CHEMISTRY COMMUNITY

Nancy Yao

It's been said that people learn things faster under pressure! Don't give up! :D

Nancy Yao

Just count them! :)

Nancy Yao

I am deciding between renting an apartment or living in the dorm

Nancy Yao

I am looking forward to make more friends at UCLA and hanging around in LA!

Nancy Yao

Exercise your body and mind. ---Professor Lavelle

Nancy Yao

I am very stressed and burnt out now, but I still take more courses next quarter to challenge myself :(

Nancy Yao

I use handwriting to help myself remember and understand things.

Nancy Yao

So many people are advocating for Organic Tutor! I am gonna have a try.

Nancy Yao

Email your TA! I agree with that.

Nancy Yao

I think 50 points is not divided weekly, as long as you make enough posts before the closure of chemistry community.

Nancy Yao

I am worried about my grades too this quarter. You are not the only one!

Nancy Yao

If you pass the class, you won't be able to retake it, but honestly I wouldn't sweat it too much. Your GPA is definitely important, but it doesn't define you obviously. I would say it's more important that if you do choose to continue on the series, you do your best to do better in 14C and CL. If y...

Nancy Yao

Only one, CSPF.

Nancy Yao

Have a lot of sleep!

Nancy Yao

Beethoven sonata "Tempest"

Nancy Yao

The Story of a Stone, or Dream of the Red Chamber

Nancy Yao

Game of Thrones definitely

Nancy Yao

spaghtti

Nancy Yao

Strawberry mango smoothie

Nancy Yao

Sushi!

Nancy Yao

Matcha ice cream!

Nancy Yao

I am already exhausted after midterm 2

Nancy Yao

My grades on midterm 2 looks so bad

Nancy Yao

Do some past paper

Nancy Yao

Attend the workshop sessions

Nancy Yao

Also do the textbook problems

Nancy Yao

Doing some workshop problems will help

Nancy Yao

Gosh I am so stressed about this.

Nancy Yao

Gosh I am so stressed about this.

Nancy Yao

Gosh I am so stressed about this.

Nancy Yao

Gosh I am so stressed about this.

Nancy Yao

I am so stressed about this

Nancy Yao

I am so stressed about this

Nancy Yao

I am so stressed about this

Nancy Yao

I am so stressed about this

Nancy Yao

I am so stressed about this

Nancy Yao

50 points are enough.

Nancy Yao

Ah that's so true. The midterm problems are so tricky.

Nancy Yao

CH3NH3Cl is an ionic compound, consisting of CH3NH3+ and Cl- ions. The overall salt does not donate protons, the CH3NH3+ ion does (to form H3O+) when the salt is dissociated in water. Cl- is a very weak conjugate base so its basicity is negligible. Therefore the salt is acidic because of CH3NH3+, a...

Nancy Yao

Does anyone know how to solve 2.c of Matthew's week 1 worksheet? I tried many times but still get 337.7, while the answer is 6.96M.

Nancy Yao

Also, could you post the week 4 practice sheet to the folder? I cannot find it. Thanks!

Nancy Yao

Hi, could you post the answer sheets to your previous workshops? Thanks!

Nancy Yao

They both will lead to the same outcome of the species being protonated. I would try not to confuse yourself with the changing pKa or pKb. If it said that the salt reacted with water then you have to change it to account for hydrolysis but in this case you will still get that the protonated species...

Nancy Yao

First we shall determine what state the chemical will be in, protonated or neutral. For this we have to look at the pKb and pH. If the pH < pKb, then the protonated species will be more prominent. The chemical is in a more acidic environment which means that there is a higher [H+] present. Rather t...

Nancy Yao

K is a more general term while Kc refers to the concentration of reactants and products

Nancy Yao

Does anyone know how to solve this question?

Nancy Yao

First, watch this video: [youtube]https://www.youtube.com/watch?v=50tT_jdkINw[/youtube] It helps a lot. But I'll still explain. First calculate the volume(mL) of NaOH needed, which is 50.51082959mols from this: 7.416\cdot10^{-3}\cdot\frac{100}{1.4682\cdot10^{-2}} . So you now have the mols of NaOH ...

Nancy Yao

That part of the lecture was talking about how you can convert between partial pressures and concentrations for gases. PV=nRT is the ideal gas law. If we rearrange it to P=\frac{nRT}{V} , we notice that n/V is just concentration ( M=\frac{mol}{L} ). Therefore, if we ever need to convert partial pre...

Nancy Yao

Ivy Tan 1E wrote:
305405193 wrote:Do any of you have any recommendations on a good YouTube video for explaining Ice tables?

