## Search found 98 matches

Wed Jan 20, 2021 2:34 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook 6D.7
Replies: 3
Views: 16

### Re: Textbook 6D.7

Thanks, that helped a lot. I realized it was just a calculation error.
Wed Jan 20, 2021 2:33 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook 6D.3 a)
Replies: 2
Views: 10

### Textbook 6D.3 a)

For problem 6D.3 a), I solved for [H+] by 10^-1.2 = .063. Then I set ka = (.063)^2 / (.1-.063). I keep getting .108 instead of .09 like the answer key has. Can someone tell me where I went wrong?
Mon Jan 18, 2021 2:41 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook 6D.7
Replies: 3
Views: 16

### Textbook 6D.7

Could someone help me solve parts a and b of 6D.7? For a, I set 3.0 x 10^-8 = (2.512 x 10^-5)^2 / x - 2.512 x 10^-5 and solved for x to get the original concentration of HClO. I keep getting 2.51 x 10^-5 for X instead of .021. for b, I set 1.7 x 10^-6 = (1.58 x 10^-4)^2 / (x - 1.58 x 10^-4) and solv...
Mon Jan 18, 2021 2:36 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6D.15
Replies: 2
Views: 19

### Re: 6D.15

To solve a), divide 10^-14 by the pKb of NH3 to get the pKa of NH4. Then set the pKa (5.56 x10^-10) = (x^2)/(.19-x) and you should get the right answer.
Sun Jan 17, 2021 8:00 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm 1
Replies: 4
Views: 22

### Midterm 1

Does anyone know what day midterm 1 is scheduled for?
Sun Jan 17, 2021 1:30 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling 9 and 10
Replies: 1
Views: 34

### Sapling 9 and 10

Can someone explain the reasoning behind sapling 9 and 10 for the hw due at the end of week 3? I saw the two tables showing that when pH > pKa an acid deprotonates, and when pH < pka a base protonates, etc., but I forgot why that happens.
Fri Jan 15, 2021 2:04 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook problem 5I.25
Replies: 1
Views: 28

### Textbook problem 5I.25

Is anyone else having problems with 5I.25? I couldn't get the equilibrium concentrations given in the answer key, so I plugged them (the answers) into the K expression and I got 82.0 for the equilibrium constant. This doesn't match the equilibrium constant given in the problem (85), so I'm wondering...
Fri Jan 15, 2021 1:27 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ka and Kb equation
Replies: 3
Views: 20

### Ka and Kb equation

When we talk about the equation Ka x Kb = Kw, do the Ka and Kb refer to the equilibrium constants for an acid base pair? For example, if we're talking about CH3COOH, the Ka refers to the equilibrium constant for CH3COOH, but the Kb refers to the equilibrium constant for CH3COO-? Or, if we're talking...
Thu Jan 14, 2021 10:43 pm
Forum: Ideal Gases
Topic: Question 4 Sapling [ENDORSED]
Replies: 8
Views: 119

### Re: Question 4 Sapling[ENDORSED]

I didn't use 1/Kp for this problem, you shouldn't have to unless for some reason you need to put the products on the bottom of your Kp expression. If it helps, you should be getting 0.00985 bar for x, which you would then use to add up the partial pressures. Maybe you could post your work or what yo...
Thu Jan 14, 2021 10:02 pm
Forum: Administrative Questions and Class Announcements
Topic: More Audio Visual Focus Topics
Replies: 8
Views: 22

### Re: More Audio Visual Focus Topics

From what I know from 14a, Dr. Lavelle posts audio visual focus topics for the first sections only.
Tue Jan 12, 2021 12:18 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook Table 5G.2
Replies: 3
Views: 33

### Textbook Table 5G.2

Many of the textbook problems in Focus 5 refer to table 5G.2, which is a table of the equilibrium constants for different reactions at different temperatures. There is both a K column and a Kc column, and sometimes those values are the same for a reaction and sometimes they're different. Can someone...
Tue Jan 12, 2021 12:15 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Unchanged K, Changed Pressure
Replies: 2
Views: 22

### Re: Unchanged K, Changed Pressure

I'm not sure I fully understand your question, but basically, decreasing the pressure changes the concentrations of the reactants and products because concentration is measured in mol/L. If the moles of the reactants and products stay the same but the volume of the container changes, the concentrati...
Mon Jan 11, 2021 11:34 am
Forum: Student Social/Study Group
Topic: Study Tips
Replies: 30
Views: 75

### Re: Study Tips

I also do all of the practice problems from the textbook, and I usually make a study guide right before each midterm/final that summarizes all of the main information I need to know. I find that this really helps because I have to actively review each concept while making the study guide, and then I...
Mon Jan 11, 2021 11:30 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook 5I.3
Replies: 3
Views: 13

