CHEMISTRY COMMUNITY

madijohnson_4A

PO4 3- has resonance, so its true structure is a blend of all 4 possible resonance structures. Because of the delocalized electrons, all of the bond lengths will be the same, and be somewhere in between the single bond and double bond lengths.

madijohnson_4A

I would start by creating flashcards based on the table for naming coordination compounds he has on his class website. Once you have the common ligand names down, you just write them in alphabetical order with the correct prefixes (representing the number of each ligand), and write the metal at the ...

madijohnson_4A

As you go down a row, the bond becomes longer and therefore weaker than the bonds with elements above it. The longer bonds are due to larger nuclei, more core electrons shielding the valence electrons, and decreasing electronegativity. The longer the bond, the easier it is to break and dissociate in...

madijohnson_4A

Sigma bonds allow molecules to rotate whereas pi bonds fixate molecules in that position. Molecules with sigma bonds, therefore, are more flexible in structures.

madijohnson_4A

In question 9C.9 from the homework, why are the coordination numbers from part C and D 6?

madijohnson_4A

I feel like there will probably be polarity questions on more complicated molecules. Also, in LS 7A you need to be able to determine polarity of larger organic molecules, so even if we don't use it now, we'll need it in other classes.

madijohnson_4A

A Lewis acid is an electron pair acceptor, and a Lewis base is an electron pair donor.
A Bronsted acid gives up an H+ (proton donor), and a Bronsted base receives an H+ (proton acceptor).

madijohnson_4A

The oxidation number represents the number of electrons gained or lost by an element. For example, the oxidation number of oxygen in a compound is usually -2 because oxygen typically gains two electrons in a chemical reaction. However, the oxidation number of a neutral element is always zero (exampl...

madijohnson_4A

I would email your TA and ask if they are holding office hours next week and if you could pick it up then.

madijohnson_4A

In the Lewis structure, it looks like the electrons pairs are right next to each other, but in the VSEPR model they are much further apart with the 3D shape. For example with water, it looks like the lone pairs are right next to each other, but they are actually spaced out in the tetrahedral shape f...

madijohnson_4A

As a side note, if there are multiple bond angles within the shape (like 120 and 90 degree angles within a trigonal bipyramidal molecule), we don't have to indicate which angles go where, we can just say the angles will be less than 120 and less than 90 for a shape like seesaw with 5 regions of elec...

madijohnson_4A

I'm not sure how people do formal charge so quickly in their heads, I always need to write it out personally, but the ones I've memorized are:
double bonded oxygen with 2 lone pairs has a formal charge of 0
single bonded oxygen with 3 long pairs has a formal charge of -1
I hope this helps a little!

madijohnson_4A

He was also saying that the molecular structures involving Xenon are very rare because it is a noble gas and usually won't react.

madijohnson_4A

The Lewis structure won't show you the polarity, but it is helpful in determining the VSEPR model shape of the molecule which will then help determine polarity. If the VSEPR shape allows for dipole moments to cancel and the overall dipole moment to be zero, then the molecule will be nonpolar.

madijohnson_4A

I don't think we need to memorize exact electronegativities, but knowing the trends in electronegativity would probably be helpful to determine what bonds would be polar vs nonpolar. In general, the electronegativity increases as you move diagonally up and to the right of the periodic table.

madijohnson_4A

The best way to determine the lowest energy structure is to look at the formal charge: the closer to zero the formal charge is, the more energetically favorable the structure is.

madijohnson_4A

The nodal planes are the area where you will not find electrons- they basically just give a more detailed description of electrons within the orbital.

madijohnson_4A

Molecules with resonance are more stable because resonance spreads multiple bond character over a molecule which lowers the energy. The lower the energy, the more stable the molecule.

madijohnson_4A

I don't think we have to know anything other than the s, p, d and f orbitals so I wouldn't worry too much about it!

madijohnson_4A

The shorter bonds are double and triple bonds which share more electrons than longer single bonds. The more electrons are shared, the shorter the bonds are because there is more pull from the nuclei on the electrons. The increase number of shared electrons are what make shorter bonds stronger.

madijohnson_4A

It's probably a good idea to be familiar with the concepts by name just to be safe!

madijohnson_4A

I believe the wave function describes the height of the wave at position (x,y,z) in a field. Not sure why the wave function squared represents the probability, but I hope that helps!

madijohnson_4A

Cations have less electrons and less electron-electron repulsion compared to the parent atom, so the electrons are pulled in more by the nucleus.

madijohnson_4A

Claire Grover 3G wrote:Does anyone have the notes from lecture last Friday (10/11)? I couldn't see well from where I was sitting and want to clarify a few things. Thanks so much!

If you still need the notes from Friday I have them! Just let me know how to send them to you.

madijohnson_4A

I'm pretty sure you're right and we won't have to go past the 3d orbitals because most biological molecules stay within those first three energy levels, and the 4s orbital.

madijohnson_4A

When you work out the velocity for the electron when it is confined within the 1.7x10^-15 m of the nucleus, the velocity is 3.4x10^10 which is greater than the speed of light (3.00x10^8). The unrealistic velocity value is telling us that the electron cannot be confined within the nucleus.

madijohnson_4A

The fourth number is really just there to demonstrate that the electrons are not identical: they are spinning in opposite directions.That is why the options for ms are +1/2 and -1/2.

madijohnson_4A

In the first energy level, n=1, the only possible orbital that can be found is an s orbital with l=0 because there are only 2 electrons in available to fill the first energy level.

madijohnson_4A

I would try using the "contact us" button at the bottom of the screen and tell them about your problem because it seems very odd and like quite the nuisance. I'm sorry you're dealing with that.

madijohnson_4A

The possible values for ml are l, l-1, and -l.

When l=1, those values of ml are 1 (l); 1-1=0 (l-1); and -1 (-l).
When l=0, the only possible value of ml is 0 because 0-0=0 and -0 is also just 0.

madijohnson_4A

In order for the electron to be excited to another energy level, the incoming photon must have the exact energy difference between the energy levels. Therefore, a photon with too much energy could not be absorbed.

madijohnson_4A

Since the stoichiometric relationship between the ClO2 and BrF3 is 6:2, there should be three times more ClO2 than BrF3. Since you know BrF3 is in excess, take the amount of ClO2 (12 mol) and divide it by 3 to get the number of moles of BrF3 that should be used up in the equation (4). Then, take the...

madijohnson_4A

UV radiation is the highest energy. Everything related to n=1 is in the UV region because it takes the most energy to go from n=1 to any other energy level due to the inverse squared relationship of n in the empirical equation for the H-atom: En= -(hR)/(n)^2.

madijohnson_4A

If you go up to quick links in the top left corner of the page, there should be a section called "your posts" and that will show you all of the posts you've made. If your tenth post doesn't show up, I would make another post just in case.

madijohnson_4A

Is there a sign difference between the energy emitted versus the energy absorbed even though they are the same value? Like is the energy emitted a negative value and the energy absorbed positive?

madijohnson_4A

I don't trust atoms... I heard they make up everything.

madijohnson_4A

Was F.21 assigned in the homework?

madijohnson_4A

The net number of moles is the overall moles produced in the reaction. The way you find it is to take the moles of product and subtract the moles of reactants.

madijohnson_4A

Does Dr. Lavelle prefer rounding or truncating digits for the final answer?

madijohnson_4A

Thank you so much for your inspiring insight and story about your journey. It is really amazing to see someone who was in our shoes just a little while ago doing such amazing things. Do you have any advice for undergraduates potentially interested in medical school on when and how to study for the M...

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