Search found 55 matches

by Abril Guanes 3D
Wed Nov 25, 2020 3:58 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: H2O VSEPR
Replies: 11
Views: 28

Re: H2O VSEPR

H2O would actually be bent shape because the two electron pairs from the oxygen will push the bonds between hydrogens down, giving it a bent shape.
by Abril Guanes 3D
Wed Nov 25, 2020 3:22 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Polar and Nonpolar Bonds vs Molecules
Replies: 2
Views: 12

Re: Polar and Nonpolar Bonds vs Molecules

So polar/nonpolar bonds refer to the specific bonds within a molecule. Polar and nonpolar molecules refer to the overall molecule. So for example, H2O has polar bonds and is overall a polar molecule. On the other hand, CO2 also has polar bonds, but because the structure is linear and the dipoles can...
by Abril Guanes 3D
Wed Nov 25, 2020 11:53 am
Forum: Hybridization
Topic: Unhybridized Orbitals
Replies: 2
Views: 18

Unhybridized Orbitals

Hello! I was having trouble how to find out if an orbital is unhybridized. In his Monday lecture, Professor Lavelle would point a some part of the molecule, explaining that it did not have a hybrid orbital, and I wanted to know how you can tell that when looking at a molecule? Thank you and happy ho...
by Abril Guanes 3D
Tue Nov 24, 2020 9:09 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Sapling Question #18
Replies: 2
Views: 21

Sapling Question #18

Hello! I had a question on Sapling HW #8. The question was: "Select the correct statement about the relative positions of the hydrogen atoms in the three structures. a. The hydrogen atoms of H2CCCH2 and H2CCCCH2 lie in the same plane. b. The hydrogen atoms of H2CCH2 and H2CCCCH2 lie in the same...
by Abril Guanes 3D
Tue Nov 24, 2020 5:45 pm
Forum: Administrative Questions and Class Announcements
Topic: Chem 14B
Replies: 7
Views: 36

Re: Chem 14B

I think he means to not schedule a class at the same time as the Chem 14B lecture, because although it is recorded, he plans to have exams like midterms held during lecture time rather than discussion times. I heard some students were asking if they could double-schedule Chem 14B with another class ...
by Abril Guanes 3D
Tue Nov 24, 2020 5:18 pm
Forum: Administrative Questions and Class Announcements
Topic: Number of Questions on the Final
Replies: 1
Views: 16

Re: Number of Questions on the Final

I'm not entirely sure, but I do know that the final is 1 hour and 30 minutes instead of a typical 3 hour final. If the midterm of 50 minutes was 12-16 questions, I would assume that it would be in the mid-20 to low 20s for the amount of questions. Hopefully he'll drop info on the final soon!
by Abril Guanes 3D
Tue Nov 24, 2020 2:08 pm
Forum: General Science Questions
Topic: Sapling #8
Replies: 4
Views: 24

Re: Sapling #8

Hello! BeCl2 has polar bonds but is non polar overall. Because Be does not have any lone pair electrons the shape will be linear, so the dipoles from the Cl will cancel out. H2O also has polar bonds because the oxygen will pull the electrons from the hydrogen. The shape of H2O is bent though because...
by Abril Guanes 3D
Tue Nov 17, 2020 10:08 pm
Forum: Resonance Structures
Topic: Sapling #5
Replies: 2
Views: 11

Re: Sapling #5

First, you would want a negative charge on the most electronegative element in the molecule. Second, because carbon is the central atom, you do not want a charge on it (or any central atom for that matter) because it makes the molecule very unstable, making it unfavorable. Hope this helps!
by Abril Guanes 3D
Tue Nov 17, 2020 5:53 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Intermolecular Forces of CHI3 and CHF3
Replies: 5
Views: 31

