Comments
joshuatyberg t1_j99sg8m wrote
When atoms form chemical bonds, they share or exchange electrons to become stable. Atoms are most stable when they have a full outermost shell of electrons. The octet rule says that atoms tend to gain, lose, or share electrons to have 8 electrons in their outermost shell because that's a very stable configuration.
The octet rule is based on observations of how different elements behave and how their electrons are arranged. However, there are exceptions to this rule, and scientists are still studying why certain atoms can have more than 8 electrons in their outermost shell and still be stable.
ArcadeAndrew115 OP t1_j99ug9r wrote
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
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
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
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)
taphead739 t1_j99z59y wrote
The octet rule is a pretty old and simplified model for chemical bonding. It is only applicable for second- and third-row main-group elements in the first place and even there you‘ll find many exceptions (for example: borane clusters, pentacoordinate carbon atoms). Still, many small molecules and most organic compounds follow the rule, and since it is easier to learn than the modern, more accurate bonding concepts, it is still widely taught.
Current research on chemical bonding is done with either molecular-orbital theory or valence-bonding theory, which are both based on quantum mechanics and were introduced in the early 1930s. Both theories have no need for an octet rule, and they are much more complicated. Sometimes, researchers still study whether a molecule obeys or violates the octet rule, but since 1) the concept has become redundant, and 2) many exceptions have already been found, this is no longer an exciting field of research.
DavidRFZ t1_j99sbxn wrote
They did this research almost a hundred years ago. The s and p electronics are the most active chemically and there are 8 of those in each level. The electron configuration if the nearest noble gas is usually the most stable chemically.
This is especially true of the non-metallic elements in the top-right corner which are most often present in large organic molecules. C,N,O and the halogens. P and S are interesting exceptions! They can have 10 and 12 instead of just 8.
Paaaaap t1_j9a3q85 wrote
You see, we know how atoms work by solving very complicated quantum mechanics equations (in the past by hand!) And we could learn things like the orbital shape and other useful properties.
Now, solving everytime equations is hard and most of the time in chemistry there are a lot of shortcuts to make life easier. The octet rule is one of those, and if you look at the f and d block, or the haufbau filling rules you see that the octet is not so much set in stone!
Also, in the past by looking ad atom emission and absorption spectra we could find out quite accurately the energy of the levels, and it his way we can really see how electrons occupy atomic orbitals !
[deleted] t1_j9c8xc8 wrote
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Formal_Raise_6567 t1_j9c9j26 wrote
Atoms have a certain number of electrons in their outermost shell, and this number determines the type of chemical bonds they can form. We know that atoms can't have more than 8 maximum outermost electrons because of the octet rule. This rule states that atoms will always try to fill their outermost shell with 8 electrons in order to achieve a stable electron configuration. This is why atoms prefer to form chemical bonds with other atoms that will give them 8 electrons in their outermost shell. Research is being done to understand why atoms prefer the octet rule. Scientists are studying the electronic structure of atoms and molecules to understand why the octet rule is so important for chemical bonding.
MercurianAspirations t1_j99t9lg wrote
Well we know for sure from experimentation that some molecules don't obey the octet rule, and a whole class of elements, the transition metals, obey an 18-electron rule rather than the octet rule. But the general principle that certain electron orbital configurations are more stable and lower-energy states, and therefore atoms will readily undergo reactions to achieve those states, generally holds true. The least reactive elements on the periodic table (the noble gases) already obey the octet rule, and the most reactive elements are those that only need a little energy (being only a few electrons away from a noble gas configuration in either direction) to get to such a configuration.