CHEMISTRY COMMUNITY

Victoria Li 1L

Geometry refers to the arrangements of regions of electron density around an atom (a.k.a. coordination number; lone pairs + bonds). Shape doesn't account for lone pairs.

Victoria Li 1L

I think we're expected to know these special cases. Another one that comes to mind is ferrate, but the other transition metal names should be more straightforward!

Victoria Li 1L

Shape (& kind of bond angles)! Different molecule shapes have different planes. For example, trigonal planar atoms are all in the same single plane (120 degrees apart). However, octahedral molecules have 4 equatorial atoms in one plane, and the 2 axial atoms in another. I would try to imagine th...

Victoria Li 1L

I think it's just to make the name less confusing. Both oxalato and aqua are multi-atom ligands so they might just sometimes be in parantheses.

Victoria Li 1L

The answer key says the solution is actually more acidic! The equation it has is Cu(H₂O)₆³⁺ (aq) + H₂O (l) ⇋ H₃O⁺ (aq) + Cu(H₂O)₅OH⁺ (aq)

Victoria Li 1L

First, if you haven't memorized the ligand list Dr. Lavelle posted, do that! The ligand names are the basis of coordinate compound nomenclature, and you'll know they're ligands if they're inside the brackets. Second, I would re-familiarize myself with the prefixes (di-, tri-, tetra-, etc.). Then, wh...

Victoria Li 1L

A simple way to think about it is the number of hybrid orbitals = the number of regions of electron density (e.g. 3 bonds + 1 lone pair = 4 regions). And it basically goes sp, sp2, sp3, sp3d, sp3d2 etc. sp means two regions, sp2 = 3, sp3 = 4 etc.

Victoria Li 1L

Dr. Lavelle just sent an email saying that he'll go over the last examples at the beginning of Wednesday's lecture, so I'm assuming that's the last bit of content left. Afterwards, it's just going to be review.

Victoria Li 1L

I was wondering about this too. Should it be six electrons?

Victoria Li 1L

You're right actually! It should be O2sp 2 , my bad. And for the double bonded O: iirc it wants to make sigma bonds first, so its stabler hybrid orbitals are used in making the sigma bond. The pi bond is then formed with the leftover unhybridized 2p orbital. This happens because the electron wants t...

Victoria Li 1L

I think we would probably turn it in along with next homework!

Victoria Li 1L

A strong Bronsted acid is one that is more readily to donate a proton, while a weak Bronsted acid is less willing to give up its proton(s).

Victoria Li 1L

I would assume so! He spent a good portion of lecture discussing all the rules, and Outline 5 says "be familiar with the rules for naming coordination compounds."

Victoria Li 1L

No, you're right. The solutions guide says that they're all diamagnetic (paired electrons)!

Victoria Li 1L

Axial atoms are removed first only for molecules with octahedral electron geometry i.e. 8 regions of electron density. This is because this particular arrangement minimizes electron-electron repulsion, especially if there are two lone pairs (they'd be on opposite sides of the molecule). However, eq...

Victoria Li 1L

I would imagine so - I feel like it would probably be on all the material we've covered since the midterm leading up to the test day.

Victoria Li 1L

Polarizing power = cation's ability to distort electron region of anion
Polarizability = anion's tendency to be distorted

Victoria Li 1L

Overall molecular polarity is determined by the net dipole, which is equal to the sum of all the individual bond dipoles (i.e. the electronegativity differences between two bonded atoms). For example, if an atom has a much stronger bond dipole towards one side, then that molecule has a net dipole an...

Victoria Li 1L

The larger the anion (in terms of atomic size), the more loosely the electrons are held by the nucleus. This allows the electrons to be more easily distorted by a cation. A greater tendency to be distorted = polarizability. In short, polarizability increases with atomic size. Hopefully this gives yo...

Victoria Li 1L

On homework problem 3F.1a and c, both molecules have all three intermolecular forces (dispersion forces, hydrogen bonding, & dipole-dipole). I was just wondering, if a molecule exhibits hydrogen bonding, does that mean they will also have dipole-dipole forces by default?

Victoria Li 1L

The configuration always goes from low to high in terms of n, so it would still be 3d¹⁰4s¹.

Victoria Li 1L

I don't think we'll have to know nomenclature until later when we'll actually be taught it! I just looked up the chemical formula for each ion and then drew the structures. As for the problem itself, halogens can expand their octet, meaning they don't necessarily form only 4 bonds. If they have 7 va...

Victoria Li 1L

A hybrid structure is an average of all the molecule's resonance forms/structures! And if the question asks to draw all the resonance forms of a molecule, which it usually does, you would just draw out each form (not the hybrid structure). I think we usually draw out each individual resonance form a...

Victoria Li 1L

It might not be on the midterm, but I would at least know how to write the configuration for an atom with 4f electrons (first row with f-block).

