What is the difference between a shell and an energy level? Why do shells have the octet rule but more than 8 electrons should be able to fit into any energy level above 2? My uni does a "structure and properties, electrons and quantum first" style of learning chemistry and im halfway through the semester and doing well on tests but i still dont understand this shit
>>7920914
Cool, how's Chem 101?
>>7920926
This guy thinks he's cool
>>7920914
>difference between a shell and an energy level
apparently none. In intro to chemistry, energy level is defined as the quantum number 'n,' and a shell relates to valence. If you ask a physicist however, they'll tell you that each energy level 'n' can hold n^2 pairs of electrons, making them basically the same thing.
I think the difference is just the perspective you view them from, which is taught for simplicity
[math]{\Psi _{n\ell m}}\left( {r,\theta ,\varphi } \right) = \sqrt {{{\left( {\frac{{2r}}{{na}}} \right)}^3}\frac{{\left( {n - \ell - 1} \right)!}}{{2n\left( {n + \ell } \right)!}}} {e^{ - r/na}}{\left( {\frac{{2r}}{{na}}} \right)^\ell }L_{n - \ell - 1}^{2\ell + 1}\left( {2r/na} \right)P_\ell ^m\left( {\cos \theta } \right){e^{im\varphi }}[/math]
>>7920937
so in the third shell there can be more than 8 but only up to 8 pop out and are valence?
thats mainly what im confused about
>>7920955
use dfrac for legible fractions
[math]{\Psi _{n\ell m}}\left( {r,\theta ,\varphi } \right) = \sqrt {{{\left( {\dfrac{{2r}}{{na}}} \right)}^3}\dfrac{{\left( {n - \ell - 1} \right)!}}{{2n\left( {n + \ell } \right)!}}} {e^{ - r/na}}{\left( {\dfrac{{2r}}{{na}}} \right)^\ell }L_{n - \ell - 1}^{2\ell + 1}\left( {2r/na} \right)P_\ell ^m\left( {\cos \theta } \right){e^{im\varphi }}[/math]
>>7920958
The octet rule is a mnemonic, nothing more.
n=1 has 2*1*1, or 2 electrons (helium, hydrogen)
n=2 has 2*2*2, or 8 electrons, hence the octet rule for those elements
n=3 has 2*3*3, or 18, which is a rule that becomes relevant when you study d-block/transition elements, but because of energy levels it's not quite as clear cut.
In case you ever wondered why sulfur could form 6 bonds, which clearly breaks the octet rule, this is why: look at what row sulfur is in.
>>7920969
damn i dont remember anyone ever telling me the octet is only for n=2. thats frustrating. what other lies and half-truths has academia forced on me
>>7920988
There are a lot, I'm graduating soon and I'm still hardly caught up. They're there for a reason though, a lot of the models can actually take you pretty far; there are some brilliant chemists out there who barely understand quantum mechanics.
What really fucks with me are these two;
1) s, p, d etc. orbitals don't actually exist, they're all degenerate in a vaccuum and the distinction is some sort of mathematical deconstruction illustrating angular momentum in an intuitive way (also the effects of crystal ligand fields)
2) a necessary requirement of the pauli exclusion principle is that all the electrons in a system are indistinguishable from one another
>>7920988
>what other lies and half-truths has academia forced on me
that spin a feature from the symmetry group in special relativity.
spin is not a quantum feature.
>>7920969
That is Bohr's atomic model, before we had the quantum mechanical model. In my country it is still taught before quantum model, because of its simplicity. Bohr's model is not wrong per se, just inaccurate and inadequate to explain all the phenomenons.
>>7920955
>>7920963
\displaystyle works also
[math]
\displaystyle
{\Psi _{n\ell m}}\left( {r,\theta ,\varphi } \right) = \sqrt {{{\left( {\frac{{2r}}{{na}}} \right)}^3}\frac{{\left( {n - \ell - 1} \right)!}}{{2n\left( {n + \ell } \right)!}}} {e^{ - r/na}}{\left( {\frac{{2r}}{{na}}} \right)^\ell }L_{n - \ell - 1}^{2\ell + 1}\left( {2r/na} \right)P_\ell ^m\left( {\cos \theta } \right){e^{im\varphi }}
[/math]
>>7921345
>just inaccurate and inadequate to explain all the phenomenons.
just like the quantum mechanical model.
>>7921411
Sure, everything is before everything is fully understood. Besides nobody yet understands quantum mechanics, it is work in progress.
