## Search found 66 matches

Mon Jan 11, 2021 11:47 am
Forum: Administrative Questions and Class Announcements
Topic: Upvoting responses
Replies: 2
Views: 32

### Re: Upvoting responses

I see a small upwards pointing arrow in the lower right corner of each reply, but I'm not sure if students can click on it.
Mon Jan 11, 2021 11:45 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Sapling 5J.5 d)
Replies: 3
Views: 30

### Re: Sapling 5J.5 d)

Like the previous answer stated I think it's an issue with the textbook problem and not your conceptual understanding, because you're approaching it correctly! My textbook also had 2HD(g) <--> H2(g) + D2(g).
Mon Jan 11, 2021 11:39 am
Forum: Administrative Questions and Class Announcements
Topic: Audio-Visual Focus-Topics
Replies: 2
Views: 22

### Re: Audio-Visual Focus-Topics

Yes, I believe so! Everything that's posted on the Chem 14B class website is what's offered.
Mon Jan 11, 2021 11:33 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook 5I.3
Replies: 3
Views: 13

### Re: Textbook 5I.3

I think you're using the wrong K. I used K=160 for H2 + I2 <---> 2HI @ 500K and I got 2.1 * 10^-5 M. Hope this helps!
Mon Jan 11, 2021 11:21 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Large Kc for Cubic Equations
Replies: 6
Views: 33

### Re: Large Kc for Cubic Equations

It is possible to have large Kc values with the Kc expression being cubic. The cubic nature of the expression depends on what information is given in the problem. However, I don't think we'll get problems like this on any exams just because as you said it does get more complicated to solve since we ...
Mon Jan 11, 2021 11:14 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook Problem 5.35
Replies: 1
Views: 27

### Re: Textbook Problem 5.35

Hi! For this problem, the first thing you should do is create an ICE table based on the graph. The graph tells you the initial concentrations of A (about 28 M), B (0 M), and C (0 M), and it also shows you the equilibrium concentrations of A (about 18 M), B (5 M), and C (10 M). Based on the differenc...
Mon Jan 04, 2021 2:23 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Post Module 1A #26
Replies: 2
Views: 16

### Re: Post Module 1A #26

The correct answer is A, equilibrium constants are useful because they are one number that gives us information about the relative concentrations of reactant and product. K is the ratio of the equilibrium concentrations of products to the reactants raised to their respective stoichiometric coefficie...
Mon Jan 04, 2021 2:19 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Module 1A #12
Replies: 2
Views: 16

### Re: Module 1A #12

You're correct, C is false! At equilibrium, the forward and reverse reactions do still occur, just at the same rate.
Mon Jan 04, 2021 12:42 pm
Forum: Administrative Questions and Class Announcements
Topic: 14B Discussion Sections
Replies: 4
Views: 49

### 14B Discussion Sections

When will TAs officially be assigned? My discussion section is tomorrow but I don't see who my TA is on myUCLA.
Mon Jan 04, 2021 12:35 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5J.5 (part d) Textbook Problem
Replies: 4
Views: 29

### Re: 5J.5 (part d) Textbook Problem

I also think this might be an error in the solutions. Prof Lavelle mentioned in one of the module videos that one of the situations in which there would be no change is if the pressure was increased by adding an inert gas (which doesn't affect the volume and therefore the concentration), but in this...
Mon Jan 04, 2021 12:24 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Chem Equilibrium Pt.4 Post-Assess
Replies: 4
Views: 27

### Re: Chem Equilibrium Pt.4 Post-Assess

Hi! Like the previous response stated, a negative delta H indicates an exothermic reaction, as heat is being released/lost from the reaction system. You would consider the heat that is released to be a product of the reaction. Therefore, if temperature is increased, you are essentially increasing a ...
Mon Dec 07, 2020 10:59 am
Forum: Quantum Numbers and The H-Atom
Topic: probabilty of finding e- in a location
Replies: 6
Views: 53

### Re: probabilty of finding e- in a location

^^ Yeah we only did conceptual stuff, we don't need to know how to calculate the exact probability. However, it might be helpful to know how many nodes (areas with 0 probability of electron density) each subshell in an atom has. The total number of nodes in a subshell = n-1, # of angular nodes = l, ...
Mon Dec 07, 2020 10:54 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: practice problem 1D 19
Replies: 2
Views: 18

### Re: practice problem 1D 19

Yes, those are correct! The number of orbitals in a subshell is equal to the number of possible ml values for the specific value of l. For 4p, l = 1 so ml = -1, 0, 1; therefore 4p has 3 orbitals.
Mon Dec 07, 2020 10:40 am
Forum: Conjugate Acids & Bases
Topic: What is a conjugate acid or base?
Replies: 5
Views: 40

