That there is a bit of a physical chemistry lecture. This is looking like an introduction to molecular geometry (how the atoms orient themselves in a bond with others) and orbital theory. The second is basically just a way to mathematically explain the way the atoms' electrons behave in a bond.
The notations around it are related to the molecule in three dimensions. If the left two hydrogens are wishboned off of the first carbon in the plane of the blackboard, then the right two hydrogens would be wishboned into and out of the plane of the blackboard.
It's some sort of hybrid orbital stuff, from the Phosphorous on the side. The only cryptic stuff seems to be the P-sub-x and P-sub-y under the hydrocarbon. Maybe I learned it in different notation.
@7 This isn't the first week of class anymore. They should have moved long beyond orbitals by this point in the term, and should be doing Michaelis-Menten kinetics type-stuff by now.
Dan, there is another writer at the Stranger you should be asking. I believe you had him on your show once. He goes by the bold title of Dear Science: Seattle's only Scientist.
@15: Perhaps that notation would usually be pi_x and pi_y,. for overlapping orbitals? Seems like that would make sense in context.
The bit on the right appears to be sp2 hybridization, which is one of the various ways a chemical reaction can take place - trading one atom for another demands certain geometric restraints (the new atom has to enter from a direction that makes sense), and sp2 is one of those setups.
Yeah, those are just two example molecules to talk about the orbital paths of different electrons.
I was watching a documentary on Fermilab the other day and they through up a huge list of electron orbits on a chalkboard and I had some major flashbacks. Somewhere in my brain, all of that knowledge still exists (little-known fact, I was a chemistry major in college).
I go to WashU (great lecture by the way, loved it. Esp that bit against monogamism at the end.) I'm pretty sure there was a TA review before you and probably had to review something for a General Chemistry class.
It's too late in the semester for the material to be covered by organic chemistry or physical chemistry
It is Organic chemistry (carbon molecules = organic). It is an explanation of the types of bonds formed between the atoms (how the electrons are shared) and what the bonds would look like in 3-D space.
Based on limited high school science, this is what I came up with: The x, y, and z represent how a molecule is configured in space due to the various attractions/repulsions of the atoms and their electrons. The left cluster shows C3H4 with the double lines between the C's representing a covalent bond with each other. Carbon has 4 of 8 valence electrons filled, and must fill the other 4 spaces by sharing. The carbon on the left fills its 8 electron spaces by sharing 2 with the carbon next to it and forming a bond with the 2 hydrogens which contribute 1 electron each. The covalent, shared bond is represented by the double line and the ionic bond with hydrogen is represented by 1 line. The right cluster shows the molecule PH5, which is highly unstable because P only needs 3 more electrons to be stable. The attraction between the Hydrogen molecules is greater than the attraction between the Hydrogen and the Phosphorous. I'm assuming the squiggly lines are meant to represent this instability. The + above the phosphorous is meant to contrast the - of the Hydrogen. The sp2 describes the different types of hybridization for carbon. Maybe someone that's a science major and not an English major like I am can explain the rest?
@28 - The squiggly lines represent a bond whose geometry has it going into the board. The triangular shapes between atoms (including the weird semicircular one on P) represents bonds going out of the board. The point of the left figure (allene) is to show that the leftmost hydrogens are in the plane of the board because of their pi bonding using just the p_y orbitals of C1 and C2. The rightmost H atoms go into and out of the board because their pi bonding using the p_x orbitals of C2 and C3. The result: The hydrogens are not in the same plane! I'm not totally sure what the point of the figure at the right is. Probably something indicating that the three hydrogens all in the xy plane are experiencing bonding with sp2 hydbridized orbitals of the central P. The lowermost H would be bonded with the p_z orbital. Throw in a d orbital and you can bond the H on top, but otherwise it can be considered to be attracted through charge. My guess: this is from a general chemistry course or organic. If this was from a more advanced course (Physical Organic Chemistry, Advanced Inorganic Chem, etc.), I would expect some more depth to the diagrams, i.e. the figure at left is D_2d symmetry.
What 30 said. The Py's and Px's and sp2's are not the same as the P in the middle of the H's though. That's a phosphorus atom. C's are carbon. H is hydrogen. The other Py-Px-sp2 all have to do with how the atoms are bonded with each other. The H with the minus sign floating above the phosphorus isn't really bonded like the other hydrogens. It's mostly just attracted (opposites attract) to the phosphorus atom, which is positive because all the hydrogens it's bound to are sucking it's negativity from it.
