Applying Pauli Exclusion Principle and Hund's Rule

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KTran 1I
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Joined: Fri Aug 30, 2019 12:15 am

Applying Pauli Exclusion Principle and Hund's Rule

Postby KTran 1I » Sun Oct 20, 2019 10:51 pm

I understand the definitions of the Pauli Exclusion Principle and Hund’s Rule, but can someone clarify how they are applied. Thank you!

Vuong_4G
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Joined: Sat Sep 14, 2019 12:17 am

Re: Applying Pauli Exclusion Principle and Hund's Rule

Postby Vuong_4G » Sun Oct 20, 2019 11:02 pm

Pauli exclusion states that no orbital can have more than 2 electrons. For example, if the 1s orbital was filled with 2 electrons then you cannot add another one to it, you would have to go to the next orbital, which is 2s. In addition to that, two electrons in the same orbital must have different spins (one up and one down).

For Hund's rule, it simply means that you fill up empty orbitals before you start pairing electrons in the same orbital. Let's say you get to sublevel 2p and you have 2 electrons left. You would add them to two different orbitals rather than putting them in one orbital. This reduces electron-electron repulsion, and electrons naturally configure themselves in the least energy configuration possible.

Ashley Wang 1B
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Joined: Wed Sep 11, 2019 12:16 am

Re: Applying Pauli Exclusion Principle and Hund's Rule

Postby Ashley Wang 1B » Sun Oct 20, 2019 11:05 pm

Hi!
I think for me their applications become most apparent when I think about how they relate to electron configuration. Someone (kindly) correct me if I'm wrong, but it seems that these principles are essentially the basis for how we know the electron configuration of each atom, and can also help you reason out why certain exceptions exist (eg. Cr, Cu) because of how the electrons will be paired/unpaired to obtain the lowest energy. Hope this helped! :)

Anna Heckler 3I
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Joined: Wed Sep 18, 2019 12:18 am

Re: Applying Pauli Exclusion Principle and Hund's Rule

Postby Anna Heckler 3I » Sun Oct 20, 2019 11:09 pm

Pauli Exclusion Principle and Hund's Principle both come into play when determining how to fill electron orbitals. We can use PEP to ensure that two electrons do not have the same spin within the same orbital. We use Hund's Principle to ensure that orbitals are filled from lowest energy level to highest.

gferg21
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Joined: Sat Aug 17, 2019 12:17 am

Re: Applying Pauli Exclusion Principle and Hund's Rule

Postby gferg21 » Sun Oct 20, 2019 11:11 pm

When writing electronic structure diagrams and assigning quantum numbers, it is useful to know that each sub-shell of the greater orbital can only hold two electrons, and the electrons must be "spinning" in opposite directions. For the ms quantum number you use -1/2 and +1/2 to indicate which direction the electron is spinning (down or up, respectively). Pauli Exclusion principle is helpful just to know that only two electrons can fit into a sub-shell, and it's not a super applicable principle but just know it.

Tracy Tolentino_1C
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Joined: Sat Sep 07, 2019 12:17 am

Re: Applying Pauli Exclusion Principle and Hund's Rule

Postby Tracy Tolentino_1C » Sun Oct 20, 2019 11:11 pm

So for Pauli's Exclusion Principle, it states no more than 2 electrons per orbital and that the two electrons must be spin paired.
In electron configuration, the quantum numbers (n,l,m(l),m(s)) matter as there are four main orbitals: s,p,d,f
n is the principle quantum number and determines the size and energy of the orbital
l is the angular quantum number and describes the shape of the orbital
m(l) is the magnetic quantum number and describes the different subshells or orientation the orbital can have.
m(s) is the direction of the spin
Pauli's exclusion principle applies as it basically says no two electrons can have the same quantum numbers.
Hund's Rule basically states that electrons in same subshell must occupy the orbitals singularly before doubling occupied.
For example, oxygen has the electron configuration: 1s2 2s2 2p4
for 2p, it can be separated to 2px, 2py, and 2pz subshells. Each subshell can only hold 2 electrons and each must be filled with one electron before adding the second one.


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