CHEMISTRY COMMUNITY

Hailey Kang 2K

Hi!

Discussion sections still take place unless yours is this coming Monday.

Hailey Kang 2K

Hi!

I don't think we have to worry about that for this unit at least. One of the UAs went over it in their session, but it isn't super relevant for now.

Hailey Kang 2K

The only things that are graded in this class are chem community, Sapling, and the exams! Everything else is just for your benefit.

Hailey Kang 2K

Hi!
In terms of solving the problem, I would probably agree with the people that have already posted. But on a side note, #7 actually isn't in the list of problems he assigned us to do so we might not even be expected to know this exact problem!

Hailey Kang 2K

Hi!

I would imagine that that was probably a calculation error. I think the numbers on sapling are different for everybody, but at least for mine, I didn't end up getting any negatives under the root!

Hailey Kang 2K

Hi!

I think Dr. Lavelle mentioned during lecture that not too many concepts from 14A would carry over. I've heard 14B has more calculations!

Hailey Kang 2K

Hi!

M refers to molarity which is the same thing as mol/L

Hailey Kang 2K

Hi!

If you get 2 positive numbers, you should omit the one that is larger than any of the given initial conditions. Generally, you will use the smaller positive number.

Hailey Kang 2K

Hi!

You need to access Sapling through CCLE in order for it to work. In terms of the code, if you purchased multi-term access, they should have sent you 2 codes (one that you can enter for this quarter).

Hailey Kang 2K

Hi!

During 14A, they were only posted for the first unit. I'm assuming this it just because of time and because Dr. Lavelle is giving us a chance to get ahead before the quarter starts.

Hailey Kang 2K

Definitely something that worked for me this quarter was going to all the UA sessions, so that's one thing I will continue next quarter! Also like you said, utilizing the textbook and reading all the information there :)

Hailey Kang 2K

Hi! A simple way to look at the trend is that metalloid band plus a few more atoms around it will form amphoteric compounds. If it's difficult to tell based on this, you will need to look at if it can accept as well as donate a proton.

Hailey Kang 2K

Hi! Only one of the lone pairs can bond to a central atom.

Hailey Kang 2K

Hi! Electronegativity increases up and to the right. Therefore, Cl will be higher. Also, electronegativity refers to the atom's tendency to attract electrons. Since Cl has 7 valence electrons, it really wants to attract one to complete its octet. This means electronegativity will be higher.

Hailey Kang 2K

Hi!

This is possible because when the principle quantum number is n=6, all the l values can be 0-5. l=3 means the f subshell, which is where you would get the 6f.

Hailey Kang 2K

Hi!
The main elements we definitely have to know for this class are P, S, and Cl. Other than that, anything with a d-orbital can have an expanded valence.

Hailey Kang 2K

The coordination number just refers to the number of points at which ligands are attached to the central metal atom!

Hailey Kang 2K

Hi! Everything with polydentate ligands is considered a chelating compound.

Hailey Kang 2K

The hybridization is sp3 because there are 4 regions of electron density (3 bonding pairs and 1 lone pair). 4 regions of electron density corresponds to sp3 hybridization.

Hailey Kang 2K

Hi! The composition of the bonds would be the bond all together. So for example in this structure, there's a C single bonded to an H. The composition of this bond would be sigma(H1s, 2Csp2) because the carbon has 3 regions of electron density. The lone pair is strictly referring to that lone pair. S...

Hailey Kang 2K

Hi!

The name of the compound should be pentaamminechlorocobalt(III) chloride.

Hailey Kang 2K

Hi!

Electronic geometry takes into account all the bonding pairs as well as lone pairs on the central atom. molecular geometry only looks at the bonding pairs.

Hailey Kang 2K

Hi! Single bonds are always sigma bonds. Double bonds have 1 sigma and 1 pi, and triple bonds have 1 sigma and 2 pi

Hailey Kang 2K

Hi! yes, lone pairs affect both electronic arrangement and molecular shape.