### Textbook 5I.3

5I.3 In a gas-phase equilibrium mixture of H2, I2, and HI at 500. K, (HI)=2.21×10^−3 mol⋅L−1 and [I2]=1.46×10^−3 mol⋅L−1. Given the value of the equilibrium constant in Table 5G.2, calculate the equilibrium molar concentration of H2. I keep getting 4.21 x 10^-6 mol/L for the concentration of H2 inst...
Thu Jan 07, 2021 12:09 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K for gases
Replies: 4
Views: 26

### Re: K for gases

Yes, you should format the K for gases as P_species. The book explains it like this: A Note on Good Practice: In some cases you will see an equilibrium constant denoted Kp to remind you that it is expressed in terms of partial pressures. However, the subscript P is unnecessary because, by definition...
Thu Jan 07, 2021 12:03 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Difference between "sits" and "shifts"
Replies: 5
Views: 54

### Re: Difference between "sits" and "shifts"

I definitely agree with the posts above. I think it's also helpful to think of "sits" as something static, such as the equilibrium constant K which never changes. "Shifts", on the other hand, has to do with changes in concentration or partial pressure. You can associate this word...
Wed Jan 06, 2021 11:58 pm
Forum: Ideal Gases
Replies: 179
Views: 106766

The textbook is very confusing for me; I find it difficult to process any information. Any tips? good alternatives? If you have problems reading the textbook straight through, maybe try just relying on lecture information. If you can get all of the textbook practice problems right without reading t...
Wed Jan 06, 2021 11:54 pm
Forum: Ideal Gases
Replies: 179
Views: 106766

Are there a lot of topics in the book that are not covered during lecture that show up on tests? In my experience from 14A, the topics that are in the book but not in lecture are not usually on the tests. The best way to make sure you know everything for the test is to go to Dr. Lavelle's website a...
Tue Jan 05, 2021 11:36 pm
Forum: Administrative Questions and Class Announcements
Topic: posting screenshots
Replies: 2
Views: 34

### Re: posting screenshots

Sun Dec 13, 2020 10:38 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Textbook 2E.25
Replies: 3
Views: 14

### Re: Textbook 2E.25

Hm that's weird bc I screenshotted that from the soln manual. Maybe it's bc I was on the bookshelf app?
Sun Dec 13, 2020 3:53 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Textbook 2E.25
Replies: 3
Views: 14

### Textbook 2E.25

solution.png (10.4 KiB) Viewed 14 times

I'm not sure why a and b are polar and c and d are nonpolar. Seems like because of symmetry b and c should be nonpolar and a and d should be polar
Sat Dec 12, 2020 10:31 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordination Compounds and Ionic Bonds
Replies: 2
Views: 22

### Coordination Compounds and Ionic Bonds

Since forming a coordination compound involves a ligand donating a pair of electrons to a metal cation, would the bond between a ligand and the metal be considered an ionic bond? Also, how would this relate to Cl- as a ligand for Na. In this case isn't the Cl donating an electron to the Na? How woul...
Sat Dec 12, 2020 9:20 pm
Forum: Bond Lengths & Energies
Topic: hydrogen bonding vs ion-dipole
Replies: 5
Views: 54

### Re: hydrogen bonding vs ion-dipole

Hydrogen bonding can only occur between an H that is already bonded to a N, O, or F, and an N, O, or F. I think ions attract H+s too strongly, so if a Hydrogen was attracted to an anion it would probably go through an acid base reaction instead of just forming a hydrogen bond. The second part is jus...
Sat Dec 12, 2020 9:15 pm
Forum: Properties & Structures of Inorganic & Organic Bases
Topic: Strong Bases
Replies: 1
Views: 21

### Strong Bases

Does anyone know why all of the alkaline earth metals form metal hydroxides that are strong bases except Be and Mg? It seems to me that since they're in the same group they would also form strong bases

Sat Dec 12, 2020 7:49 pm
Forum: Bond Lengths & Energies
Topic: hydrogen bonding vs ion-dipole
Replies: 5
Views: 54

### hydrogen bonding vs ion-dipole

Are hydrogen bonds or ion-dipole bonds stronger? From the notes it seems like hydrogen bonding releases more energy than ion-dipole (-20 vs -15), but from what I've seen online it looks like ion-dipole forces are stronger than hydrogen bonds.
Sat Dec 12, 2020 2:31 am
Forum: Lewis Acids & Bases
Topic: Aluminum Chloride naming in today's review
Replies: 4
Views: 37

### Re: Aluminum Chloride naming in today's review

From what I've seen online Aluminium chloride is actually polar covalent because of the high polarizing power of Al3+. However, I think because Al always has an oxidation state of 3+, it's implied that there are 3 chlorines.
Fri Dec 11, 2020 4:24 pm
Forum: Lewis Acids & Bases
Topic: Aluminum Chloride naming in today's review
Replies: 4
Views: 37

