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H, He, Li, Be Rule

Posted: Thu Nov 01, 2018 9:21 pm
by Henry Krasner 1C
Is there any specific reason that the first four elements on the periodic table DON'T need an octet?

Re: H, He, Li, Be Rule

Posted: Thu Nov 01, 2018 9:23 pm
by Annalyn Diaz 1J
I would think that the first four elements on the periodic table don't need an octet because they would rather lose electrons than gain them. It would be very difficult and unstable if they were to somehow try to get an octet.

Re: H, He, Li, Be Rule

Posted: Thu Nov 01, 2018 9:53 pm
by timschaeffer Dis 1J
Another way to think about it is that to have 8 valence electrons for an octet you need to have at least an s-orbital (2 electrons) and a p-orbital(6 electrons) in the outermost energy shell.

The first 4 elements fill up as far as the 1s and 2s orbitals but never reach any p-orbital at all. Trying to get to an octet for these elements would mean having to establish a p-orbital AND fill it up. This would take way more energy than just staying with completely full s-orbitals.

Re: H, He, Li, Be Rule

Posted: Thu Nov 01, 2018 10:21 pm
by Jasmine Reddy DIS 1E
As others have said, hydrogen, helium, lithium, and beryllium only have s subshells. Each s subshell can only hold 2 e-. These elements do not have the p subshells required to hold 8 valence e-.