Search found 100 matches
- Mon Mar 08, 2021 10:44 pm
- Forum: Administrative Questions and Class Announcements
- Topic: DAYLIGHT SAVINGS TIME!
- Replies: 12
- Views: 1306
Re: DAYLIGHT SAVINGS TIME!
Thanks for the reminder!! I'm from Arizona and we don't have Daylight savings so I always forget.
- Mon Mar 08, 2021 10:39 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Constants and Equations Sheet
- Replies: 6
- Views: 333
Re: Constants and Equations Sheet
Nothing's been updated as far as I know! It seems to include all the recent equations we learned (rate laws, half life, arrhenius), so I think it'll be the same one as midterm 2. Plus in chem 14a, we only had 1 equation sheet throughout.
- Mon Mar 08, 2021 10:27 pm
- Forum: Student Social/Study Group
- Topic: How do you deal with burnout?
- Replies: 144
- Views: 12719
Re: How do you deal with burnout?
I feel like burnout has definitely hit me hard these past few weeks. I've been finding it hard to actually take the time and learn the material instead of just taking notes head empty. A method that works for me is to write out a list of tasks on a sticky sticky note and then crossing them off as I ...
- Mon Mar 08, 2021 10:17 pm
- Forum: Student Social/Study Group
- Topic: chem community points
- Replies: 23
- Views: 1038
Re: chem community points
We should have 50 posts by Sunday 11:59pm I believe.
- Mon Mar 08, 2021 10:15 pm
- Forum: Student Social/Study Group
- Topic: Final Jitters
- Replies: 457
- Views: 329216
Re: Final Jitters
I try do do as many practice problems (both homework and textbook problems) as I can and get a good night of sleep beforehand. For some reason, I find eating a piece being a test helpful? It helps me calm down.
- Tue Mar 02, 2021 9:46 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Activation Energy
- Replies: 17
- Views: 808
Re: Activation Energy
Activation energy and enthalpy aren't interchangeable. I believe later on in the lectures, we'll see how the two are used together though.
- Tue Mar 02, 2021 9:36 pm
- Forum: Balancing Redox Reactions
- Topic: How to Determine if a Reaction is in Basic or Acidic Solution?
- Replies: 53
- Views: 2765
Re: How to Determine if a Reaction is in Basic or Acidic Solution?
They will usually explicitly state if the solution is acidic or basic in the problem luckily! At least this is what I've noticed based on the practice problems.
- Tue Mar 02, 2021 9:28 pm
- Forum: General Rate Laws
- Topic: First order reactions
- Replies: 7
- Views: 412
Re: First order reactions
Yup! A 1st order reaction can have more than 1 reactant as long as only 1 of the reactants affects the rate of reaction (1st order). For example, if rate = k [A]^n [B]^m where n=1 and m=0 and A and B are reactants, then it's considered a first order reaction!
- Tue Mar 02, 2021 9:21 pm
- Forum: Zero Order Reactions
- Topic: Half life
- Replies: 19
- Views: 851
Re: Half life
You could also use t1/2 = [A]0/2k!
- Tue Mar 02, 2021 8:35 pm
- Forum: General Rate Laws
- Topic: Number of Reactants
- Replies: 26
- Views: 991
Re: Number of Reactants
Having more than 3 reactants can definitely happen, but we most likely won't have to worry about for this class!
- Mon Feb 22, 2021 10:32 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Advice from a Medical Student - Part II [ENDORSED]
- Replies: 298
- Views: 241143
Re: Advice from a Medical Student - Part II [ENDORSED]
Thank you so much for the part 2! Reading this is really inspiring and motivating, especially right now during week 8. Wishing you the best of luck!!
- Mon Feb 22, 2021 10:21 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Le Chatlier's with Cell Potentials
- Replies: 3
- Views: 181
Re: Le Chatlier's with Cell Potentials
Yes, Le Chatlier's principle still applies for redox reactions. Because E = E0 - RT/nF lnQ where Q is the reaction quotient (concentration of products/reactants), changing the concentration will affect voltage potential as well.
- Mon Feb 22, 2021 9:54 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Sig Figs
- Replies: 7
- Views: 518
Re: Sig Figs
Yup, it does! We probably won't be tested on sig figs though which is nice
- Mon Feb 22, 2021 9:52 pm
- Forum: Balancing Redox Reactions
- Topic: Balancing
- Replies: 9
- Views: 442
Re: Balancing
yes, E's value only changes when the reaction is flipped, in which case you multiply by -1. Otherwise, E remains constant.
- Mon Feb 22, 2021 9:44 pm
- Forum: Balancing Redox Reactions
- Topic: e- in Redox Reactions
- Replies: 11
- Views: 503
Re: e- in Redox Reactions
Yup! A big part of balancing redox reactions is making sure the number of electrons lost in the oxidation half reaction equals the number of electrons gained in the reduction half reaction.
