Octet Exceptions

[sallina_yehdego 2E]

Why are H, He, Li, and Be exceptions to the octet rule?

[Shubham Rai 2C]

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 according to the periodic trends they are likely to lose electrons and become cations (Li+, Be2+). When that happens, they would have an electron configuration of a "noble gas" (He), which is only 2 electrons. So for these four elements, a full shell doesn't consist of 8 electrons, but 2 electrons.

[Abbey Brandt 1K]

He (Helium) has two electrons in its outer level. Look at its placement on the periodic table. Since there is no 1p subshell, 1s is followed immediately by 2s, and so level 1 can only have two VE at the most. H only needs one additional electron to be stable, and can accomplish this through covalent or ionic bonding. This leads to hydrogen having two electrons in its valence shell—the same electronic configuration as helium—when they form molecules by bonding to other elements.

[RoopshaChatterjee 1G]

If Li and Be are exceptions due to their metallic characteristics then why are other metals not exceptions as well?