### Re: What is a conjugate acid or base?

A conjugate acid is the resulting species when a base accepts a proton, and a conjugate base is the species that results when an acid gives off a proton. For example, the conjugate acid of the base NH3 is NH4+, as NH3 + H+ --> NH4+. The conjugate base of H2SO4 is HSO4-, since H2SO4 donating a proton...
Mon Dec 07, 2020 9:49 am
Forum: Hybridization
Topic: Book Problem F1
Replies: 3
Views: 33

### Re: Book Problem F1

By relative orientations I think they mean the relative arrangement of the hybrid orbitals. For sp3, each of the 4 hybrid orbitals points to one corner of a tetrahedron. For sp2, each hybrid orbital points to a corner of an equilateral triangle. Hope this helps!
Mon Dec 07, 2020 9:47 am
Forum: Biological Examples
Topic: Difference between Myoglobin and heme complex
Replies: 8
Views: 95

### Re: Difference between Myoglobin and heme complex

I agree with the previous answer, the heme complex + the hystidine protein make up myoglobin.
Mon Nov 30, 2020 11:09 am
Forum: General Science Questions
Replies: 26
Views: 269

Yeah I think you have to meet with your TA to go over your midterm!
Mon Nov 30, 2020 11:00 am
Forum: Naming
Topic: Formula from Naming
Replies: 3
Views: 28

### Re: Formula from Naming

The textbook has a set of rules in Focus 9C.1 (Toolbox 9C.1) for writing the formulas and naming the compounds! For writing the formula, the textbook says to write the chemical symbol of the central metal atom first and then write the symbols of the ligands in alphabetical order. For different ligan...
Mon Nov 30, 2020 10:57 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Equatorial/ Axial Planes
Replies: 14
Views: 73

### Re: Equatorial/ Axial Planes

You would place a lone pair on the equatorial vs axial plane based on which position would limit the number of 90 degree interactions with the other atoms in the molecule, since these interactions are unfavorable.
Mon Nov 30, 2020 10:54 am
Forum: Naming
Topic: Using ido or o
Replies: 24
Views: 126

### Re: Using ido or o

Just a heads up, the textbook uses the -ido convention but the Sapling HW uses o!
Mon Nov 30, 2020 10:52 am
Forum: Naming
Topic: Sapling Homework W9 Problem#1
Replies: 5
Views: 54

### Re: Sapling Homework W9 Problem#1

Hi! I had trouble with this one too, but the book has a helpful list of rules in Focus 9C.1 for naming coordination compounds/complexes. First, everything enclosed by the brackets is part of the complex ion. The complex ion has an overall charge of +1, as Cl is -1 and the whole coordination compound...
Sat Nov 28, 2020 11:05 pm
Forum: Hybridization
Topic: Normalized vs Unnormalized hybrid orbitals
Replies: 3
Views: 30

### Re: Normalized vs Unnormalized hybrid orbitals

So I have no clue, so I tried to research what it might be, and I'm getting conflicting answers, one of which says that it's simply perpendicular to each other (normal to each other), and the other of which says they are standardized to one another. The first definition makes the most sense to me, ...
Sat Nov 28, 2020 5:53 pm
Forum: Hybridization
Topic: Normalized vs Unnormalized hybrid orbitals
Replies: 3
Views: 30

### Normalized vs Unnormalized hybrid orbitals

What does it mean for hybrid orbitals to be normalized vs unnormalized?
Sat Nov 28, 2020 11:21 am
Forum: Ionic & Covalent Bonds
Topic: lone pairs -polar molecule
Replies: 10
Views: 92

### Re: lone pairs -polar molecule

I don’t think you can assume that any molecule with a central atom that has lone pairs is polar. For example, XeF2 is non polar, and it has 3 lone pairs on the central atom. The lone pairs are arranged at 120 degrees to each other and the F-Xe-F bond angle is 180 degrees, so there is a 0 net dipole ...
Mon Nov 23, 2020 2:11 pm
Forum: Administrative Questions and Class Announcements
Topic: Discussion
Replies: 2
Views: 27

### Re: Discussion

I don't think there will be discussions on Thursday or Friday, but I'm not sure if students in those discussions will have to make it up.
Mon Nov 23, 2020 1:59 pm
Forum: Hybridization
Topic: regions of electron density
Replies: 7
Views: 52