Hi!
https://youtu.be/aJ0KNQ5-KaI here's a short video describing how to use ICE tables using an example. Hope this helps you!!

It helps so much! Thanks!

Nancy Yao

This topic sounds to be very hard

Nancy Yao

Rachel Kho Disc 2G wrote:Also will we need to have the formula that converts Kc to Kp memorized? Or will that be given to us on an equations sheet?

Isn't that equation is PV=nRT?

Nancy Yao

Thanks! This helps so much.

Nancy Yao

Thanks for your post!

Nancy Yao

Annika Tamaki 1E wrote:You have to click the use credit option. It didn't work for me yesterday, but I tried it again today and it went through. So if it doesn't work for you, I'd say wait a day :) hope this helps!

It helps so much! Thanks!

Nancy Yao

I also have similar problems. My problem is that the lectures sometimes takes a long time to load and it often stops for loading. I am really grateful to see so many recommendations on learning resources.

Nancy Yao

I barely finished the exam. I rushed on several questions and I am pretty sure they are wrong. Also, I did wrong on questions that I spent a lot of time on, which is quite disappointing.

Nancy Yao

I am going to travel around.

Nancy Yao

Joyce Pang 2k wrote:Hibernation.

Haha

Nancy Yao

Just do more practices.

Nancy Yao

Yes, the s-character is quantified just as you explained it. In terms of question 2F.15, it means that bond angle will increase as s-character increases, as an sp2 orbital has 33% s-character, while an sp3 orbital has 25% s-character. Thank you for your help! I don't remember learning about this in...

Nancy Yao

I think it is correct.

Nancy Yao

Why is the shape of S_{2}O_{3}^{2-} tetrahedral? I drew a trigonal pyramidal shape and find that also works, which has a S-S bond in the center, and 2 oxygen bind to one S and 1 oxygen binds to the other S, but I googled after the exam and found that the shape is tetrahedral.

Nancy Yao

Michelle Magana 2B wrote:T shape molecular geometry has <90 degree bond angles. I also attached a chart which you can refer to.

This chart helps so much!

Nancy Yao

In VSEPR theory, the lone pair forces the molecular geometry of SF4 into a see-saw shape. Two of the S-F bonds are pointing away from each other, and their bond dipoles cancel. But the other two S-F dipoles are pointing "down". Their bond dipoles do not cancel, so the molecule is polar.

Nancy Yao

1 lone pair to form 1 bond: monodentate
2 lone pairs to form 2 bonds: bidentate ligand
3 lone pairs to form 3 bonds: tridentate ligand
6 lone pairs to form 6 bonds: hexadentate ligand

Nancy Yao

It can have multiple ligands.

Nancy Yao

For those textbook problems, I drew out the Lewis structures and looked for atoms that had lone pairs. For example, for water, the oxygen has lone pairs, so it can be a monodentate ligand (it's not a bidentate ligand because the two lone pairs are on the same bonding site). At the UA session earlie...

Nancy Yao

Tetrahedral is represented as AX4, while square planar is AX4E2, as square planar has two more electron domains. Prof Lavelle said this shape is not common at all, like XeF4, but in Sapling it says square planar is a common shape. This is why I am confused.

Nancy Yao

I only remember Dr. Lavelle going over Cisplatin-- do we have to know others? I'm pretty sure the only one we'd have to know is cisplatin, and possibly why transplatin is its ineffective counterpart. I know for transplatin it is ineffective because of the geometry (correct me if I am wrong). Cispla...

Nancy Yao

I'm assuming you meant [Co(CN)5(OH2)]2-. For that, the name would be Aquapentacyanocobaltate (III) Aqua comes first alphabetically. Then cyano and we have to add penta- because there are 5. After that, we add the transition metal name and add -ate because the complex is negative. Add the charge of ...

Nancy Yao

K has a positive charge of 1 and en is neutral, CN has a negative charge of 1 and there are two of them, so Cu has to be +1

Nancy Yao

I am confused how to determine the charge of each specific ligand, like Cl, NH3, H2O, NH2, etc.

Nancy Yao

H2O also has two lone pairs but it is a monodentate as well. I read some explanations online and they say that it is because water only has one donor atom and in polydentates there are more than one donor atoms. The other lone pair on the same atom cannot bond to the metal due to geometrical reasons.

Nancy Yao

Heme complex is formed when a Fe is bound to a porphyrin ligand, and the porphyrin ligand is a cake-like molecule, a tetra dentate in the shape of square planar with 4 nitrogens.