- Sat Feb 20, 2021 5:30 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Solids and Liquids?
- Replies: 26
- Views: 1191
Re: Solids and Liquids?
Only gases apply for Le Chatelier. For example, if pressure increased, only the concentration of gases would be affected since they can be compressed unlike solids, liquids, and gases.
- Sat Feb 20, 2021 5:23 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Difference between E and E^o
- Replies: 4
- Views: 745
Re: Difference between E and E^o
E changes based on the concentration of the products and reactants since E = E0 - (RT/nF)ln(Q) where Q is the reaction quotient.
- Sat Feb 20, 2021 5:15 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: anode and cathode L/R
- Replies: 14
- Views: 579
Re: anode and cathode L/R
I think the anode is usually on the left and the cathode is on the right, but it isn't a strict rule. It makes the diagram simpler since it's more consistent. If you reversed everything else as well (ex. flow of electrons), the anode can be on the right and the cathode on the left.
- Sat Feb 20, 2021 5:10 pm
- Forum: Balancing Redox Reactions
- Topic: Sapling #3
- Replies: 4
- Views: 358
Re: Sapling #3
I don't think he's covered it just yet, but he probably will either Monday or Wednesday. The organic chemistry tutor on youtube does a great job explaining it though, if you want to get ahead! https://www.youtube.com/watch?v=fdbrhQAM9Gw
- Sat Feb 20, 2021 5:05 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidation Numbers
- Replies: 9
- Views: 523
Re: Oxidation Numbers
Hi! For MnO4-, the overall oxidation number is -1 and the oxidation number of O is always -2 (except for in peroxide). Knowing that, we can calculate the oxidation number of Mn. Mn + 4(-2) = -1. The oxidation number of Mn in MnO4- is +7. On the other hand, the oxidation number of Mn2+ is 2+ since th...
- Mon Feb 08, 2021 11:26 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: 2 deltaG equations
- Replies: 6
- Views: 418
Re: 2 deltaG equations
Both will help solve for the same delta G value! It mainly depends on what they give you to work with. Since they solve for the same thing, you can also set them equal to one another
- Mon Feb 08, 2021 11:17 pm
- Forum: Ideal Gases
- Topic: Chem BL
- Replies: 107
- Views: 6982
Re: Chem BL
I'm only taking BL next quarter, but I know people who are taking both BL and C this quarter. It seems pretty manageable based on what I've heard!
- Mon Feb 08, 2021 11:12 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Useful Summary of Thermodynamic Definitions
- Replies: 55
- Views: 18249
Re: Useful Summary of Thermodynamic Definitions
Thank you so much! I was having a hard time memorizing all of them, this really helps!
- Mon Feb 08, 2021 11:11 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Different R Constants
- Replies: 14
- Views: 652
Re: Different R Constants
As others have said, it helps to keep track of the units and make sure they all cancel out. .00826 is used when pressure is in terms of atm and volume is in terms of L. 8.314 is used when pressure is in terms of Pa and volume is in terms of m^3. 8.314 J/mol K is the SI unit form of R and is generall...
- Mon Feb 08, 2021 11:04 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Entropy changes during phase changes
- Replies: 3
- Views: 160
Re: Entropy changes during phase changes
During phase changes, the temperature stays constant, so we use deltaS = q/T. When temperature is changing we use deltaS = n*C*ln(T2/T1).
- Mon Feb 01, 2021 10:26 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Tips to drawing out molecules to determine enthalpy changes.
- Replies: 8
- Views: 444
Re: Tips to drawing out molecules to determine enthalpy changes.
Doing the Chem 14A problems for the textbook definitely help! For me at at least, paying attention to formal charge really helps with making sure the structure is correct, but the more you practice and draw, the more intuitive it gets!
- Mon Feb 01, 2021 10:14 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Negative Heat Capacities
- Replies: 9
- Views: 347
Re: Negative Heat Capacities
Heat capacities can't be negative because thermal energy/heat and temperature have a direct relationship. For temperature to increase, the energy must be added to the system.
- Mon Feb 01, 2021 10:05 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Work-/+
- Replies: 9
- Views: 349
Re: Work-/+
If work is done on the system it's positive, for example compressing a container. If work is done by the system it's negative, for example a gas pushing on a container, leading to the container's volume increasing.
- Mon Feb 01, 2021 9:55 pm
- Forum: Phase Changes & Related Calculations
- Topic: Why does steam cause severe burns?
- Replies: 22
- Views: 1547
Re: Why does steam cause severe burns?
Steam has more (thermal) energy compared to boiling water. A lot of energy is required to break/weaken the hydrogen bonds in water so that it can transform into vapor. In addition, once water has transformed to steam/vapor, the vapor can absorb even more energy. Steam releases a lot more energy than...