### Re: regions of electron density

Just to add on, an unpaired electron on a radical like NO2 is also considered to be a region of electron density.
Mon Nov 23, 2020 12:58 pm
Forum: Hybridization
Topic: Energy Level of sp3d and sp3d2
Replies: 2
Views: 24

### Re: Energy Level of sp3d and sp3d2

Dr. Lavelle mentioned that the energy of the hybrid orbitals is the average of the energies of the atomic orbitals used.
Mon Nov 23, 2020 12:54 pm
Forum: Ionic & Covalent Bonds
Topic: Polar/ Nonpolar
Replies: 23
Views: 164

### Re: Polar/ Nonpolar

FionaHunter21 wrote:Are there dipole moments between all atoms with a difference in electronegativity or just the polar bonds?

I believe all bonded atoms with a difference in electronegativity exhibit a dipole, but the magnitude/strength of the dipole is given by mu = |q|*d (charge * distance between the atoms).
Mon Nov 23, 2020 12:49 pm
Forum: Determining Molecular Shape (VSEPR)
Replies: 4
Views: 39

I agree with the previous answer, Dr. Lavelle mentioned in one of his lectures that the unpaired electron in radicals like NO2 is considered a region of electron density.
Mon Nov 16, 2020 1:14 pm
Forum: Trends in The Periodic Table
Topic: Z effective
Replies: 2
Views: 32

### Re: Z effective

The effective nuclear charge refers to the protons/nucleus of an atom, not the electrons. In terms of periodic trends, the effective nuclear charge increases as you go across a period because the atomic number increases and electrons are being added to the same energy level. It decreases down a grou...
Mon Nov 16, 2020 1:05 pm
Forum: Lewis Structures
Topic: Identifying lewis acids and bases
Replies: 5
Views: 50

### Re: Identifying lewis acids and bases

Cations, molecules with electron deficient central atoms (like BF3), and molecules with polar double bonds (like CO2) tend to be lewis acids since they are more likely to accept an electron pair. Anions and molecules with lone pairs (like H2O) tend to be lewis bases since they have electrons to dona...
Mon Nov 16, 2020 1:01 pm
Forum: Dipole Moments
Topic: Dipole moment vs dipole bond
Replies: 5
Views: 35

### Re: Dipole moment vs dipole bond

A dipole moment is a partial positive charge and partial negative charge within a molecule, though the molecule is as a whole electrically neutral. For example, the hydrogens in H2O have a partial positive charge and the oxygen has a partial negative charge due to the electronegativity difference be...
Mon Nov 16, 2020 12:53 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: Polarizability
Replies: 3
Views: 27

### Re: Polarizability

To add on, in terms of periodic trends polarizability tends to increase as you go down a group because the atomic radius and the number of electrons increase.
Mon Nov 16, 2020 12:47 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Periodic Table Trends
Replies: 4
Views: 25

### Re: Periodic Table Trends

For anions, polarizability increases as you go down a group since the atomic radius and number of electrons increases and the effective nuclear charge decreases. In general, the larger the radius and the more electrons an atom has, the more polarizable. For polarizing power, the smaller the atomic r...
Mon Nov 09, 2020 1:27 pm
Forum: Bond Lengths & Energies
Topic: London (dispersion) force
Replies: 3
Views: 27

### Re: London (dispersion) force

London dispersion forces are induced dipole-induced-dipole interactions. Basically, when non-polar molecules collide their electron densities are shifted, forming a temporary delta negative and delta positive side. This induces the neighboring molecule to form a temporary dipole as well and produces...
Mon Nov 09, 2020 1:11 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: Lecture 17 Question (IMF)
Replies: 3
Views: 27

### Re: Lecture 17 Question (IMF)

I believe Professor Lavelle mentioned it's the energy per mole of the given interaction. For example, if there was 1 mole of Na+ and Cl- interactions, the amount of energy released due to the ion-ion interactions would be 250 kJ.
Mon Nov 09, 2020 1:07 pm
Forum: Ionic & Covalent Bonds
Topic: Temporary vs Permanent Dipole Moments
Replies: 2
Views: 23

### Re: Temporary vs Permanent Dipole Moments

An example of a molecule with a permanent dipole is H2O; the difference in electronegativity between the O and Hs causes the electrons to be pulled towards O, creating a permanent delta negative and delta positive side. Temporary dipoles occur when molecules that are otherwise non-polar, like N2, co...
Mon Nov 09, 2020 1:01 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Can an Anion be Polarizing
Replies: 4
Views: 60