### Aluminum Chloride naming in today's review

Since Aluminum Chloride is a molecular compound, why wouldn't we name it Aluminum trichloride as following the naming rules for molecular compounds? Can all molecular compounds be named without the prefixes for each element?
Fri Dec 11, 2020 4:04 pm
Forum: Naming
Topic: tetraamminedichloronickel (II) example from review
Replies: 3
Views: 57

### tetraamminedichloronickel (II) example from review

In today's review Dr. Lavelle talked about the difference between cis and trans coordination compounds. I understand the examples he gave, but I wanted to confirm that if the two Cl's are next to each other but in different planes, is the compound still named cis- tetraamminedichloronickel (II)? On ...
Fri Dec 11, 2020 3:45 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Chelating Ligands vs Polydentate ligands
Replies: 5
Views: 30

### Chelating Ligands vs Polydentate ligands

What's the difference between chelating ligands and polydentate ligands? Are these just two words for the same thing?
Sat Dec 05, 2020 7:42 pm
Forum: Bronsted Acids & Bases
Topic: Relative strength of acids and bases
Replies: 2
Views: 23

### Re: Relative strength of acids and bases

A- stands for the acid once it has lost its hydrogen, H+ stands for hydrogen, and AH stands for the original formula of the acid. The chemical equation looks like this: AH → A- + H+ The brackets [] indicate concentration (for example, [H+] is concentration of hydrogen). To solve for the Ka, you need...
Sat Dec 05, 2020 7:38 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Pka and Ka
Replies: 6
Views: 51

### Re: Pka and Ka

The Ka value is the acid dissociation constant, or the extent to which a weak acid dissociates in solution. Higher Ka means a stronger acid. You get the pKa by taking the -log of the Ka (-logka = pKa). The pKa also tells you how strong the acid is, in an easier to look at way. The lower the pKa, the...
Sat Dec 05, 2020 12:58 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Pulling the proton
Replies: 3
Views: 34

### Re: Pulling the proton

Dissociation is directly related to the strengths of bonds and the stability of the resulting anions. I think here you're talking about R - COOH, carboxylic acid. Carboxylic acid is a weak acid, meaning it only dissociates partially in water (some of the molecules dissociate, some do not). The disso...
Sat Dec 05, 2020 12:45 am
Forum: Naming
Topic: Amphoteric Compund
Replies: 5
Views: 38

### Re: Amphoteric Compund

Amphoteric compounds act as either bases or acids depending on what other compound they're mixed with. H2O is the most common example. When in solution with HCl, an acid, it acts as a base and accepts the H+ from the HCl. When in solution with an acid such as NaOH, it acts as an acid and gives off a...
Sat Dec 05, 2020 12:41 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: ligand names
Replies: 10
Views: 65

### Re: ligand names

I don't think so, I could be wrong though.
Fri Dec 04, 2020 2:06 am
Forum: Student Social/Study Group
Topic: How are you?
Replies: 111
Views: 754

### Re: How are you?

I'm doing okay! I kinda feel like I'm falling behind on chem so I'll prob do a lot of reading and practice problems over the weekend, but other that, not bad.
Wed Dec 02, 2020 2:15 am
Forum: Student Social/Study Group
Topic: How have your study habits changed?
Replies: 45
Views: 309

### Re: How have your study habits changed?

From the last midterm to this most recent one, I've stopped taking detailed textbook notes since I feel like those didn't help too much. Instead I focused on doing the practice problems in the textbook multiple times to make sure I thoroughly understood them.
Tue Nov 24, 2020 10:55 pm
Forum: Administrative Questions and Class Announcements
Topic: Chem 14B
Replies: 9
Views: 91

### Re: Chem 14B

For anyone in a later lecture time, are recorded lectures usually released for everyone at the earliest lecture time? (for example, the first lecture this quarter is at 10, can you access the recorded lecture at 10 even if your class technically starts at 12?)
Tue Nov 24, 2020 7:11 pm
Forum: Hybridization
Topic: Sp3d or dsp3
Replies: 22
Views: 863

### Re: Sp3d or dsp3

I think Dr. Lavelle put it as dsp3 in the notes because that's how the textbook puts it, but standard convention is sp3d
Tue Nov 24, 2020 6:45 pm
Forum: Hybridization
Topic: Finding Hybridization
Replies: 6
Views: 28

### Re: Finding Hybridization

The number of lone pairs and bonds together are called regions of electron density and determine the hybridization. For example, if C had 1 single bond, 1 double bond and 1 lone pair, it would have 3 total regions of electron density and sp^2 hybridization. As far as I know, there are no exceptions.
Mon Nov 23, 2020 7:28 pm
Forum: Sigma & Pi Bonds
Topic: Resonance and pi bonds
Replies: 3
Views: 47