Re: Intermolecular Forces of CHI3 and CHF3

For this example you would have to think about the size of the electronegative atoms. Fluorine, although very electronegative, is relatively small compared to Iodine. Because iodine is much larger, it has more electrons and making it more polarizable. Because it is more polarizable and has more elec...
by Abril Guanes 3D
Tue Nov 17, 2020 5:37 pm
Forum: Ionic & Covalent Bonds
Topic: matthew tran wkshop answer key
Replies: 1
Views: 53

Re: matthew tran wkshop answer key

Hello! Matthew doesn't post his answer key anywhere, he only gives out answers in the UA sessions. I'm not sure if you email him, he'll send you an answer key (as many UAs deal with past exam questions, they don't want those circulating). Regardless I found his email for you: ​mtran060@g.ucla.edu. I...
by Abril Guanes 3D
Tue Nov 17, 2020 8:06 am
Forum: Lewis Structures
Topic: Lewis Acids and Bases
Replies: 5
Views: 26

Re: Lewis Acids and Bases

Jaclyn Dang 3A wrote:Are lewis acids and bases going to be on this exam?


I saw it on the Outline 3 as a guideline. "Identify Lewis acids and bases", so I suppose so.
by Abril Guanes 3D
Mon Nov 16, 2020 10:12 pm
Forum: Lewis Structures
Topic: Lewis Acids and Bases
Replies: 5
Views: 26

Lewis Acids and Bases

Hello! Can someone help me by writing a general rulebook / guidelines for identifying Lewis acids and bases? I'm struggling with identifying them on the homework and UA sessions. Thank you in advance !
by Abril Guanes 3D
Mon Nov 16, 2020 10:10 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic and Covalent Character
Replies: 2
Views: 23

Ionic and Covalent Character

In a UA Session, we learned that "covalent character increases going down a group". This makes sense because as you go down a group, atomic radius increases and electrons are further out, allowing them to be easily distorted. However, does this apply to Groups 1 and 2? I'm confused because...
by Abril Guanes 3D
Mon Nov 16, 2020 4:22 pm
Forum: Administrative Questions and Class Announcements
Topic: MT 2 Material
Replies: 4
Views: 31

Re: MT 2 Material

Correct! The last lecture that covers Midterm II material was the one from last Wednesday.
by Abril Guanes 3D
Mon Nov 16, 2020 4:19 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Textbook 1E.17 part b
Replies: 3
Views: 15

Re: Textbook 1E.17 part b

When writing the electron configuration for Mn, [Ar]3d^5 4s^2. Although 4s subshell is filled first, when writing the electron configuration, the 4s subshell comes after because it has higher energy. This means that the electron will come off the last subshell in the electron configuration, which wo...
by Abril Guanes 3D
Thu Nov 12, 2020 7:57 pm
Forum: Lewis Structures
Topic: formal charges
Replies: 2
Views: 17

Re: formal charges

Hello! You are correct in saying that the overall formal charge is -2 as indicated by the molecular formula. When doing the Lewis structure you would want to avoid putting any charge on carbon since it is the central atom. You can do this by doing a double bond with one of the oxygens. This would be...
by Abril Guanes 3D
Thu Nov 12, 2020 2:31 pm
Forum: Lewis Structures
Topic: Oxygen and Hydrogen
Replies: 1
Views: 22

Oxygen and Hydrogen

Hello! I was hoping someone could explain, when drawing a Lewis structure, how you know whether an OH/HO is going to be an O attached to the central atom and a hydrogen extending from the oxygen versus when the hydrogen and oxygen are both connected to the central atom. I've heard that OH means an o...
by Abril Guanes 3D
Wed Nov 11, 2020 12:29 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 1E.25
Replies: 1
Views: 36

Re: 1E.25

Hello! The longer and probably the safest way is to write out the electron configuration for all the elements in the group it's asking for. This will probably take time, but it's good practice. When asking for the electron configuration, it's asking for the outermost electrons (including the electro...
by Abril Guanes 3D
Tue Nov 10, 2020 4:51 pm
Forum: Electronegativity
Topic: Sapling #15
Replies: 9
Views: 61