### Re: Can an Anion be Polarizing

I think the electrons on the anion are referred to as polarizable and the cation as polarizing and not the other way around because the protons in the nucleus of the cation don't "move" due to the attractive force they experience from the electrons of the anion. It is the electrons that ar...
Mon Nov 09, 2020 12:56 pm
Forum: Bond Lengths & Energies
Topic: Negative energies? [ENDORSED]
Replies: 7
Views: 75

### Re: Negative energies?[ENDORSED]

In terms of thermodynamics, if you think about the molecule/compound as a system, anything that increases the energy of the system, for example putting in energy to break bonds, makes delta E positive. When energy is released, delta E is negative. The intermolecular/interionic interactions have nega...
Mon Nov 02, 2020 4:06 pm
Forum: Resonance Structures
Topic: Delocalization of Electrons
Replies: 2
Views: 20

### Re: Delocalization of Electrons

For non-resonance structures, electrons are localized.
Mon Nov 02, 2020 4:04 pm
Forum: Lewis Structures
Topic: Bent or Angular?
Replies: 18
Views: 426

### Re: Bent or Angular?

I believe angular is 2 atoms bonded to the central atom with 1 lone pair, and bent is 2 atoms bonded to the central atom with 2 lone pairs.
Mon Nov 02, 2020 3:42 pm
Forum: General Science Questions
Topic: Finals
Replies: 39
Views: 362

### Re: Finals

Will the final also be multiple choice?
Mon Nov 02, 2020 3:41 pm
Forum: Resonance Structures
Topic: Energy and Stability in Delocalization
Replies: 3
Views: 31

### Re: Energy and Stability in Delocalization

Here is the textbook's explanation for why it increases stability (it's in Focus 2B): "As well as delocalizing electrons over the atoms, resonance also lowers the energy below that of any single contributing structure and helps to stabilize the molecule. This lowering of energy occurs for quant...
Mon Nov 02, 2020 3:25 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Shells
Replies: 7
Views: 64

### Re: Electron Shells

The angular momentum quantum number l, which tells us about the subshells in each shell, is determined by the principle quantum number (n=3 in this case). For n=3, l can be 0...n-1 which is 0, 1, and 2, corresponding to s, p, and d.
Mon Nov 02, 2020 2:50 pm
Forum: Resonance Structures
Topic: Delocalization of Electron
Replies: 2
Views: 41

### Re: Delocalization of Electron

Delocalized electrons are electrons that do not "belong" to a particular atom or are not associated with a specific bond in the molecule. Here is the textbook's explanation for why it increases stability (it's in Focus 2B): "As well as delocalizing electrons over the atoms, resonance ...
Mon Oct 26, 2020 12:42 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Subshell Definition
Replies: 9
Views: 60

### Re: Subshell Definition

Within a particular energy level (n), all electrons with the same angular momentum quantum number (l) are in the same sub-shell, and all electrons with the same n, l, and ml (magnetic quantum number) are in the same orbital.

Hope this helps!
Mon Oct 26, 2020 12:16 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Replies: 2
Views: 30

What is the difference between radial and angular nodes, and how many do each of the orbitals (s, p, d, f) have?
Mon Oct 26, 2020 12:11 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Determining Spin in orbitals [ENDORSED]
Replies: 5
Views: 56

### Re: Determining Spin in orbitals[ENDORSED]

He drew 3 up-spin electrons first because according to Hund's Rule, electrons occupy empty orbitals in the same sub-shell before pairing up. As for why the up-spin electrons are drawn first, I think it just has to do with convention.
Mon Oct 26, 2020 12:04 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect [ENDORSED]
Replies: 4
Views: 79

### Re: Photoelectric Effect[ENDORSED]

If you think about EM radiation as a wave of oscillating electric and magnetic fields that are perpendicular to each other, the frequency is related to how the electric field changes, or oscillates, with time. The greater the frequency, the faster the field changes/oscillates. The smaller the freque...
Mon Oct 26, 2020 11:57 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Orbital vs. Subshell
Replies: 13
Views: 93

### Re: Orbital vs. Subshell

Within a particular energy level (n), all electrons with the same angular momentum quantum number (l) are in the same sub-shell, and all electrons with the same n, l, and ml (magnetic quantum number) are in the same orbital. Here's an explanation with a helpful graphic: https://chemistry.stackexchan...
Mon Oct 19, 2020 2:26 pm
Forum: Administrative Questions and Class Announcements
Topic: Multiple choice test?
Replies: 7
Views: 70

### Re: Multiple choice test?

That's what I heard too, some of the TAs said it was all multiple choice.
Mon Oct 19, 2020 2:23 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Textbook Problem 1B27
Replies: 6
Views: 49