### Re: Resonance and pi bonds

Dr. Lavelle talked about molecular orbitals today during the lecture when he was talking about benzene, but he said that's beyond the scope of our course and not to worry too much about it. From the picture in the lecture though, it seems like the 2p orbitals for all of the carbons in benzene were i...
Mon Nov 23, 2020 7:17 pm
Forum: Student Social/Study Group
Replies: 86
Views: 866

### Re: Big Sad: Midterm 2

I definitely did worse on this one too, but I'm gonna try to stay positive until I get my score back. I also heard that there's a chance of extra credit at the end of the quarter, don't take my word for that though.
Mon Nov 23, 2020 3:20 pm
Forum: Sigma & Pi Bonds
Topic: sp3d orbitals
Replies: 4
Views: 61

### Re: sp3d orbitals

It looks similar to an sp3 or sp2 orbital. I've attached a chart of what many of the hybridized orbitals look like below.

Sat Nov 21, 2020 9:21 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: sapling 6
Replies: 3
Views: 44

### sapling 6

Here is sapling's explanation for why XeF2 is a linear molecule XeF2.png I thought Dr. Lavelle said in lecture that lone pair electrons would occupy the axial positions first, in order to ensure that the lone pairs are as far away from each other as they can be. From this, I assumed that if there ar...
Wed Nov 18, 2020 3:07 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electrostatic potential equation
Replies: 2
Views: 46

### Electrostatic potential equation

Can someone explain how exactly the electrostatic potential equation is related to shielding? Do the charges that are used in the equation potential energy = (q1)(q2)/r refer to the charge of two electrons or the charge of an electron and the nucleus? Does a higher value for electrostatic potential ...
Wed Nov 18, 2020 2:55 am
Forum: Quantum Numbers and The H-Atom
Topic: Outline 2 - properties of electrons
Replies: 2
Views: 59

### Outline 2 - properties of electrons

Dr. Lavelle's Outline 2 asks us to Name and explain the relationship of each of the four s-, p-, and d-orbitals to the properties of electrons in these states. All I can think of to answer this is that electrons in the s subshell penetrate the nucleus and therefore have more shielding power. Likewis...
Wed Nov 18, 2020 1:13 am
Forum: Electronegativity
Topic: Periodic Table Trends
Replies: 9
Views: 82

### Re: Periodic Table Trends

James Patanian 2C wrote:Another thing is when drawing the structure of a compound, the most electronegative atom(s) (or highest ionization energy) is the one in the middle of the other atoms.

I thought the atom with the lowest ionization energy/lowest electronegativity goes in the middle
Wed Nov 18, 2020 12:59 am
Forum: Lewis Structures
Topic: Textbook Problem 2C.3
Replies: 3
Views: 49

### Textbook Problem 2C.3

Why is the H bonded to an O atom and not the central Cl atom in this Lewis structure?

Tue Nov 17, 2020 10:30 pm
Forum: Administrative Questions and Class Announcements
Topic: Chem14B Waitlist Spots
Replies: 6
Views: 90

### Re: Chem14B Waitlist Spots

^regarding my previous post. All the last spots open are for a 6pm discussion session, which I'd rather not do but will take over no class at all. Should I just enroll in that to be safe?

Edit: nvm LOL it filled up
Tue Nov 17, 2020 10:27 pm
Forum: Administrative Questions and Class Announcements
Topic: Chem14B Waitlist Spots
Replies: 6
Views: 90

### Re: Chem14B Waitlist Spots

I was planning to sign up for chem 14b during 2nd pass too but changed my mind just now because I saw spots were filling up. I had to take a waitlisted spot to get the discussion time I need, can anyone confirm that people on the waitlist get in? Also Nane at first I was thinking if I didn't get 14b...
Mon Nov 16, 2020 6:21 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Ni electron configuration and Textbook Problem 2A.9
Replies: 1
Views: 20

### Ni electron configuration and Textbook Problem 2A.9

The electron configuration for Ni is [Ar] 3d⁸4s². Since having a full 3d subshell usually results in lower energy, why isn't the electron configuration [Ar] 3d^10? This is especially confusing for me considering the electron configuration for Cu+ is [Ar] 3d^10. On a related note, here's textbook pro...
Mon Nov 16, 2020 5:38 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Textbook Problem 1E.5
Replies: 3
Views: 34

### Re: Textbook Problem 1E.5

I was looking through the notes again and I think when the question talks about penetrating the nucleus, it's referring to the nodal planes of the atomic orbitals. Both p and d orbitals have at least one nodal plane (area with zero probability of electron density) running through the nucleus. S orbi...
Mon Nov 16, 2020 5:33 pm
Forum: Dipole Moments
Topic: Dipole representation on midterm 2
Replies: 9
Views: 113

### Dipole representation on midterm 2

In the textbook two representations of dipoles were shown, and I've attached that image below. Which one will be used on the midterm?