Hailey Kang 2K

abby hyman wrote:Does anyone know if there is any way to review the ones you missed on midterm 2?

If you email your TA or go to office hours, they can discuss the ones you missed!

Hailey Kang 2K

The scores have been posted on ccle!

Hailey Kang 2K

I heard that there is a possibility grades will be released tomorrow! Either way, he will send out an email when they are posted :)

Hailey Kang 2K

Hi!

You can use shape as a good indicator as to whether a molecule is polar or nonpolar. I would say that you still need to check whether or not the dipole moments cancel, but shape is a good check as well.

Hailey Kang 2K

Hi!

Any time there's an uneven number of electrons it's a radical, so as others have said I would assume it's an error on the textbook's part.

Hailey Kang 2K

Hi!

Electron density refers to the probability that you will find an electron in that region.

Hailey Kang 2K

Hi!

l=5 would be a valid answer. Your l value can be all the number leading up to n-1. so for example, if n=5, all your possible l values would be 0,1,2,3,4.

Hailey Kang 2K

Hi!

Definitely going to as many UA sessions has been the most helpful for me. Other than that, the textbook problems/sections are very helpful.

Hailey Kang 2K

Hi!

Simply put, electrons that are delocalized are shared between atoms. Because resonance structures are a blend of all the possible lewis structures, this means that on a diagram, you can find these electrons in any position.

Hailey Kang 2K

Hi!

The midterm will cover the last 8 bullets of outline 2 as well as all of outline 3.

Hailey Kang 2K

Hi! Basically,atoms or ions with electron clouds that readily undergo a large distortion are highly polarizable. Because of this principle, anions that are large can expect to be highly polarizable. This is because the anion is so large, that the nucleus only has weak control over its outermost elec...

Hailey Kang 2K

Hi!

I don't think it has a huge affect so I believe nitrogen will still be smaller.

Hailey Kang 2K

Hi! I was wondering this also. The textbook did mention that the arrow pointing towards the partial positive atom is a modern notation, and the arrow pointing towards the partial negative atom is older. Since the example he did in class has it pointing towards the partial negative atom, I would go w...

Hailey Kang 2K

Hi!

Hydrogen bonds occur between atoms with lone pairs, but they also can only bond with Nitrogen, Oxygen and Fluorine

Hailey Kang 2K

Hi!

The difference between the two is that a dipole-dipole attraction is the force between molecules, while the polar covalent is in between atoms.

Hailey Kang 2K

Hi! How I solved it was I drew out the Lewis structures for all of them and looked at the different bonds. For multiple bonds (double & triple bonds), they are going to be "shorter and stronger".So for example, in part a, CO has a triple bond, so it will be the strongest. I will attach...

Hailey Kang 2K

Hi!

Normally when the question is asking for the most stable structure, you are going to want to find the formal charge.

Hailey Kang 2K

Hi!

One of the things that probably helped me the most was definitely attending as many UA sessions as possible. The worksheets are super helpful, but also a lot of people will ask questions that you didn't even think up but end up being super important. Textbook problems were very helpful as well!

Hailey Kang 2K

Hi!

I would say the easiest way to remember it is # of valence electrons- # of lines & dots around that element

Hailey Kang 2K

Hi!

I would definitely recommend going to the UA sessions. They have really helpful worksheets and give very detailed and helpful explanations for everything!

Hailey Kang 2K

Hi!

Dr. Lavelle said there are subshells past f but the only ones we need to worry about for this class are s,p,d,f.

Hailey Kang 2K

Hi!

The total number of electrons is equal to the atomic number.

Hailey Kang 2K

P represent momentum! The equation to find momentum is p=(mass)(velocity).Also remember to convert to SI units!

Hailey Kang 2K

Hi!

While you're solving the problem, you should always convert to meters since it is an SI unit. Sometimes the question will ask for the wavelength in other units like nm, but that should only be converted at the very end.

Hailey Kang 2K

Hi!