Re: Sapling #15

Hello! I have been to Lavelle's office hours and many UA workshops. All of them have said that Hydrogen boding is possible when the hydrogen is bonded to Nitrogen, Oxygen, or Fluorine. I'm not entirely sure as to why, and hopefully someone can provide that insight, but the general rule of thumb is w...
by Abril Guanes 3D
Tue Nov 10, 2020 4:24 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic v. Covalent Bonding
Replies: 16
Views: 84

Re: Ionic v. Covalent Bonding

I think something else to note is electronegativity. We know the trends for electronegativity looking at the periodic table. Ionic bonds happen between elements that have a very large electronegativity difference (so for example, opposite sides of the periodic table), but covalent bonds happen betwe...
by Abril Guanes 3D
Mon Nov 09, 2020 4:26 pm
Forum: Ionic & Covalent Bonds
Topic: "Favorable"
Replies: 4
Views: 35

Re: "Favorable"

For a bond to be favorable, it means the bond has a very high negative energy (example, today in class with -250 kJ/mol). A very high negative energy means that the bond is releasing a lot of energy, rather than requiring a lot of energy, making it favorable.
by Abril Guanes 3D
Mon Nov 09, 2020 3:57 pm
Forum: Ionic & Covalent Bonds
Topic: Hydrogen Bonds [ENDORSED]
Replies: 9
Views: 52

Re: Hydrogen Bonds [ENDORSED]

Chem_Admin wrote:Lily, I will go through this in my 3pm discussion section today.


I've included an imagine to clear it up!
by Abril Guanes 3D
Mon Nov 09, 2020 3:44 pm
Forum: Ionic & Covalent Bonds
Topic: Hydrogen Bonds [ENDORSED]
Replies: 9
Views: 52

Re: Hydrogen Bonds [ENDORSED]

Can someone please explain what a dipole dipole bond is? We learned dipole moments however I have not heard dipole in any other context until this post. Hello! I am currently in Lavelle's office hours right now. He explained dipole dipole bonds in this manner. Suppose you have two water molecules. ...
by Abril Guanes 3D
Wed Nov 04, 2020 11:09 am
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge and Stability
Replies: 7
Views: 20

Re: Formal Charge and Stability

Generally, Lewis Structures with a formal charge of 0 are more stable than others with a positive or negative charge. Hope this helps!
by Abril Guanes 3D
Wed Nov 04, 2020 11:05 am
Forum: Ionic & Covalent Bonds
Topic: SO4 covalent bond
Replies: 6
Views: 23

Re: SO4 covalent bond

To add to the previous posts, Dr. Lavelle also mentioned a few elements have the ability to have an expanded octet, such as Sulfur, allowing it to have more electrons than the 8 that are inn the octet guideline, so keep an eye out for those when they are mentioned!
by Abril Guanes 3D
Tue Nov 03, 2020 9:45 pm
Forum: Administrative Questions and Class Announcements
Topic: Second Midterm Date
Replies: 9
Views: 68

Re: Second Midterm Date

Week 7 during discussion!
by Abril Guanes 3D
Tue Nov 03, 2020 9:36 pm
Forum: Lewis Structures
Topic: How to find valence electrons of an element
Replies: 6
Views: 33

Re: How to find valence electrons of an element

I found this table that helps visualize it a little bit more clearly. I hope this helps!
by Abril Guanes 3D
Tue Nov 03, 2020 4:29 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Textbook Topic 1E #17
Replies: 1
Views: 20

Re: Textbook Topic 1E #17

Hello! So, Dr. Lavelle touched it briefly, but he explained that for multi-electron atoms AFTER atomic number 20, the 4s state is higher in energy than 3d, meaning the electrons would first fill up the 3d orbital, and then the 4s. So the electron configuration for Mn would be [Ar]3d5 4s2. Because th...
by Abril Guanes 3D
Thu Oct 29, 2020 2:52 pm
Forum: Administrative Questions and Class Announcements
Topic: Participation Points [ENDORSED]
Replies: 62
Views: 892