- Mon Feb 01, 2021 9:47 pm
- Forum: Phase Changes & Related Calculations
- Topic: Boiling water
- Replies: 25
- Views: 2657
Re: Boiling water
Water molecules have hydrogen bonds between then. This keeps them relatively close together due to the attraction between molecules. When water is boiled, energy from the heat allows these hydrogen bonds to break/weaken. As a result, the vapor molecules can be much farther from one another.
- Tue Jan 26, 2021 10:07 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: change in celsius = change in kelvin
- Replies: 22
- Views: 7462
Re: change in celsius = change in kelvin
Kelvin = (Celcius + 273). Say that an object is originally x1 degrees, but is now x2 degrees. If we were to calculate the change in temp, it would equal x2-x1. If we were to convert these temperatures to kelvin, the initial temp = x1 + 273 and the final temp = x2 +273. Delta T = (x1 + 273) - (x2 + 2...
- Tue Jan 26, 2021 9:55 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Correct units for Standard Reaction Enthalpy
- Replies: 7
- Views: 230
Re: Correct units for Standard Reaction Enthalpy
I believe that kJ/mol is the correct unit standard reaction enthalpy since more moles of a molecule would either release more energy (for most) or require more energy.
- Tue Jan 26, 2021 9:46 pm
- Forum: Phase Changes & Related Calculations
- Topic: calculator/ calcutation error
- Replies: 5
- Views: 242
Re: calculator/ calcutation error
I would try using the answer button, which equals the value of your previous answer, if your calculator has one. This way you might face less rounding errors from your calculator since it should store the exact value. Hope you're able to resolve this issue soon!
- Tue Jan 26, 2021 9:34 pm
- Forum: Phase Changes & Related Calculations
- Topic: Midterm Scratch Paper? [ENDORSED]
- Replies: 5
- Views: 270
Re: Midterm Scratch Paper? [ENDORSED]
Scratch paper was allowed last quarter, and it's probably the same this quarter. You just have to show your TA that there's nothing written on it before hand.
- Tue Jan 26, 2021 9:31 pm
- Forum: Phase Changes & Related Calculations
- Topic: midterm respondus
- Replies: 19
- Views: 726
Re: midterm respondus
Yup as others have said, just download it and you should be good to go! My TA had us take a mini quiz with it to make sure it works. Once the midterm is available on CCLE, there should be a launch lockdown browser button in blue which will activate it and show the exam!
- Tue Jan 19, 2021 4:30 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Total Pressure Significance
- Replies: 4
- Views: 217
Re: Total Pressure Significance
I can't think of a scenario where we would use total pressure as is, but as others have said, there could be a problem where we would need to find a partial pressure given the total pressure.
- Tue Jan 19, 2021 4:10 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: A + B
- Replies: 5
- Views: 273
Re: A + B
Yup! If there's no note saying that A, B, or C shouldn't be factored into the equation, then it should be safe to assume they're either gases or aqueous solutions!
- Tue Jan 19, 2021 4:03 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Moles vs Concentrations in ICE Box
- Replies: 21
- Views: 695
Re: Moles vs Concentrations in ICE Box
I prefer putting the concentrations into the ice box just so that I don't forget to it later on.
- Tue Jan 19, 2021 3:58 pm
- Forum: Ideal Gases
- Topic: Gas Constant Value
- Replies: 43
- Views: 1365
Re: Gas Constant Value
Hi! The value we use for R generally depends on the units! .08206 (L atm)/(mol K) and 8.314 J/(mol K) are probably the ones we'll use most tho. Just make sure that the units on the right and left are the same, and you'll be good!
- Tue Jan 19, 2021 3:51 pm
- Forum: Ideal Gases
- Topic: Omitting solid/liquid
- Replies: 19
- Views: 636
Re: Omitting solid/liquid
The concentration for solids and liquids are fixed, unlike gases or aqueous solutions. Since the initial and final concentrations for solids and liquids are about the same, they would cancel out anyways in the K equation, so we omit them altogether.
- Wed Jan 13, 2021 11:09 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Getting two positive x values when using quadratic
- Replies: 43
- Views: 4474
Re: Getting two positive x values when using quadratic
Try plugging both x values back into the concentration equations from the ICE table and see if they make sense. Usually one of the values will produce a negative concentration value which is impossible so we go with the other one. For example, if the concentration of a compound once it reaches equil...
- Wed Jan 13, 2021 10:54 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Increase in Pressure
- Replies: 31
- Views: 661
Re: Increase in Pressure
Pressure only applies to gases, especially in the context of volume changing. The volume of aqueous solutions can't change, but the volume of gases can.
- Wed Jan 13, 2021 10:43 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Why is the concentration of Ba2+ the same as barium hydroxide?
- Replies: 7
- Views: 434
Re: Why is the concentration of Ba2+ the same as barium hydroxide?