Mon Nov 16, 2020 5:29 pm
Forum: Dipole Moments
Topic: Net Dipole Moments
Replies: 4
Views: 32

### Re: Net Dipole Moments

I would go with your second answer. There are dipoles in between each F atom and the S atom, but because the molecule is symmetrical they cancel out and there is no net dipole moment. In other words, the molecule as a whole is nonpolar.
Mon Nov 16, 2020 12:22 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Textbook Problem 1E.5
Replies: 3
Views: 34

### Textbook Problem 1E.5

1E.5 Which of the following statements are true for many-electron atoms? If false, explain why. (a) The effective nuclear charge Zeff e- is independent of the number of electrons present in an atom. (b) Electrons in an s-orbital are more effective than those in other orbitals at shielding other elec...
Thu Nov 12, 2020 11:29 pm
Forum: Dipole Moments
Topic: Sapling #19 [ENDORSED]
Replies: 1
Views: 63

### Sapling #19[ENDORSED]

Did anyone else notice that one of the molecules on #19 for sapling appears to be SO2 but is referred to as H2S in the solution manual?
Thu Nov 12, 2020 11:19 pm
Forum: Resonance Structures
Topic: Resonance structures contribution to overall structure
Replies: 4
Views: 17

### Re: Resonance structures contribution to overall structure

I think the best way to do this is to look at formal charge. The resonance structure with the least extreme values for formal charge should be the most common one. You could also look at experimental data and compare the experimental bond lengths to the theoretical lengths of single and double bonds...
Thu Nov 12, 2020 11:17 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Sapling Weeks 5-6 #9
Replies: 3
Views: 63

### Re: Sapling Weeks 5-6 #9

You pretty much just have to memorize the rules for oxidation numbers. Oxygen always has an oxidation number of -2, except in peroxides and F2O. If you add up the -2 charges of all 4 oxygens, you get -8. In order for the charge of the overall molecule to be -1, Cl must have an oxidation number of +7...
Thu Nov 12, 2020 11:06 pm
Forum: Lewis Structures
Topic: Aqueous v Solid
Replies: 8
Views: 63

### Re: Aqueous v Solid

A good way to remember this is that the root aqua of aqueous means water in Latin. Therefore, aqueous refers to a solute dissolved in water. When physically looking at aqueous solutions, they look like a liquid, not a solid.
Thu Nov 12, 2020 11:02 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: Polar molecules and Dipole-Induced Dipole Interactions
Replies: 2
Views: 18

### Re: Polar molecules and Dipole-Induced Dipole Interactions

I'm pretty sure that would just be called a dipole-dipole interaction, because both molecules are already polar and already have dipoles. I'm sure that as the molecules interact with each other, there are some induced dipole forces happening as electrons are constantly moving. However, dipole-dipole...
Thu Nov 12, 2020 10:57 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: Dispersion & Size
Replies: 1
Views: 14

### Re: Dispersion & Size

It's important to think about polarizability here. Increasing the size of an anion increases its polarizability because the electrons are spread out over a larger area and aren't as strongly attracted to the nucleus of the anion. The potential energy equation Ep determines how strong the london disp...
Sun Nov 08, 2020 1:58 am
Forum: Trends in The Periodic Table
Topic: Effective Nuclear Charge
Replies: 3
Views: 26

### Re: Effective Nuclear Charge

Effective nuclear charge can be found using the equation (effective nuclear charge) = (number of protons) - (shielding constant), or Zeff = Z-S. It basically refers to how strongly attracted an electron is to the nucleus. The higher the n value for an electron, the further it is away from the nucleu...
Sun Nov 08, 2020 1:50 am
Forum: Formal Charge and Oxidation Numbers
Topic: Calculating Formal Charge
Replies: 9
Views: 98

### Re: Calculating Formal Charge

What you are describing is how we determine the charge of a polyatomic ion (a molecule with an overall charge). I don't think this is generally referred to as finding the formal charge of the molecule, it's just called finding the charge of the polyatomic ion.
Sun Nov 08, 2020 1:47 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Replies: 1
Views: 20

As far as I know, he has not gone over Bohr radius yet.
Thu Nov 05, 2020 1:09 am
Forum: Lewis Structures
Topic: Formal Charge and Lewis Strucutre
Replies: 3
Views: 27

### Re: Formal Charge and Lewis Strucutre

I don't think there's a faster way, but I think the more you practice the faster you'll be. Another way to think about the equation is instead of saying FC = Valence electrons - (lone electrons + bonded electrons/2), you can just think of it as FC = Valence electrons - (lone electrons + number of bo...
Wed Nov 04, 2020 12:02 am
Forum: Student Social/Study Group
Topic: How many points for an A and above?
Replies: 10
Views: 139

