1. Ground configuration: 1s2 2s2 2p4 .
QUESTION:
How many electrons are unpaired in the ground state of Oxygen? A. 0, B. 1, C. 2, D. 3
Oxygen has 8 electrons
Ground configuration: 1s2 2s2 2p4 .
Hund’s Rule of maximum multiplicity: to get the ground state --- when filling a subshell with more than one orbital, fill singly, parallel spins before pairing up
SCRIPT:
How many electrons are unpaired in the ground state of oxygen?
0…. 1…. 2…. Or 3
PAUSE CLICK
Oxygen has 8 electrons. So its ground configuration is 1s2 2s2 2p4.
Let’s look at this configuration in more detail using what’s called an orbital diagram
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In the orbital diagram shown here, each box represents an orbital.
Note that there is only one orbital in the s subshells.
The first two electrons go to the 1s orbital. Note that Pauli’s exclusion principle requires that the electrons have opposite spins. We represent the electron with spin up using an upward pointing arrow.
And we represent the electron with spin down using a downward pointing arrow.
The next two electrons to go the 2s orbital. Again, one spin up
And the other … spin down
The next four electrons go to the 2p orbitals, but which ones?
Quantum theory says that all three orbitals in the p subshell are equivalent, electrons should not have any preference for any one.
In this case, there are, in fact, 15 different ways of distributing the four electrons among the 2p orbitals, keeping in mind that …
if we put two electrons in one orbital, they must have opposite spins.
It also turns out, that at a more accurate level of quantum theory, which is beyond the scope of a general chemistry course, some of
these fifteen ways are more stable than others To get one of the most stable ways, we can use Hund’s Rule of maximum multiplicity.
Hund’s rule says that to get the ground state,…. The most stable state…when filling a subshell with more than one orbital, we fill
The orbitals singly first, with electrons of parallel spin before we pair up electrons. Here’s one way we can do.
Remember, we four remaining electrons electrons to distribute among the p orbitals.
We put an electron with spin up in one of the p orbitals.
The next electron needs to go another orbital, also with spin up.
And since there is another empty orbital left… the next electron goes there, also with spin up.
We’ve got one electron left. It can go to any one of the three orbitals. But it must have an opposite spin.
It can go here…CLICK
Or here… CLICK
Note that we could have put in the first three electrons spin down instead of spin up. If we did, then we’d have to put the last electron spin up. It doesn’t really matter.
Going back to the question,… how many electrons are unpaired in the ground state of oxygen?
The answer is two.
PAUSE 2 seconds
END RECORDING

2. Video ID: © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08