The Rydberg's equation only work for for Hydrogen atoms and other single electron atoms.

Hailey Kang 2K

Hi!

If the kinetic energy is equal to 0, you would set hv equal to the work function. This is because in order to remove an electron from the surface, the energy of the photon must be at least equal to or greater to the work function.

Hailey Kang 2K

Hi!

Sapling randomized the homework questions so it's hard to tell which is which. Dr. Lavelle said we definitely need to know 19 of them, so I just picked out the 19 questions with topics that we have learned.

Hailey Kang 2K

Hi!

For the midterm, I would recommend using exactly what is on the constants and equations sheet. Since the test is multiple choice, I'm sure all the answers will be rounded, but you will get a more accurate answer that way.

Hailey Kang 2K

Hi!
I would definitely memorize some of the wavelengths such as:

Balmer series (visible light): 700nm-400nm
Lyman series (Uv region): less than 400nm
Infrared region: greater than 800nm

Hailey Kang 2K

Hi!

The first thing you need to do is calculate the energy with the equation E=hc/lambda. Then, because it is asking for the photons required to absorb a specific energy, you will do the given energy divided by what you just solved.

Hailey Kang 2K

Hello! The first thing you need to do is solve for the energy of one photon, which you can do through the equation E=hc/λ. After that, you divide the given energy by the one that you found and that should give you the correct answer. I think everybody's numbers are different but I can attach my work...

Hailey Kang 2K

Hello! I'm going through this textbook example Screen Shot 2020-10-18 at 4.10.47 PM.png Screen Shot 2020-10-18 at 4.10.47 PM.png In the explanation, it says that the uncertainty in the speed is 2(1.0e-3m/s) and I was wondering where the 2 is coming from, or why you would multiply that by 2. Thank you!

Hailey Kang 2K

Hi!
In the Balmer series, the excited electron will go to level 1 (n1), and in Lyman it will go to n2. One way you can figure out which series it is is by looking at the wavelength. The Balmer series will be the visible region (700nm- 400nm) and the Lyman will be the UV region (less than 400nm)

Hailey Kang 2K

Hi! In general, the visible light range is 700nm-400nm. Because the red light is 656.3nm, we can infer that it is within the visible region. According to the Balmer series, the starting level for visible light is n=2. This means in the Rydberg equation, n1 will be equal to 2, and then you can use th...

Hailey Kang 2K

hope this helps!

Hailey Kang 2K

Hi! When you are asked to find the molecular formula, the molar mass of the compound will be given (which is found through mass spectrometry). You need to calculate the molar mass of the empirical formula, and divide the given molar mass by the one you found. If they do not equal each other, you kno...

Hailey Kang 2K

Hi! Avogadro's number (6.022e23) basically represents the number of "things" (molecules, atoms, compounds) per mole of a certain substance. The explanation from the textbook says, "exactly 12 g of carbon-12 corresponds to exactly 1 mol of carbon-12 atoms.", so essential there are...

Hailey Kang 2K

Hello!

Thank you so much for this! I'm not sure if this was already asked, but how long would you say you studied for the MCAT before taking it?

Thank you!

Hailey Kang 2K

Hi! When balancing an equation you have to look at the total number of the individual moles. Each side of the equation does not necessarily have to have the same coefficients. In this example, you have 2 Na on each side, 4 H on each side, and 2 O on each side. This means the equation is balanced. Ho...

Hailey Kang 2K

Hi!

He said that they should all be completed before week 2, and he also said that we should finish the fundamentals by the end of week 1.

Hailey Kang 2K

Hi!! When it says AgCl precipitates out, it essentially just means that it is a product of the reaction. To find the mass, you first balance the equation, and then find the molar mass of C6H9Cl3, AgNO3, and AgCl using the ratios found in the balanced equation. Then you divide each of the given masse...

Hailey Kang 2K

I was wondering if someone could help me with the Week 1 Sapling homework question 10.

I'm unsure of how to start it off.
Thank you!

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