Nancy Yao

I completely ignored this part in the lecture, thank you for posting this!

Nancy Yao

It did appear in the exam and I did it wrong highly possibly.

Nancy Yao

H-Cl bond is longer than H-F bond because Cl has larger atomic radius than F, so it is easier to break. Strong acid loses H+ more easily, and also the resulting anion is stabler. For HClO, the Cl in the Cl-O anion delocalize electron to a larger degree than Br in Br-O, and therefore HClO has greater...

Nancy Yao

Prof. Lavelle posted picture of the diagonal band of metal oxides in the periodic table.

And besides these metal oxides, I only know there is H_{2}PO_{4}^{2-}

Nancy Yao

Dear Prof. Lavelle,

Thank you for explaining the concepts so well. You did a great job talking about the links to further knowledge in physiology, pharmacology, medicine, etc. Also, thank you for your support during this time of difficulties.

Nancy

Nancy Yao

Do some massage :)

Nancy Yao

Strong Acid + Strong Base -> neutral salt

Strong Acid + Weak Base -> acidic salt

Strong Base + Weak Acid -> basic salt

Nancy Yao

Thanks for the videos!

Nancy Yao

I think it is like this too.

Nancy Yao

Write it in a straightforward way:

single bond = sigma-bond
double bond = sigma-bond + pi-bond
triple bond = sigma-bond + 2 pi-bonds

Nancy Yao

Hydrogen bonding can happen only when the hydrogen is in a polar molecule and the other atom in the hydrogen bonding is electronegative (N, F, O).

I think in this case, water would prefer to form hydrogen bond within itself rather than hydrogen bonding with H2S.

Nancy Yao

Francesca_Borchardt_2L wrote:I know for midterm 1, my TA had us set up appointments to go over the midterm with him. I am assuming the same is going to happen for Midterm 2 too.

Thanks! That helps so much. I also want to go over midterm 2.

Nancy Yao

Besides the general trend s<p<d<f, electrons enter 4s orbital before 3d because the 4s is initially Lower in energy. From Scandium (Sc) onwards, the 3d orbital becomes Lower than 4s.

We write 3d before 4s in configuration, like K [Ar]4s1, Ca [Ar]4s2 with no 3d orbitals

Nancy Yao

chinmayeec 3L wrote:Dr. Lavelle sent an email saying that students must keep scheduled Chem 14B class time open because we will have tests during class time. So yes, you shouldn't overlap it with another lecture.

Hope that helps!

It helps so much! I missed that email.

Nancy Yao

https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14A/Final_Review_Sessions_14A.pdf

Final 11:30am – 1pm, Sunday December 13.
Alternative time for international students, 8pm – 9:30pm, Sunday December 13.

Nancy Yao

December is so intense.

Nancy Yao

The shortcut I use is that: if an atom forms more than one bond with another atom, then there are e- in unhybridized orbitals. This is because the energy level difference between, for example, 2p and 2sp2 is smaller than the energy of e- repulsion. The unhybridized orbitals (perpendicular to 2sp2 o...

Nancy Yao

sigma-bond: 2 orbitals, each with 1 electron, interact end-to-end to form 1 sigma-bond, allow bond atoms to rotate, resulting sigmabond has electron density with cylindrical symmetry around internuclear axis pi-bond: p orbitals overlap side-by-side, do not allow atoms to rotate (rigid), and the elec...

Nancy Yao

My high school chemistry teacher recommended us to write down everything you know on a blank sheet of paper, and this process will help you recall the knowledge you gained, especially the bulky parts, like the chart of different chemical geometries and their bond angles, or the elements that do not ...

Nancy Yao

The dipoles are like vectors and sometimes they cancel out each other.

Nancy Yao

The names of the chemicals in problem 2E.4 are (a) SeF6 (b)IF7

Nancy Yao

I slept through Thanksgiving but it is still fun :)

Nancy Yao

I would say first draw the Lewis structure and determine the number of lone pairs, and then determine its shape. The existence of lone pairs explain the difference between trigonal planar and trigonal pyramid and between tetrahedral and square planar, and both pairs of shapes have the same coordinat...

Nancy Yao

Below are the several shapes we've learned in class: Coordination number 2 (not very common): linear, bent Coordination number 3: trigonal planar, trigonal pyramid Coordination number 4: tetrahedral, square planar Coordination number 5: trigonal bipyramid Coordination number 6: octahedral After iden...

Nancy Yao

Here is a person who did not post anything on chemistry community until week 9 and is also worried about passing the course :(

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