Search found 42 matches

by Xinying Wang_3K
Tue Nov 24, 2020 2:45 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Sampling Week 7/8 #6
Replies: 6
Views: 18

Sampling Week 7/8 #6

Can someone explain why SF2 is not linear?
I thought there will be one lone pair above the S atom, and another lone pair below it, making it a linear shape.

Thank you in advance!
by Xinying Wang_3K
Tue Nov 24, 2020 2:42 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Why is CH2Cl2 polar?
Replies: 6
Views: 32

Re: Why is CH2Cl2 polar?

CH2CL2 is polar because the four bonding regions give the molecule a tetrahedral shape, and because of the shape, there must be a dipole moment among the two ends of the molecule, so it is polar.
by Xinying Wang_3K
Tue Nov 24, 2020 2:38 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Sapling Week 7/8 #7
Replies: 4
Views: 22

Re: Sapling Week 7/8 #7

Hi, CH2CL2 makes carbon to form four bonds, so there are 4 electron density regions, which makes the shape tetrahedral. And given the shape is tetrahedral, it is polar and the dipole couldn't be canceled.
by Xinying Wang_3K
Tue Nov 24, 2020 2:35 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Sapling #17, Week 7/8
Replies: 7
Views: 36

Re: Sapling #17, Week 7/8

The 60 degree comes from the triangle that three carbons can form to make one of the possible structures. And resonance structures are not possible in this case. Hope this helps!
by Xinying Wang_3K
Tue Nov 24, 2020 2:33 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Determining Molecular Polarity using VSEPR
Replies: 8
Views: 19

Re: Determining Molecular Polarity using VSEPR

Because as the whole molecule, the two ends are both oxygen atoms, which makes the molecule nonpolar.
by Xinying Wang_3K
Wed Nov 18, 2020 6:57 pm
Forum: Lewis Structures
Topic: When to add double or triple bonds
Replies: 4
Views: 14

Re: When to add double or triple bonds

In some of these cases, the formal charge definite plays a role in deciding the double/triple bond, but when you have a lewis structure that every atom meets the octet rule and the drawing seems symmetrical, you are probably fine cause usually more bonds are added when there are incorrect numbers of...
by Xinying Wang_3K
Wed Nov 18, 2020 6:53 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pair E-
Replies: 37
Views: 130

Re: Lone Pair E-

Hi, yes, lone pair electrons also count in electron density and will affect the shape of the molecules, but they don't count when naming the geometry of the molecule.
by Xinying Wang_3K
Wed Nov 18, 2020 6:51 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: London Dipole
Replies: 3
Views: 23

Re: London Dipole

Hi, London dipole, also called London dispersion force, is an induced dipole, meaning the atom by itself doesn't carry any charges if it has no contact with other atoms/molecules. Dipole-Dipole is permanent, meaning the molecule has a significant difference in electronegativity and it will show a di...
by Xinying Wang_3K
Wed Nov 18, 2020 6:47 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: Hydrogen Bonding
Replies: 5
Views: 17

Re: Hydrogen Bonding

Yes, hypothetically they can for two hydrogen bonds with two different hydrogen atoms.
by Xinying Wang_3K
Wed Nov 18, 2020 6:42 pm
Forum: Administrative Questions and Class Announcements
Topic: 14B Enrollment [ENDORSED]
Replies: 12
Views: 617

Re: 14B Enrollment [ENDORSED]

Thank you, Dr. Lavelle, I was so stressed out when I saw all of your classes are closed.
by Xinying Wang_3K
Wed Nov 18, 2020 6:40 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 3d vs 4s orbitals
Replies: 4
Views: 28

Re: 3d vs 4s orbitals

Hi, yes, 3d will always come before 4s when writing the electron configuration. But 4s has actually slightly lower energy than 3d, so when it comes to losing electrons/adding electrons, there will be a situation like 3d^1 4s^2, since the lower energy level(4s) fills up first. I know it is really con...
by Xinying Wang_3K
Thu Nov 12, 2020 4:49 am
Forum: Dipole Moments
Topic: Sapling #17
Replies: 7
Views: 49

