Quantum Numbers

[MedPR]

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Confused about n.

"There are n squared orbitals per shell"

???

 

[mcloaf]

Where are you getting that from? I believe that comes out of Schrodinger's wave equation, about which you need to know nothing for the MCAT...

 

[MedPR]

Where are you getting that from? I believe that comes out of Schrodinger's wave equation, about which you need to know nothing for the MCAT...

mcat-review dot org

Orbital structure of hydrogen atom, principal quantum number n, number of electrons per orbital

• In the Bohr model, the hydrogen electron orbits the nucleus.
• In quantum mechanics, hydrogen electron exists in a spherical probability cloud around the nucleus.
• The principle quantum number, n, defines what shell the electron is in.
• n values start from one: 1,2,3 ...etc.
• Higher n shells are higher in energy (if subshells are the same).
• There are n squared orbitals per shell.
• There are 2 electrons per orbital.
• Thus, there are 2n^2 electrons per shell.

 

[mcloaf]

Oh, actually, now that I see that written out that makes sense. It's just a trick to remember how many orbitals are in each shells. So for example in the second shell there are 2^2=4 orbitals, one 2s and three 2p orbitals. I have no idea why they'd bother to emphasize that as it's not hard to keep track of orbitals per shell anyway, especially with a periodic table to look at.

 

[Misfit138]

That's the rule for determining how many orbitals there are in a given shell. For example, for principle quantum number 3 (i.e. n=3), there are 3^2 = 9 orbitals. Stated slightly differently, there are 9 orbitals in the third shell of electrons. (one s orbital, three p orbitals, and five d orbitals)

 

[MedPR]

Oh, actually, now that I see that written out that makes sense. It's just a trick to remember how many orbitals are in each shells. So for example in the second shell there are 2^2=4 orbitals, one 2s and three 2p orbitals. I have no idea why they'd bother to emphasize that as it's not hard to keep track of orbitals per shell anyway, especially with a periodic table to look at.

That's the rule for determining how many orbitals there are in a given shell. For example, for principle quantum number 3 (i.e. n=3), there are 3^2 = 9 orbitals. Stated slightly differently, there are 9 orbitals in the third shell of electrons. (one s orbital, three p orbitals, and five d orbitals)

Oh! Thank you both.

 

[SaintJude]

Oh, actually, now that I see that written out that makes sense. It's just a trick to remember how many orbitals are in each shells. So for example in the second shell there are 2^2=4 orbitals, one 2s and three 2p orbitals. I have no idea why they'd bother to emphasize that as it's not hard to keep track of orbitals per shell anyway, especially with a periodic table to look at.

Actually how does this number make sense "by looking at the periodic table"? For example, for the 2nd shell, how do you see 1 2s and 3 2p orbitals??? Thank you!!

 

[mcloaf]

Actually how does this number make sense "by looking at the periodic table"? For example, for the 2nd shell, how do you see 1 2s and 3 2p orbitals??? Thank you!!

Well, the left hand (alkali and alkaline earth metals) are S orbitals. 1 electron for each column fills the orbital.

On the right hand side you have the P orbitals, which can hold six electrons with two per orbital, or three P orbitals.

In the middle you have the D block elements. The block is ten wide, so with two electrons per orbital there must be five D orbitals.

I understand things better when I can see them/picture them in my head, so associating the orbitals with an image of the periodic table like this helps me keep things straight.