And the lines are bonds in the plane of the chalkboard. The squiggles go backward, the triangles come forward. It's all very 3D, because we are 3D, and these molecules make us up.
This only really matters if you're into chemistry or wondering why we all don't just fall apart into the basic units of the universe.
Chemistry professor here, chiming in (very late) to say that given the point in the semester, this is certainly from a general chemistry lecture/recitation, NOT organic or physical. (Unless there's a special major at UDub that doesn't require the students to learn any chemistry beyond a freshman level)
As other commenters have pointed out, it's about hybrid bonding. On the left, the Px+Px shows that the second CC double bond is oriented up and down on the board, while the Py+Py shows the second double bond oriented out of the board - that's why the hydrogens are oriented the way they are (i.e. in a plane perpendicular to the orientation of the double bonds). The CH bonds in the allene are indeed sp2 hybridized, meaning a combination of a spherical s orbital and two oriented p (peanut-shaped) orbitals.
The sp2 on the diagram on the right shows that the 3 hydrogens in the plane coming out of the board are s hybridized with px and py, while the axial hydrogen forms a single bond with the vertical pz orbital. Add the hydride (H-) and you get a hypervalent compound where one bond is shared between two PH "bonds."
Summary: it's an attempt to explain to freshmen why molecules are shaped the way they are.
The professor is right about what s/he was saying except a few things. 1. This is an Organic problem. In general chemistry it is an introduction to chemistry for students who have not taken or not familiar with chemistry. ANY University chemistry department would be able to tell you that. If the students at the university that you teach are doing this at an entry level then more props to you all for selecting students that are extremely familiar with the basics in chemistry and do not have to start from scratch. That simply means that you have an outstanding chemistry students. 2. As a professor why would you be so negative toward other universities and not even take the time and appropriately type the name of another university
@1- Physical chemistry usually refers to thermodynamics, and this doesn't seen to be thermodynamics.
Looks like coordination chemistry to me. Either that or some sort of hybrid course with organic chem and coordination chem.
I haven't taken coordination chem in 10 years so my knowledge of it is a bit fuzzy, but the x-y-z 3D-space is a bit of a giveaway.
The notations around it are related to the molecule in three dimensions. If the left two hydrogens are wishboned off of the first carbon in the plane of the blackboard, then the right two hydrogens would be wishboned into and out of the plane of the blackboard.
@7 This isn't the first week of class anymore. They should have moved long beyond orbitals by this point in the term, and should be doing Michaelis-Menten kinetics type-stuff by now.
how you like dem apples, etc
The bit on the right appears to be sp2 hybridization, which is one of the various ways a chemical reaction can take place - trading one atom for another demands certain geometric restraints (the new atom has to enter from a direction that makes sense), and sp2 is one of those setups.
Thanksgiving: it's better with science.
The three P orbitals are generally labeled x, y, and z. SP2 hybridization will only utilize two of the three (x and y).
And yeah, this is mid-quarter majors-level intro to general chemistry. :)
I was watching a documentary on Fermilab the other day and they through up a huge list of electron orbits on a chalkboard and I had some major flashbacks. Somewhere in my brain, all of that knowledge still exists (little-known fact, I was a chemistry major in college).
It's too late in the semester for the material to be covered by organic chemistry or physical chemistry
=)
And, she would make it clear that she knows ...
Change in the air
And the lines are bonds in the plane of the chalkboard. The squiggles go backward, the triangles come forward. It's all very 3D, because we are 3D, and these molecules make us up.
This only really matters if you're into chemistry or wondering why we all don't just fall apart into the basic units of the universe.
[/snarkasm]
As other commenters have pointed out, it's about hybrid bonding. On the left, the Px+Px shows that the second CC double bond is oriented up and down on the board, while the Py+Py shows the second double bond oriented out of the board - that's why the hydrogens are oriented the way they are (i.e. in a plane perpendicular to the orientation of the double bonds). The CH bonds in the allene are indeed sp2 hybridized, meaning a combination of a spherical s orbital and two oriented p (peanut-shaped) orbitals.
The sp2 on the diagram on the right shows that the 3 hydrogens in the plane coming out of the board are s hybridized with px and py, while the axial hydrogen forms a single bond with the vertical pz orbital. Add the hydride (H-) and you get a hypervalent compound where one bond is shared between two PH "bonds."
Summary: it's an attempt to explain to freshmen why molecules are shaped the way they are.
Washington University is not called UDub. It's Wash U, Washington University, or Washington University in St. Louis if you want to be formal.