and He are exceptions because they are in the 1s shell and can therefore only hold a maximum of 2 electrons.

[Lawrence Tran 2H]

I was able to actually find this same question on Chem Community from 2015! viewtopic.php?t=6008

According to Rachel Lin:
"H and He are exceptions to the Octet Rule because for them, a full shell is only 2 electrons (the 1s shell). Li and Be are metals, and so they are likely to lose electrons and become cations (Li+, Be2+). When that happens, they also revert to the "noble gas" configuration of He, which is 2 electrons. So for these four elements, a full shell doesn't consist of 8 electrons, but 2 electrons."

That makes sense, its easier for Li and Be to lose 1 or 2 electrons to reach noble gas configuration rather than gaining 6 or 7 electrons.

[Caitlyn Lo 2F]

H and He are exceptions because their electron shell can only hold two valence electrons. Li and Be are also exceptions to the octet rule because they are more likely to lose an electron than gain 6 and 7 electrons to complete an octet.

[Andrew Nguyen 1E]

These four elements are exceptions to the octet rule due to their size. H and He have only 1-2 protons. It would take a lot of energy to add 6-7 electrons to those atoms, likely due to electron repulsion and the relatively low effective nuclear charge, so H and He only have a maximum of two electrons. For the same reason, Li and Be don't form octets. Both elements are relatively small and have less positive electron affinities (meaning energy is absorbed to add electrons). Additionally, the ionization energies for the two are comparatively low to following elements, meaning the elements would be more stable with 2 electrons, matching He-configuration.

[Helen Ringley 2E]

Li and Be would rather give away electrons because of their electron affinity, so they also will not form octets. H and He will not form octets because they only occupy the 1s orbital, which holds 2 electrons.

[Sophia Dominguez 3I]

H and He are exceptions to the octet rule because they are in the 1s subshell and can only hold a maximum of 2 electrons. Although Li and Be are in the 2s subshell, due to their electron affinity they are prone to lose electrons and become cations.

[Alejandra Hernandez 2A]

H and He are exceptions to the octet rule because they are both in the s group meaning that their electron shell can hold a maximum of two valance e-. The reason for Li and Bi also being part of these exceptions is because they are more likely to lose an election, than gain one and complete their octet. Hope this helped! :)

[BriannaDis2C]

H and He can only hold two valence electrons while Li and Be are also exceptions because they are more likely to lose one e- than gain 6/7 electrons to complete the octet rule.