### Re: Textbook Problem 1B27

Delta v should be 10 m/s. I believe this is an error in the book's solution. Here's a full list of errors in the solution manual:

https://lavelle.chem.ucla.edu/wp-conten ... rs_7Ed.pdf
Mon Oct 19, 2020 2:03 pm
Forum: Properties of Light
Topic: Properties of Light
Replies: 5
Views: 26

### Re: Properties of Light

As the previous answer stated, the equation is E = hv. The photoelectric effect demonstrated that light exhibits properties of particles and also demonstrated the relationship between energy and frequency of photons.
Mon Oct 19, 2020 1:18 pm
Forum: Administrative Questions and Class Announcements
Replies: 9
Views: 91

^^ Thanks!
Mon Oct 19, 2020 1:16 pm
Forum: Photoelectric Effect
Topic: Circular Standing Wave model
Replies: 2
Views: 34

### Re: Circular Standing Wave model

The circular standing wave model is just a math model that was developed to reconcile electrons having wave-like properties and having quantized energy states. In this model, each stable circular standing wave (with whole number wavelengths) around the nucleus represents an energy level (n=1, 2, 3.....
Mon Oct 19, 2020 1:06 pm
Forum: Administrative Questions and Class Announcements
Replies: 9
Views: 91

Does anyone know if we'll also be given the wavelengths corresponding to the different regions of the EM spectrum, or will we need to just know it?
Mon Oct 12, 2020 5:04 pm
Forum: Properties of Light
Topic: video modules
Replies: 10
Views: 95

### Re: video modules

They're not mandatory but they are helpful, and the videos are pretty short so it won't take too much time to check them out!
Mon Oct 12, 2020 4:02 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Identifying n1 and n2
Replies: 4
Views: 60

### Identifying n1 and n2

How do you identify which energy level is n1 and which is n2 for frequency = R(1/(n1)^2 - 1/(n2)^2)? Is n1 always the initial energy level and n2 always the final energy level?
Mon Oct 12, 2020 12:38 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Spectral Lines and Series
Replies: 1
Views: 41

### Spectral Lines and Series

Why do spectral lines in the same series (Balmer series, Lyman series, etc.) always represent transitions ending with the same final energy level?
Mon Oct 12, 2020 12:10 pm
Forum: Photoelectric Effect
Topic: Lecture 5
Replies: 5
Views: 90

### Re: Lecture 5

According to the particle model of light, the intensity of light is proportional to the number of photons, which translates into how bright the light is. Intensity is not related to wavelength.
Mon Oct 12, 2020 11:57 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Rounding when the last digit is 5
Replies: 6
Views: 78

### Re: Rounding when the last digit is 5

Yes, I think that's the rule we're expected to follow. On the Chem 14A website, Professor Lavelle posted "Everything you want to know about Sig Fig" under the Course Materials header, and the 2nd page summarizes rules for rounding, which include the nearest even number rule. https://lavell...
Mon Oct 05, 2020 3:37 pm
Forum: Administrative Questions and Class Announcements
Topic: Submitting HW on Sapling
Replies: 5
Views: 60

### Re: Submitting HW on Sapling

I don't think there is a way to submit the problems. I think as long as you have 1 attempt for each question, you're fine.
Mon Oct 05, 2020 12:37 pm
Forum: Molarity, Solutions, Dilutions
Topic: Question about Moles of Solute
Replies: 10
Views: 82

### Re: Question about Moles of Solute

For dilution, you start with a solution of a certain concentration and just add solvent to decrease the concentration. The only thing that's changing is total volume of the solution, the moles of solute always stays the same.
Mon Oct 05, 2020 12:30 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Replies: 31
Views: 363

Typically when you need to convert moles of something into atoms or molecules, you would use Avogadro's #. Ex: 0.50 mol C * (6.022E23 atoms C / 1mol C) = 3.0E23 atoms C
Mon Oct 05, 2020 12:14 pm
Forum: Molarity, Solutions, Dilutions
Topic: Process of Molarity Calculation
Replies: 6
Views: 77

### Re: Process of Molarity Calculation

You would use the first method and directly divide the moles of KCl by the final volume since the moles of solute remain constant through the process, as a previous answer mentioned. In terms of when to use the M1V1 = M2V2 equation, you would typically use it for problems where you have to calculate...
Mon Oct 05, 2020 10:16 am
Forum: Significant Figures
Topic: Significant Figures for Calculations with Molar Masses
Replies: 5
Views: 93

### Significant Figures for Calculations with Molar Masses

Are molar masses considered measured values or defined constants?