Re: Participation Points [ENDORSED]

I also keep clicking on my name to view my points but it is not showing. Where do we click again to view our points? Hi! I think it's not directly on your name by right next to your name, on the left there is like a little paper followed by "by (insert name)". I think that means "Pos...
by Abril Guanes 3D
Tue Oct 27, 2020 9:16 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Sapling Homework #8 - Which number do we assign to n(1) versus n(2)
Replies: 4
Views: 41

Re: Sapling Homework #8 - Which number do we assign to n(1) versus n(2)

From my understanding, the n1 and n2 are relatively arbitrary, meaning that yes you change them depending on whether you need a positive or negative answer, so absorption vs emission. I typically use the E= -hR/(n)^2 concept and just do final energy - initial energy. This may also be a way for you t...
by Abril Guanes 3D
Tue Oct 27, 2020 5:32 pm
Forum: Administrative Questions and Class Announcements
Topic: Participation Points [ENDORSED]
Replies: 62
Views: 892

Re: Participation Points [ENDORSED]

Awesome! Thanks :D
by Abril Guanes 3D
Tue Oct 27, 2020 12:25 pm
Forum: Administrative Questions and Class Announcements
Topic: Participation Points [ENDORSED]
Replies: 62
Views: 892

Participation Points [ENDORSED]

Is there any way to check to see if you're getting your participation points through Chemistry Community? I tend to post 5-7 times a week, but I'm not sure if all my posts are "valid" posts to get points and was wondering if there was any way to find out? Thanks!
by Abril Guanes 3D
Mon Oct 26, 2020 6:07 pm
Forum: General Science Questions
Topic: assuming limiting reactant
Replies: 4
Views: 42

Re: assuming limiting reactant

Could you possibly balance the equation and use the mole ratio to see which reactant would theoretically produce less of the product and thus be your limiting reactant? If not, I would assume that yes, the reactant that is given is your limiting.
by Abril Guanes 3D
Mon Oct 26, 2020 3:15 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Writing Out Electron Orbitals
Replies: 2
Views: 31

Re: Writing Out Electron Orbitals

We talked about it briefly, but Lavelle explained it, saying that the interaction between electrons in some elements result inn 3d having less energy that 4s. He says that for multi-electron atoms after atomic number 20, so after Calcium, the 4s state is higher in energy than 3d. I don't know if any...
by Abril Guanes 3D
Mon Oct 26, 2020 3:09 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: In class question
Replies: 1
Views: 41

Re: In class question

So it's a little confusing but I think the 4s1 or 4s2 comes from the need to account for all the electrons. Lavelle explains that for symmetry reasons Cr is more stable with 5 unpaired electrons in 3d state and 1 unpair electron in the 4s state. If you do the electron configuration for Cr: [Ne]3s2 3...
by Abril Guanes 3D
Mon Oct 26, 2020 2:59 pm
Forum: Administrative Questions and Class Announcements
Topic: sapling questions for midterm prep
Replies: 2
Views: 23

Re: sapling questions for midterm prep

Lavelle said that for midterm, up to Question 19 will cover all that is on the midterm
by Abril Guanes 3D
Sat Oct 24, 2020 8:51 am
Forum: Molarity, Solutions, Dilutions
Topic: Problem from Workshop
Replies: 4
Views: 61

Re: Problem from Workshop

For the first question, I'm not sure but it looks like its asking for a 1/5 dilution, meaning the final solution must be 1/5 as concentrated as the original. Since 0.20M is the original concentration, then the final concentration must be 1/5 of that which would be 0.04 M. Then you plug it into this...
by Abril Guanes 3D
Sat Oct 24, 2020 8:51 am
Forum: Molarity, Solutions, Dilutions
Topic: Problem from Workshop
Replies: 4
Views: 61