Re: Sapling #17

This question also confused me when I was doing it, and I took multiple attempts. I guess the confusing part is that the question is asking as a whole, not inside of the molecule, so you are trying to find which molecule exhibits overall non-polar characteristics, for example, CH4 will be one of the...
by Xinying Wang_3K
Thu Nov 12, 2020 4:44 am
Forum: Dipole Moments
Topic: induced dipole vs dipole
Replies: 11
Views: 40

Re: induced dipole vs dipole

Dipole-Dipole intermolecular force is stronger than induced-dipole-induced-dipole intermolecular force. The difference in negativities of the two atoms in dipole-dipole is permanent, meaning that the atoms have this difference by itself, whereas in induced-dipole-induced-dipole force the atoms don't...
by Xinying Wang_3K
Thu Nov 12, 2020 4:39 am
Forum: Dipole Moments
Topic: Sapling Week 5-6 HW Question 19
Replies: 4
Views: 17

Re: Sapling Week 5-6 HW Question 19

Hi, I thought it was SO2 when I was solving it. Since S and O has a difference in electronegativity, the force between two molecules would be dipole-dipole, as one end would be more negative than the other.
by Xinying Wang_3K
Wed Nov 11, 2020 5:08 am
Forum: Formal Charge and Oxidation Numbers
Topic: Sampling week 5/6 Q5
Replies: 3
Views: 21

Sampling week 5/6 Q5

For question 5 in the sampling 5/6, can anyone explain what is the correct formal charges for resonance structure A? It has a triple bond between N and O, and O has 1 lone pair of the electron, C has 2 lone pairs. Thank you very much!
by Xinying Wang_3K
Wed Nov 11, 2020 5:01 am
Forum: Resonance Structures
Topic: Sapling HW Weeks 5,6 Question #4
Replies: 2
Views: 28

Re: Sapling HW Weeks 5,6 Question #4

Hi, another resonance structure would be a double bond between C and O(C=O), basically switch the structure given by the question to another O molecule. And the O with 6 lone pairs will have a negative formal charge. Hope this helps.
by Xinying Wang_3K
Thu Nov 05, 2020 5:24 pm
Forum: Ionic & Covalent Bonds
Topic: Sapling HW Week 5/6 #10
Replies: 5
Views: 28

Re: Sapling HW Week 5/6 #10

Hi, as everyone else said, it has to do with the distance on the periodic table, the further on the periodic table, which means it is metal to non-mental, the more ionic the bond is. Hope it helps.
by Xinying Wang_3K
Thu Nov 05, 2020 5:21 pm
Forum: Student Social/Study Group
Topic: Studying Tips
Replies: 23
Views: 86

Re: Studying Tips

Hi, I would say first understand all the major concepts/formulas and then practice with the textbook questions and sapling. For me, doing practice problems is really helpful, and that also further deepens your understanding of the materials. Hope it helps.
by Xinying Wang_3K
Thu Nov 05, 2020 5:16 pm
Forum: Lewis Structures
Topic: Sapling Week5/6 Q3
Replies: 5
Views: 35

Sapling Week5/6 Q3

Can someone explain how to start on this? what is the molecular formula of these molecules and would formal charges be different? Here is the question: The formulas of the bromate ion, BrO−3, and chlorate ion, ClO−3, are very similar. However, the formulas of the nitrate ion and phosphate ion contai...
by Xinying Wang_3K
Thu Nov 05, 2020 5:12 pm
Forum: Lewis Structures
Topic: Sapling Lewis Strucutres
Replies: 5
Views: 45

