ArcadeAndrew115 OP t1_j99ug9r wrote on February 20, 2023 at 10:22 AM

Reply to comment by joshuatyberg in ELI5: How do we know for certain that atoms can't have more than 8 maximum outermost electrons when atoms form chemical bonds? Is there any research being done to see why atoms prefer the octet rule? by ArcadeAndrew115

I guess my further question which is more philosophical in nature, would then lead toward "why is 8 somehow the magic number that (mostly) all atomic particles follow for their stable bonds?"

like you and others have said though, some elements can have more than 8 and be stable which answers my question in a more broad sense because I learned thanks to yall (and googling it after reading these) that not all elements follow that rule! most do, but not all, and I wrote the question under the impression there were no exceptions to the rule!

Fascinating!

audioen t1_j9abd2n wrote on February 20, 2023 at 1:39 PM

I think the short and boring answer is 8 electrons can arrange into 4 electron pairs, which gives you tetrahedral symmetry with the atom in the center and its bonds extending towards the corners of the tetrahedron. As an example, CH4 has this structure. For many atoms, 4 outer electron pairs seems to be optimal in sense that atoms still can get close enough to share electrons without bumping to each other, and the pairs can still arrange into structures called orbitals where they can get as far as away from each other as possible in a deliberate way that is described by quantum mechanics.

When atom is floating alone in space, the orbitals are all distinct and create these quantum-mechanically allowed non-overlapping structures such as s, p and d orbitals, and so forth. When other atoms enter the picture, the situation changes and the orbitals are said to hybridize, which is to say that they are no longer like that but tend to combine and the picture is now more complicated. As an example, tetrahedral symmetry is result of 2 distinct orbital shell types combining together to yield this new structure of 4 identical covalent bonds.

First group elements tend to only create one covalent bond as their outermost shell is single spherical structure that can only fit 2 electrons, and they already have one themselves. Most other elements seem to prefer 8 electrons, likely because of the sweet spot of maximizing electromagnetic attraction with electrons and protons, while also still minimizing the electromagnetic repulsion between the electrons. Then there are transitional metals which are larger in diameter and create more complicated covalent bond structures, apparently between 12 to 18 electrons, and there electrons also make use of the d orbitals which tend to be more pointy and narrow in their shape, which is a general trend with all the higher orbitals.

ellipsis31 t1_j99vxte wrote on February 20, 2023 at 10:43 AM

There are always exceptions. For every rule there is some weird circumstance or extreme condition that breaks it. Our rules are constructed out of convenience because they fit basic circumstances and help us to learn.

When teaching chemistry we tend to teach a bunch of rules and then later teach the exceptions, because it's easier to understand the exceptions after you have the necessary base of knowledge.

beardyramen t1_j9a0z3r wrote on February 20, 2023 at 11:50 AM

Consider that in nuclear physics there are "magic numbers". I can remember 2, 4 and 8 being some of them, but at the moment i can't remember the rest.

These numbers are linked to very stable layouts, against unstable ones.

(Tritium is much less stable than deuterium for example) I don't think we have a definitive explanation as of how and why they work, but rember (as a very basic intuitive approach) that an even number of things can be easily arranged in symmetrical ways, and some arrangements are much easier to obtain than others (for example there are 8 evenly distributed vertices in a cube)