First four elements

[cecilia1F]

Hello,
I was wondering if anyone could clear up what Dr. Lavelle said during the lecture today- the first four elements will not form full octets. What does this mean in terms of their properties and what should we know about this in terms of making lewis dot structures?
Thank you!

[Noa Popko 3I]

I believe the first few elements do not form octects because if we were to hypothetically add so many electrons to fill the outer shell, there would be too much electon - electron repulsion in such a small area which is not favorable. In terms of Lewis structures, I think we should make sure that they don't make too many bonds in comparison with how many electrons they have.

[Kevin Zhang 3K]

The reason why the first four elements do not meet the octet rule is that their valence shell can only contain 2 electrons. If we check the electron configuration of the first four elements, we only get the s subshell. Elements past beryllium have the p subshell which increases the valence shell by six which makes the total eight.

[cecilia1F]

Hello,
This makes sense, thank you! I guess we could think of them as having their own "octet rule" in the sense that they fill their outer valence shell, but not with 8 electrons.

[Junyong Wu]

I think it is because they don't have 8 valence electrons after forming chemical bonds.

[Ella Bogomilsky 2B]

I think the first four elements don’t follow the octet guideline because the orbitals don’t allow for 8 electrons. For example, lithium only has 3 electrons that go up to the 2s orbital, so if it formed an anion there would be 2 electrons in the valence shell, not 8.

[Katie 3H]

How is electron-electron repulsion unfavorable?