### Re: How many points for an A and above?

I would assume an A is the standard 90%, which is 450 points. If you're asking about a 4.0 (A and A+), that's usually cut off at 93% or 465 points.
Tue Nov 03, 2020 11:59 pm
Forum: Lewis Structures
Topic: Where does the formal charge go?
Replies: 4
Views: 31

### Re: Where does the formal charge go?

If you click more at the top of the box on sapling, you should be able to select a plus sign or a negative sign. Click on that and then click on the atom you want to assign a formal charge to. The plus and negative signs are right next to the lone pairs of electrons and single electrons, if that hel...
Wed Oct 28, 2020 12:03 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic vs Molecular Spectroscopy (Outline 2)
Replies: 3
Views: 54

### Re: Atomic vs Molecular Spectroscopy (Outline 2)

I asked my TA, and basically the difference is that in molecular spectroscopy the electrons don't belong to a single atomic orbital. Instead, the shape of the molecular orbital is a combination of the standard s, p, d, and f orbitals that you see in atomic spectroscopy. Also, one orbital oftentimes ...
Tue Oct 27, 2020 6:20 pm
Forum: DeBroglie Equation
Topic: Textbook Problem 1B.21
Replies: 2
Views: 28

### Re: Textbook Problem 1B.21

Thanks! I realized I just made a calculation error when converting mph to m/s
Tue Oct 27, 2020 3:49 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Textbook Problem 1B.27
Replies: 1
Views: 49

### Textbook Problem 1B.27

1B.27 A bowling ball of mass 8.00 kg is rolled down a bowling alley lane at 5.00±5.0 m⋅s−1. What is the minimum uncertainty in its position? I tried solving this equation by plugging in delta x = h/4(pi)(8.00 kg)(10 m.s^-1). However, I keep on getting delta x = 6.6x10^-37 m instead of the textbook a...
Tue Oct 27, 2020 3:44 pm
Forum: DeBroglie Equation
Topic: Textbook Problem 1B.21
Replies: 2
Views: 28

### Textbook Problem 1B.21

1B.21 A baseball must weigh between 5.00 and 5.25 ounces (1 ounce = 28.3 g). What is the wavelength of a 5.15-ounce baseball thrown at 92 mph? I tried solving this textbook problem by converting 5.15 oz to kg, converting 92 mph to m/s, and then plugging my values into the de Broglie equation lambda)...
Tue Oct 27, 2020 3:40 pm
Forum: DeBroglie Equation
Topic: When to Use DeBroglie Equation vs E=hv Equation
Replies: 5
Views: 70

### Re: When to Use DeBroglie Equation vs E=hv Equation

Just to clarify, the de Broglie equation can be used for photons. In fact, de Broglie derived it using E = hv and c = (lambda)(v). However, in order to find the energy using the de Broglie equation we would need to know the momentum of the photon, which we're not usually given. (We would not be able...
Tue Oct 27, 2020 3:30 pm
Forum: Properties of Light
Topic: Energy Equations Confusion
Replies: 6
Views: 51

### Re: Energy Equations Confusion

Minh, the kinetic energy is already given and you wouldn't want to use the de Broglie equation here because you aren't given the momentum of the incident light, and you are trying to solve for the wavelength of the incident light not the wavelength of the ejected electron. I believe I saw this probl...
Tue Oct 27, 2020 3:27 pm
Forum: Properties of Light
Topic: Energy Equations Confusion
Replies: 6
Views: 51

### Re: Energy Equations Confusion

In order to solve this you need to know the work function of the substance the incident light is ejecting the electron from. Once you know this you can use the photoelectric equation (kinetic energy of electron) = (energy of photon) - (work function). Plug in the kinetic energy of the electron and t...
Tue Oct 27, 2020 3:21 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: The Quantum World Outline
Replies: 3
Views: 67

### The Quantum World Outline

One of the bullet points on the outline Dr. Lavelle gave was With respect to electron transitions that give rise to a UV or visible spectrum: understand the difference between electronic transitions in atomic orbitals (atomic spectroscopy) and electronic transitions in molecular orbitals (molecular ...
Tue Oct 27, 2020 12:30 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Spectral lines/hydrogen emission spectrum
Replies: 4
Views: 64

### Spectral lines/hydrogen emission spectrum

Hi everyone, I'm a bit confused on what spectral lines are. I get that they represent the energy/frequency/wavelength of a photon that is given off during an electron transition from a higher to a lower energy level, but I don't understand why they're drawn as lines. On a related note, why does hydr...
Mon Oct 26, 2020 10:08 pm
Forum: Properties of Light
Topic: Tips for knowing what equation to use?
Replies: 5
Views: 74