Re: Problem from Workshop

Hi! Is the 15 you put 15M? Then if so, then yes I'd say it is pretty straightforward since you would be using M1V1=M2V2. You have your initial volume, initial molarity, and final molarity, so just solve for the final volume? For your second question, the c would stand for concentration while M (upp...
by Abril Guanes 3D
Fri Oct 23, 2020 11:25 pm
Forum: Molarity, Solutions, Dilutions
Topic: Problem from Workshop
Replies: 4
Views: 61

Problem from Workshop

I'm going through old worksheets I found on other posts and I came across this question: How many mL of water would you need to add to 40.0 mL of 0.20 M hydrochloric acid to achieve a 1⁄5 dilution? It seems pretty straightforward but I feel like I'm missing something. Can some explain it please? Als...
by Abril Guanes 3D
Fri Oct 23, 2020 7:00 pm
Forum: Photoelectric Effect
Topic: Finding Wavlength
Replies: 3
Views: 28

Re: Finding Wavlength

I don't think you could use those for the same objective. The photoelectric effect is used for finding energy of light, which does not have a rest mass. The de Broglie's, however, is used for electrons and other particles with a rest mass. Therefore, I don't think you would get the same answer, nor ...
by Abril Guanes 3D
Fri Oct 23, 2020 6:46 pm
Forum: Einstein Equation
Topic: Rydberg's Equation
Replies: 9
Views: 52

Re: Rydberg's Equation

Hello! For the most part, it's Final - Initial. I can't think of a situation where we would use Initial - Final. As for the equation, I've heard that you switch N1 and N2, dependent upon whether you're going to get a negative or positive. So, if the problem mentions absorption you would want a posi...
by Abril Guanes 3D
Thu Oct 22, 2020 6:04 pm
Forum: Einstein Equation
Topic: Rydberg's Equation
Replies: 9
Views: 52

Re: Rydberg's Equation

Hello! For the most part, it's Final - Initial. I can't think of a situation where we would use Initial - Final. As for the equation, I've heard that you switch N1 and N2, dependent upon whether you're going to get a negative or positive. So, if the problem mentions absorption you would want a posit...
by Abril Guanes 3D
Wed Oct 21, 2020 8:38 pm
Forum: DeBroglie Equation
Topic: 1B.15 part b and c.
Replies: 3
Views: 43

Re: 1B.15 part b and c.

Hello! I'll break down what I did for each part. A) For part a I used the wavelength = h/p equation. For the top part, h is just Planck's constant and p is momentum so (mass x velocity, which is given). So, it would look something like this wavelength = (6.626x10^-34)/(3.6x10^6)*(9.11x10^-31), which...
by Abril Guanes 3D
Wed Oct 21, 2020 4:21 pm
Forum: Properties of Electrons
Topic: Properties of Electrons and Matter as a Whole
Replies: 5
Views: 33

Re: Properties of Electrons and Matter as a Whole

Hello!
Yes, you are correct in both your thought process. Electrons possess both particle- and wave-like properties. As for the other concept, wavelike properties are only measurable on a really small scale. I believe the cutoff is x10^-15. Anything after that, x10^-16, x10^-17 is not measurable.
by Abril Guanes 3D
Wed Oct 21, 2020 3:32 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Orbitals and Schrodinger's Wave Function
Replies: 2
Views: 22

Orbitals and Schrodinger's Wave Function

During the lecture I got a little confused by the relation between the electron density and the probability of finding an electron. Can someone please explain their relationship? Thanks y'all !
by Abril Guanes 3D
Fri Oct 16, 2020 3:53 pm
Forum: Photoelectric Effect
Topic: photoelectric effect practice problem 1b15
Replies: 2
Views: 43

