H, He, Li, and Be Octet Rule

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Sebastian Hurtado 1J
Posts: 42
Joined: Fri Sep 25, 2015 3:00 am

H, He, Li, and Be Octet Rule

Postby Sebastian Hurtado 1J » Fri Oct 09, 2015 2:59 pm

Why are H, He, Li, and Be exceptions to the octet rule? What about the atoms of the element make them unable to reach a noble gas configuration?

Rachel Lin 2D
Posts: 20
Joined: Fri Sep 25, 2015 3:00 am

Re: H, He, Li, and Be Octet Rule

Postby Rachel Lin 2D » Fri Oct 09, 2015 3:05 pm

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.

Shaye Busse 3B
Posts: 20
Joined: Fri Sep 25, 2015 3:00 am

Re: H, He, Li, and Be Octet Rule

Postby Shaye Busse 3B » Fri Oct 09, 2015 4:56 pm

Additionally, the H atom does not necessarily need to fill its valence shell when forming ionic bonds. For example in an HF molecule, the H atom is the cation, meaning it has given up its single valence electron to bond with the F atom. By doing this, the H atom does not have a full valence shell, but rather has no valence shell to even fill while the F atom gains an electron to fill its valence shell.

Sebastian Hurtado 1J
Posts: 42
Joined: Fri Sep 25, 2015 3:00 am

Re: H, He, Li, and Be Octet Rule

Postby Sebastian Hurtado 1J » Mon Oct 12, 2015 4:12 pm

Thank you all for the clarification!


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