### Re: Tips for knowing what equation to use?

The way I do it is I just look at what values I've been given and what value I'm asked to solve for. All of these together should fit evenly into one equation. For example if I'm given frequency and asked to find wavelength, I know I have to use (lambda)(frequency) = c. If I'm given velocity of an e...
Mon Oct 26, 2020 12:49 am
Forum: Properties of Electrons
Topic: Electron Transition series for the Hydrogen Atom
Replies: 1
Views: 34

### Electron Transition series for the Hydrogen Atom

For the midterm will we be required to know the Paschen series, or just the Balmer and Lyman series? Also, I'm a bit confused about the Balmer and Lyman series. So the Lyman series shows e- transitions that give off photons in the UV region, and the Balmer series shows e- transitions that give off p...
Sun Oct 25, 2020 1:36 am
Forum: Properties of Electrons
Topic: Sapling Week 2,3,4 #12
Replies: 7
Views: 63

### Re: Sapling Week 2,3,4 #12

I've seen 1.0974 * 10^7 m^-1 given as a rydberg constant online before, but the number Dr. Lavelle gives us is R = 3.28984 × 10^15 Hz. I recommend using that and plugging it into ν = R [1/n1^2 - 1/n2^2]. Then convert frequency into wavelength using (frequency)(lambda) = c. I did that and I got 7.29 ...
Sun Oct 25, 2020 1:30 am
Forum: Administrative Questions and Class Announcements
Topic: Missing equation on Constants and Equations Worksheet
Replies: 2
Views: 25

### Missing equation on Constants and Equations Worksheet

I was looking through the constants and equations sheet on Dr. Lavelle's website and I noticed that the photoelectric effect equation (Ek = hv - work function) doesn't seem to be on there. Is this a mistake, or will we be required to memorize this equation for the midterm?
Sat Oct 24, 2020 12:37 am
Forum: Molarity, Solutions, Dilutions
Topic: Homework Problem Help
Replies: 1
Views: 31

### Re: Homework Problem Help

It's not plausible because as you dilute the solution, the number of moles of X stays the same, but the liters of solution increases. In this case, you diluted the solution a lot, to the point where the molarity was so small that it seems to be 0. In other words, there is still the same amount of mo...
Thu Oct 22, 2020 9:59 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Problem 1B.25
Replies: 3
Views: 69

### Re: Problem 1B.25

Here's my work (\Delta x)(\Delta p)\geq h/4pi (350 x 10^-12 m)(9.11 x 10^-31 kg)(\Delta v) \geq 6.262 x 10^-34/4pi \Delta v = 1.65 x 10^5 m/s If you followed the steps like you said, you probably just made a calculation error, or you might not have converted p...
Thu Oct 22, 2020 9:39 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Clarification on the Rydberg constant
Replies: 5
Views: 36

### Re: Clarification on the Rydberg constant

No, you should use R=3.29*10^15 Hz for both equations. I just looked online and it seems like people say to use R=1.09*10^7 m for 1/lambda= , but the equation we were given in class is frequency = . It's possible that the discrepancy in R constants is due to R=1.09*10^7 including the speed of light ...
Thu Oct 22, 2020 9:34 pm
Forum: Properties of Light
Topic: Energy and intensity of light in both models
Replies: 4
Views: 51

### Re: Energy and intensity of light in both models

I'm not sure about how energy is related to intensity in the wave model, but I know for sure that in the wave model increasing the amplitude results in an increase in energy. Also Olivia I actually think a higher frequency results in a higher energy per photon. For example, ultraviolet photons have ...
Wed Oct 21, 2020 12:39 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Question 20 from Heisenberg Module
Replies: 2
Views: 40

### Re: Question 20 from Heisenberg Module

I did the same thing as Bronson, and if it helps, I remember Dr. Lavelle saying that he wouldn't give us numbers that are too close to the maximum velocity or KE. The midterm problems will likely be similar to this problem, in that one possible answer is very small and the other is very large.
Wed Oct 21, 2020 12:33 am
Forum: Properties of Light
Topic: Longer wavelength means larger wavelength?
Replies: 5
Views: 52

### Re: Longer wavelength means larger wavelength?

I would avoid using the term larger when referring to wavelength because some people might think you're referring to the amplitude of the wave. The distance from peak to peak (or from any one point on a wave to the same point on the next cycle) is the length of the wave. The height of the wave is th...
Sat Oct 17, 2020 12:20 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Audio visual focus module, atomic spectra, Q. 42
Replies: 2
Views: 27

### Audio visual focus module, atomic spectra, Q. 42

Can someone help me solve this problem from the audio visual focus modules?

42. An excited hydrogen atom emits light with a frequency of 1.14 x 10^14 Hz to reach the energy level n = 4. In what principle quantum level did the electron begin?

