MO Theory: Homonuclear Diatomic Molecules - Video Tutorials & Practice Problems
Get help from an AI Tutor
Ask a question to get started.
Homonuclear Diatomic Molecules are composed of 2 identical elements bonded together.
Molecular Orbital Diagrams of Homonuclear Diatomics
1
concept
MO Theory: Homonuclear Diatomic Molecules Concept 1
Video duration:
3m
Play a video:
Now recall that a whole nuclear diatomic molecule is composed of 2 identical elements bonded together. Good example of this is n 2 or f2. Now as a result of increase in electronegativity and a decrease in atomic size, the order of sigma 2p and pi 2p will be reversed for oxygen to neon. So we take a look here at molecular orbital diagrams. In this first one, this correlates to only h two to h e two, so hydrogen and diatomic, helium, which is not a normal structure. And remember, we're looking at the valence electrons for these elements. In hydrogen and helium, their valence electrons are found in the one s orbitals or in period 1 of the periodic table. So here we have, for instance, this could be the atomic orbital of hydrogen or helium and the other hydrogen or helium. We would fill in the atomic orbitals and then distribute those electrons into our molecular orbitals here. Remember, sigma 1 s represents our bonding molecular orbital and sigma star 1 s represents our antibody molecular orbital. Now if we move to the next one, this correlates to diatomic lithium all the way to diatomic nitrogen. Here, it gets more complex because now we're dealing with period 2 elements. So we'd start off with 2 s and we move our way up to 2p. Now here with the 2 s orbitals, atomic orbitals, we fill in first our bonding molecular orbital, which is sigma 2s, and then start filling in our sigma star 2s, which represents our antibody molecular orbital. When we get to 2p, it gets more complex as the atomic orbitals continue to pull their electrons together to create new molecular orbitals. Here the order for it would be pi 2p, sigma 2p, then it'll go pi star 2p, which is an antibody molecular orbital, to sigma star 2p, another antibody molecular orbital. Again, we always fill from lowest molecular orbital up. Now again because of increase in electronegativity and a decrease in atomic size, we're gonna have a slight change when it comes to diatomic oxygen to diatomic neon. If we look, the change happens here. They flip, so now my pi 2p moves up, and my sigma 2p moved down. So here again, oxygen to neon, there's still period 2 elements, so we're starting out with 2 s again, and we just start pulling together our atomic orbital electrons and dumping them into our molecular orbitals and start filling it up as we move up. So So just keep in mind, these are the different types of molecular orbitals that can exist based on what type of period element you're dealing with, 1, 2, or 3. Alright. So keep this in mind as we start doing more and more questions dealing with homonuclear diatomic molecules.
2
example
MO Theory: Homonuclear Diatomic Molecules Example 1
Video duration:
3m
Play a video:
Using a molecular orbital diagram or MO diagram, write the electron configuration for the difluorine anion, f two minus 1. Alright. So let's follow the steps. Step 1, we need to determine the number of valence electrons that this particular anion possesses. Fluorine is in group 7a, so it has 7 valence electrons, and there are 2 of them. So that's times 2, so that's 14 valence electrons. Minus 1 means we've gained an additional electron. So in total, we have 15 valence electrons. Step 2, we're gonna construct the molecular orbital diagram based on location of the valence electrons. Remember, if we're dealing with period 1 elements, that means the electrons start in 1 s. If we're dealing with period 2 elements, they start with 2 s, and period 3 elements start with 3 s. Now we're gonna use the molecular orbital diagrams that we have here. Now remember we're dealing with 2 fluorine 2 fluorines involved because it's f2 and it's minus 1. So remember, we're gonna say it has 7 valence electrons, So that'd be up, down, up, down, up, up, up, so that's 5, 6, 7, up, up, up, and then there. But remember we have one additional you can put it in on either one. So we'll put it here for that additional electron. Now we would just pull those electrons together into our molecular orbitals. So here we have up, down, up, down, up, down. So that's 2, 4, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15. So this will represent the molecular orbital diagram for the difluoron fluorine anion. Now here we've filled in the total number of valence electrons for each element into the molecular orbitals. And now to fill in our electron configuration, it's a little bit different. So the way we do it is we show each one of our molecular orbitals as individual things here within parentheses, and up here we put the number of electrons found in each. So if we look, we have 2 electrons within the sigma 2 s orbital, 2 electrons in sigma star 2 s, 2 electrons within sigma 2p, 4 total electrons within pi 2p, 4 total electrons within pi star 2p, and then finally, 1 electron within our sigma star 2p. So those are the numbers we placed down here. Alright? So we're gonna come back down here and we're just gonna fill them in. Right? So what did we say here? We said we had 2 electrons here, 2 electrons here, 2 electrons here, 4 and then we had if we come back up here, we had 4 in pi 2p, 4 in pi star 2p, and 1 in sigma star 2p. Okay. So come back down here, make sure we fill them in correctly. So 4, and then finally here we have 1. So this would represent the filled in molecular orbital electron configuration for our difluorine anion. So again, this is the approach you would take in terms of filling out the molecular orbital for your designated diatomic molecule or ion, and then you would set up your molecular orbital electron configuration in this fashion, and and fill in the number of electrons found within each particular molecular orbit.
3
Problem
Problem
Determine the number of electrons found in the π2p orbitals for the dioxygen dication, O22+.
A
2
B
0
C
4
D
3
4
Problem
Problem
Using a MO diagram, write the electron configuration for the P2 molecule