Re: Sapling Lewis Strucutres

My interpretation of the wording is "which lewis structure is most likely to happen/appear to this molecule", in order words, it is asking which one of the lewis structures is the most stable one. Hope this helps.
by Xinying Wang_3K
Thu Nov 05, 2020 5:09 pm
Forum: Resonance Structures
Topic: Delocalized Electrons
Replies: 5
Views: 24

Re: Delocalized Electrons

I am also confused on the same concept, I guess it's just hard to visualize what happened to those delocalized electrons while switching between double and single bonds.
by Xinying Wang_3K
Fri Oct 30, 2020 3:46 am
Forum: Trends in The Periodic Table
Topic: Sapling Hw 2, 3, 4 Question 20
Replies: 4
Views: 40

Re: Sapling Hw 2, 3, 4 Question 20

I also had the same question, and this is really helpful! Thank you.
by Xinying Wang_3K
Fri Oct 30, 2020 3:43 am
Forum: Quantum Numbers and The H-Atom
Topic: Sampling week 2,3,4, Q8
Replies: 3
Views: 28

Sampling week 2,3,4, Q8

Given the wavelength and ask to find the initial energy level and ending energy level, after using v=R(1/(n2)^2-1/(n1)^2), then I have (1/(n2)^2-1/(n1)^2)=some number, how do you find n1 and n2 from fractions or decimals?
by Xinying Wang_3K
Fri Oct 30, 2020 3:38 am
Forum: Quantum Numbers and The H-Atom
Topic: Rydberg equation
Replies: 7
Views: 29

Rydberg equation

In the equation: v=R(1/(n2)^-1/(n1)^2), is n1 the higher one, or is n2 the higher one? I always got confused about these two.

Thanks in advance!
by Xinying Wang_3K
Fri Oct 30, 2020 3:34 am
Forum: Photoelectric Effect
Topic: Sampling week 2,3,4, Q9
Replies: 2
Views: 31

Sampling week 2,3,4, Q9

For question 9 in the sampling homework for week 2,3,4, I got the wavelength, but I don't know how to test if the photoelectric effect is the cause of sparking or not.

Can someone explain the second part of question 9 please?

Thanks in advance!
by Xinying Wang_3K
Fri Oct 30, 2020 3:27 am
Forum: Photoelectric Effect
Topic: Sampling HW Q4
Replies: 5
Views: 42

Sampling HW Q4

For Q4 in the homework, I understand I need to find E through E=hv, but how I proceed from there? I am quite confused about how to find the work function.

Thanks in advance!
by Xinying Wang_3K
Thu Oct 22, 2020 5:09 am
Forum: *Shrodinger Equation
Topic: Nodal Planes
Replies: 3
Views: 45

Re: Nodal Planes

I had exactly the same question, and you worded it really clear. Thanks.
by Xinying Wang_3K
Thu Oct 22, 2020 5:03 am
Forum: *Shrodinger Equation
Topic: Schrodinger's Equation
Replies: 5
Views: 82

Re: Schrodinger's Equation

I am also very confused about the equation Hψ=Eψ, especially what each of the variables stands for and what scenario should we use it. However, it seems Dr. Lavelle mentioned this majorly for introducing the idea of atomic orbitals. So I am not sure to what extent should we understand this equation ...
by Xinying Wang_3K
Tue Oct 20, 2020 11:47 pm
Forum: Student Social/Study Group
Topic: How are you studying?
Replies: 196
Views: 827

Re: How are you studying?

I do believe the studying method varies from person to person, especially for chem. For me, I listen to lectures and practice on homework, there are definitely times that I have no clue how to start solving a question, then I will go to textbooks or chemistry community, sometimes you can find a simi...
by Xinying Wang_3K
Tue Oct 20, 2020 11:43 pm
Forum: Properties of Light
Topic: Planck's Constant
Replies: 7
Views: 48

Re: Planck's Constant

Yes, Planck's constant is 6.626 x 10^-34 J/s, and there is no need to memorize it as there are a lot of constants in this chapter, during the quiz/test, the value should be given.
by Xinying Wang_3K
Mon Oct 19, 2020 4:44 am
Forum: Properties of Light
Topic: Difference between E=hv and E=hc/v?
Replies: 9
Views: 59

Difference between E=hv and E=hc/v?