Options include n=5, n=6, n=4, and n=7.
Wed Oct 14, 2020 11:44 pm
Forum: Student Social/Study Group
Replies: 32
Views: 274

### Re: iPad vs Paper notes

Another option if you're not totally set on getting an Apple device is getting a 2 in 1 laptop. I got the dell xps 13 2 in 1, which switches from laptop to tablet form pretty easily (the screen folds 360 degrees to make the tablet). I like it because I only have to carry one device around, and you c...
Wed Oct 14, 2020 11:36 pm
Forum: Properties of Light
Topic: Light Intensity and Photons
Replies: 8
Views: 75

### Re: Light Intensity and Photons

Actually, I'm pretty sure that using the particle model, the only way to increase the intensity is to increase the number of photons (this makes sense to me when I think about how light with more intensity is brighter, i.e. there is more light). Increasing the amount of energy of each photon just ch...
Tue Oct 13, 2020 11:48 pm
Forum: Quantum Numbers and The H-Atom
Topic: Two Different Energy States
Replies: 4
Views: 41

### Re: Two Different Energy States

Yeah I'm watching the atomic spectra module right now, and it looks like for hydrogen specifically, electrons can be at 2 different energy levels (which correspond to the electron rungs Jaden's talking about). In order for a hydrogen electron to absorb energy and move up an energy level, that energy...
Tue Oct 13, 2020 11:03 pm
Forum: Quantum Numbers and The H-Atom
Topic: Two Different Energy States
Replies: 4
Views: 41

### Re: Two Different Energy States

I don't remember that particular part of the lecture, but I'm pretty sure he's just talking about quanta (packets of energy), and the idea that particles can only generate or absorb electromagnetic radiation in specific packets of energy.
Tue Oct 13, 2020 10:56 pm
Forum: Photoelectric Effect
Topic: Energy from the Light Source
Replies: 1
Views: 18

### Re: Energy from the Light Source

I just looked it up, and it seems that instead of being ejected from the metal, the electron is simply raised to a higher energy state. When it settles back down to its normal energy state, it usually releases the excess energy as heat. (A common example of this is a black shirt getting warmer in th...
Wed Oct 07, 2020 5:24 pm
Forum: Balancing Chemical Reactions
Topic: Textbook Problem L 35
Replies: 5
Views: 51

### Re: Textbook Problem L 35

I'm also confused why it says 2.50 t of NaBr is produced. What does t represent?
Mon Oct 05, 2020 9:56 pm
Forum: SI Units, Unit Conversions
Topic: Conversion of grams to moles and millimoles to moles.
Replies: 9
Views: 101

### Re: Conversion of grams to moles and millimoles to moles.

I'd like to add that when converting anything from one unit to another or when doing stoichiometry, the easiest way to make sure you're doing it correctly is to ensure that all the units besides the unit you want your answer to be in are cancelled out. For example, if you're converting from grams to...
Mon Oct 05, 2020 9:47 pm
Forum: Limiting Reactant Calculations
Topic: Fundamentals M19
Replies: 5
Views: 35

### Re: Fundamentals M19

I'd like to add that the main reason you can't find the moles of the oxygen in the caffeine directly from the moles of oxygen in the products isn't because oxygen is present in 2 of the products (if this were the case, you could just add the moles of oxygen from each product together). Actually, it'...
Mon Oct 05, 2020 9:36 pm
Forum: Molarity, Solutions, Dilutions
Topic: molar mass vs molecular mass
Replies: 6
Views: 71

### Re: molar mass vs molecular mass

I'd also like to add that you can say atomic mass when talking about one element (ex - the atomic mass of carbon is 12.01 u). However, when talking about a compound, such as CO2, you must use the term molecular mass when you want to talk about the mass of one molecule of a compound.
Mon Oct 05, 2020 9:26 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: precision for molar masses
Replies: 14
Views: 112

### Re: precision for molar masses

Since 14.007 has 5 sig figs, and 14.01 only has 4, if you want to include 5 sig figs in your answer (which you can only do if you know all the other values you're using to 5 sig figs) you have to use 14.007. If you use 14.01 you almost certainly will not get the same answer. However, if you round yo...
Mon Oct 05, 2020 9:16 pm
Forum: Significant Figures
Topic: Sig Figs for elements on Periodic table
Replies: 14
Views: 141

### Re: Sig Figs for elements on Periodic table

Sorry for the extra post, but I'd just like to re-emphasize for Jason that as long as your final answer is 4 sig figs or less , you won't be off at all. If your final answer is 5 sig figs, you'd have to use a molar mass accurate to 5 sig figs to get a fully accurate answer.
Mon Oct 05, 2020 9:11 pm
Forum: Significant Figures
Topic: Sig Figs for elements on Periodic table
Replies: 14
Views: 141

### Re: Sig Figs for elements on Periodic table

I'm pretty sure it would not matter how many sig figs are on the periodic table because those values are known. Instead you would determine the number of sig figs from any given or measured values in the problem. For example, if it said 1.53 mol of CO2, then you would use 3 sig figs throughout the ...