Victoria Li 1L

I think the electronegativity values would probably be given to us if it weren't obvious just using periodic trends

Victoria Li 1L

Which problems are okay for this week's homework? Can it only be from the Chemical Bonds unit or can we also do quantum problems?

Victoria Li 1L

There's a post from last year on the same topic: https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=35085

I think it has to do more with whether the atoms in question are bonded or not. However, they do have the same trend (increasing across, decreasing down).

Victoria Li 1L

It has to do with electron affinity. Atoms with lower affinities are less likely to have a stable negative formal charge because they're less likely to want to hold onto an added electron. Since electron affinity tends to decrease down a group, sulfur has a lower affinity than oxygen, and therefore ...

Victoria Li 1L

I think they're cancelled at least for today. Someone emailed one of the TAs and they said they wouldn't be happening.

Victoria Li 1L

Yep! Atoms, molecules, or ions with one unpaired electron are called free radicals. They're highly unstable and usually very reactive

Victoria Li 1L

No, someone emailed one of the TAs and they said they would be cancelled.

Victoria Li 1L

I think they're majority problem solving i.e. using equations and making calculations. However, the select questions on the homework that require explanation make me think that there might be more conceptual questions later on. The last test was mainly calculations since the content we covered was m...

Victoria Li 1L

I know it's still weeks away but I was wondering, does anyone know about the format of the midterm? Is it comparable to Test 1 but just longer in length? What types of questions will be on it and which units does it cover?

Victoria Li 1L

I think it would probably occur in groups 6 and 7 as well, in addition to some similar electron transferring in the f orbital. But like Dr. Lavelle said, we won't really have to worry about the details past Cr and Cu!

Victoria Li 1L

I don't think we need to know the orbital shapes/planes in detail enough to be able to draw them out. I agree with Brian said though - just remember that s orbitals don't have a node while the other orbitals do. That would probably be it though.

Victoria Li 1L

Yep! We're still learning content from the quantum unit this week so I would assume quantum homework works

Victoria Li 1L

I don't think so - those modules were all made at once probably a while back. They're probably just there to help us ease into the class/review some commonly confused concepts.

Victoria Li 1L

The symmetry just describes the shape of the orbitals. S the only symmetric one because it is spherical. The other orbitals have shapes that are not symmetric. Not sure what the orbital symmetry tells us though

Victoria Li 1L

Which of the following increase when the electron in a hydrogen atom undergoes a transition from the 1s-orbital to a 2p-orbital? (a) Energy of the electron. (b) Value of n. (c) Value of l. (d) Radius of the atom. Not entirely sure, but I think all of them increase because: (a) the electron must abs...

Victoria Li 1L

Does anyone know what the Sapling learning thing is? I heard it was extra practice but I was wondering how to access it/what kind of practice it was.

Victoria Li 1L

I understand that, in the case of elements like copper and silver, the s orbital electrons will donate an electron to the d orbital to achieve a full orbital. But I was wondering, why does this happen? Is a full d orbital more stable than an unfilled s orbital?

Victoria Li 1L

Amplitude isn't all that important for these calculations. However, amplitude of a wave is the same as intensity of light.

Victoria Li 1L

He said that as the energy level increased, E (the energy) decreases. Basically as n approaches infinite, E approaches zero. This is because n increasing means the electrons are moving further away from the nucleus, so the interaction between the electrons and the nucleus, E, decreases and approach...

Victoria Li 1L

During lecture today, it was mentioned that the frequency (from the E=hv equation) can't be calculated for de Broglie wavelengths since those are for electromagnetic radiation, not electrons. However, the de Broglie equation was derived from E=hv so I was wondering, do the electrons have a frequency...

Victoria Li 1L

Any de Broglie wavelength less than 10^–15 is typically not going to have experimentally detectable wavelike properties, making it more particle-like.

Victoria Li 1L

I think that light intensity is independent of the other two values. In a particle model of light, intensity is just the number of photons (e.g. higher intensity means more photons and thus more electrons ejected). In a wave model, intensity is just the amplitude. This is the post I referenced: http...

Victoria Li 1L

I think it's a good idea to include them if you can! My TA mentioned that they sometimes take off points if you don't.

Victoria Li 1L

It should be on just fundamentals!

Victoria Li 1L

I am still confused on the concept of formula units. How many formula units would be in 46g of NaCl? According to the explanations on this page, I'm assuming it would be the number of NaCl "molecules" in 46g. I put molecules in quotations since NaCl wouldn't be a single molecule in real l...

Victoria Li 1L

A formula unit is the empirical formula of any ionic solid (or covalent network solid). Since these solids (ex. NaCl or SiO2) don't exist as individual molecules, we use the term "formula unit" instead. In the example you stated, alumina is an ionic compound so the technically correct uni...

Victoria Li 1L

What exactly is the difference between formula units, molecules, and atoms? And what is a formula unit in general? How would you calculate the number of formula units given a compound's mass? For reference, this is the HW question I'm referring to (Fundamentals E) E.21 Calculate the amount (in moles...

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