Re: photoelectric effect practice problem 1b15

Hello! I'll break down what I did for each part. A) For part a I used the wavelength = h/p equation. For the top part, h is just Planck's constant and p is momentum so (mass x velocity, which is given). So, it would look something like this wavelength = (6.626x10^-34)/(3.6x10^6)*(9.11x10^-31), which...
by Abril Guanes 3D
Thu Oct 15, 2020 10:19 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: n1, n2, and emission/absorption
Replies: 2
Views: 52

Re: n1, n2, and emission/absorption

Hi there! I think an easier way of thinking of this is through the concept of Final - Initiation. So if you think as the first part (1/(n1)^2 of the Rydberg equation as the final level and the second part (1/(n2)^2) as the initial, you can now see why this would be emission rather than absorption. I...
by Abril Guanes 3D
Thu Oct 15, 2020 2:30 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty of mass?
Replies: 3
Views: 56

Re: Uncertainty of mass?

Hello! The textbook actually gives one or two problems where it asks for the uncertainty in position and momentum of a baseball and it gives the mass of the baseball, as well as other needed information. You can find these problems on Lavelle's website under the Quantum World practice problems. As K...
by Abril Guanes 3D
Mon Oct 12, 2020 9:52 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg's Constant
Replies: 2
Views: 29

Re: Rydberg's Constant

The second version of the equation is similar to the one you listed below, except that the -R has been distributed so its -R/(n1)^2+R/(n2)^2 so the second half of the equation is positive simply because of the distribution. I think which part is negative is dependent upon what you pull out. So for e...
by Abril Guanes 3D
Mon Oct 12, 2020 4:58 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect Energy and Excess Energy
Replies: 9
Views: 58

Re: Photoelectric Effect Energy and Excess Energy

The amplitude affects the intensity of the light but the experiment revealed that even if you increase the intensity of the light (making more light in essence) it does not eject electors because the energy of the light is not increasing (the light still has the same energy). Thus the experiment rev...
by Abril Guanes 3D
Mon Oct 12, 2020 2:18 pm
Forum: Properties of Light
Topic: Clarification on intensity and amplitude [ENDORSED]
Replies: 6
Views: 54

Re: Clarification on c = (lambda) * V [ENDORSED]

I would say that frequency is dependent more on wavelength, rather than amplitude. Amplitude refers to how high the wave is; however, in the equation amplitude isn't really referred to. Lamda is the distance between peak to peak or trough to trough and that has a relationship with frequency which is...
by Abril Guanes 3D
Tue Oct 06, 2020 7:42 pm
Forum: SI Units, Unit Conversions
Topic: Including the units when solving
Replies: 8
Views: 62

Including the units when solving

I wanted to know if we would be penalized on exams for not putting the units when solving for the answer, but still including the units at the end for the answer? Basically do we have to include units for every single step of the problem or just for the answer?
by Abril Guanes 3D
Tue Oct 06, 2020 7:32 pm
Forum: Molarity, Solutions, Dilutions
Topic: G.19
Replies: 3
Views: 19

Re: G.19

Just to add on, remember to convert the mL to Liters first, since the equation uses liters!
by Abril Guanes 3D
Tue Oct 06, 2020 7:24 pm
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student - Part II [ENDORSED]
Replies: 188
Views: 14331

Re: Advice from a Medical Student - Part II [ENDORSED]

I didn't expect to see a post like this, but it's very refreshing and exciting to see upon the hundreds of threads about chemistry. Thank you for sharing your experience! I wanted to ask about the resources that medical schools (or maybe yours in particular for experience) have to offer for mental h...
by Abril Guanes 3D
Mon Oct 05, 2020 11:02 pm
Forum: Photoelectric Effect
Topic: Electron Mass
Replies: 2
Views: 15

Re: Electron Mass

He mentions this in one of the module videos I think, that the mass of an electron is always constant and will usually be given. You could also check the constants/equations hand out to see if it's listed there. If not, it might be good to memorize it for convenience.

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