Hi,
I was working on the Sapling homework, and I got confused between the formula E=hv and E=hc/v. I am wondering what is the difference between these two formulas and when to use which?

Thanks in advance!
by Xinying Wang_3K
Thu Oct 15, 2020 1:24 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Sapling Week 2 & 3 HW Problem 5
Replies: 7
Views: 91

Re: Sapling Week 2 & 3 HW Problem 5

I understand, the question was worded quite confusingly, but once you know what it's asking it's not that hard. Number of spectral lines would be equal to the number of times the electron emits energy, and the electron would do that for each complete energy level it moves down since energy is quant...
by Xinying Wang_3K
Thu Oct 15, 2020 1:15 am
Forum: Student Social/Study Group
Topic: iPad vs Paper notes
Replies: 32
Views: 199

Re: iPad vs Paper notes

Hi, for me it really depends on the requirement of the class. I am using the IPad for my math class, since it requires me to upload a pdf version of my homework on website, and I am not a big fan of using a scanner every time for my homework. Instead, apps like GoodNotes and notability are really us...
by Xinying Wang_3K
Thu Oct 15, 2020 1:10 am
Forum: Properties of Light
Topic: work function
Replies: 15
Views: 138

Re: work function

Yeah, I think a scientific calculator is definitely necessary for problems like this, and just remember to pay extra attention to negatives, decimal places, etc, when plugging in the numbers.
by Xinying Wang_3K
Thu Oct 15, 2020 1:07 am
Forum: Properties of Electrons
Topic: Lyman vs. Balmer series
Replies: 20
Views: 146

Re: Lyman vs. Balmer series

When electron drops to n=1, it emits UV light, so it is the Lyman series. When electron drops to n=2, it emits visible light, so it is the Balmer series.
by Xinying Wang_3K
Thu Oct 15, 2020 1:04 am
Forum: Photoelectric Effect
Topic: 10/14 Lecture Threshold Energy
Replies: 8
Views: 66

Re: 10/14 Lecture Threshold Energy

Usually the threshold energy, which is the same as work function, will be given to you in the question. The value of the threshold energy is not a fixed constant, and it varies for different metals. Hope this is somewhat helpful.
by Xinying Wang_3K
Tue Oct 06, 2020 8:04 pm
Forum: Empirical & Molecular Formulas
Topic: Sapling Question #9 find mass of carbon
Replies: 3
Views: 51

Sapling Question #9 find mass of carbon

Given that there is 2.275g CO2, how to find the mass of C?

I got stuck after 2.275g divide by 44g/mol=0.0517mol of CO2, do I need to use the percentage of composition for C?

Thank you!
by Xinying Wang_3K
Tue Oct 06, 2020 7:54 pm
Forum: Limiting Reactant Calculations
Topic: Sapling Question #10
Replies: 9
Views: 123

Sapling Question #10

Hi, I know there are a lot of topics about #10 already, but I still don't know how to find the moles of 3-methyl-3-hexanone. I understand the mass of 2-butanone can be calculated using 0.40mL and 0.81g/mL, and the number of mole of 2-butanone can be calculated by dividing 72.1g/mol, but how to find ...
by Xinying Wang_3K
Mon Oct 05, 2020 7:58 am
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student [ENDORSED]
Replies: 221
Views: 116080

Re: Advice from a Medical Student [ENDORSED]

Thank you for your advice! it really makes things clear for me.
by Xinying Wang_3K
Mon Oct 05, 2020 7:52 am
Forum: Significant Figures
Topic: Significant Figures In A Given Weight
Replies: 11
Views: 172

Re: Significant Figures In A Given Weight

Hi! I think "7" has one sig fig, and if the 7 gram is used in the calculation, it does limit the sig fig to one.

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