1 molecule of Ba(OH)2 has one atom on Barium, meaning that the ratio of their stoichiometric coefficients is 1:1. Because of this, the concentration of Ba2+ and Ba(OH)2 should be equal.
- Wed Jan 13, 2021 10:39 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Ka and Weak Acids
- Replies: 3
- Views: 129
Re: Ka and Weak Acids
A larger Ka value means a stronger acid. This is because Ka is calculated by dividing the concentration of products by the concentration of reactants generally speaking. A acid's strength is determined by how much of it dissociates in water, so a stronger acid should produce more products, increasin...
- Wed Jan 13, 2021 10:27 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Dilute Solution
- Replies: 4
- Views: 120
Re: Dilute Solution
I agree. For this class, we can assume the dilution solvent to be water (unless stated otherwise).
- Wed Jan 06, 2021 8:30 pm
- Forum: Ideal Gases
- Topic: Sapling Homework
- Replies: 22
- Views: 858
Re: Sapling Homework
305538876 wrote:Re: Sapling Homework
Try emailing the ucla store (textonline@asucla.ucla.edu) and ask them to send you the code. Last quarter my sapling code never arrived physically, but I was able to get the code by emailing them!
- Wed Jan 06, 2021 7:40 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Homogeneous & Heterogeneous Reactions
- Replies: 4
- Views: 304
Re: Homogeneous & Heterogeneous Reactions
For heterogeneous reactions it's important to exclude any solids or liquids in the reaction when calculating for K since their concentration remains constant. For homogeneous reactions you use all the reactants and products when calculating for K.
- Wed Jan 06, 2021 7:30 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Sapling Homework
- Replies: 6
- Views: 272
Re: Sapling Homework
Yup the only homework problems we have to submit are the ones from Sapling, although we also have the 5 discussion posts per week requirement. We get unlimited tries which is really nice. The problems listed in the syllabus are completely optional, but they're quite helpful when trying to master the...
- Wed Jan 06, 2021 7:21 pm
- Forum: Ideal Gases
- Topic: Temperature in Ideal Gas Law
- Replies: 14
- Views: 309
Re: Temperature in Ideal Gas Law
For Ideal Gas Law, we should use Kelvin. Since pressure and volume can't be negative, the value plugged in for temperature must also never be negative so that the two sides of the equation can be equal. Because Kelvin can't go below zero, we use it as opposed to Fahrenheit or Celsius.
- Wed Jan 06, 2021 7:11 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: dobule arrows
- Replies: 6
- Views: 200
Re: dobule arrows
I agree that it most likely means much less than. For example going back to VSPER, trigonal pyramid has a bond angle x < 109.5, while bent (2BP,2LP) had a bond angle x << 109.5 since it usually had a smaller bond angle than molecules with the trigonal planar shape.
- Tue Dec 08, 2020 11:45 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: calculating pH using sig figs
- Replies: 3
- Views: 179
Re: calculating pH using sig figs
It's probably best to not round in this case just to make sure the answer is accurate. They'll probably make it clear which way they want us to round (up or down) on the final if they really do want us to follow sigfigs.
- Tue Dec 08, 2020 11:36 pm
- Forum: Bond Lengths & Energies
- Topic: Compound stability
- Replies: 5
- Views: 320
Re: Compound stability
I would first look at intermolecular forces. If they're of the same type, then examine the bond length.
- Tue Dec 08, 2020 11:23 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: tetrahedral vs octahedral correction lec 24
- Replies: 2
- Views: 65
Re: tetrahedral vs octahedral correction lec 24
Yup, he probably meant tetrahedral since octahedral has 6 bonds
- Tue Dec 08, 2020 11:20 pm
- Forum: Naming
- Topic: coordination compounds with aqua
- Replies: 12
- Views: 625
Re: coordination compounds with aqua
I personally prefer using OH2 since it makes clear that oxygen is the element that's bonded, but either one is valid!
- Tue Dec 08, 2020 11:17 pm
- Forum: Naming
- Topic: Naming quizlet
- Replies: 41
- Views: 1607
Re: Naming quizlet
Thank you so much! I really appreciate it!
- Sun Dec 06, 2020 2:03 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Memorizing shapes based on general formula?
- Replies: 5
- Views: 408
Re: Memorizing shapes based on general formula?
Yup, I think it's a good idea to memorize the shapes and the corresponding number of bonded pairs and lone pairs they each have. It's probably also helpful to memorize their corresponding bond angles.
- Sun Dec 06, 2020 1:48 pm
- Forum: Dipole Moments
- Topic: Dipole canceling
- Replies: 13
- Views: 633
Re: Dipole canceling
Yup! Nonpolar molecules can have polar bonds. As long as the differences in electronegativity cancels out, it's considered nonpolar. This is common in molecules that have the VSPER shape of linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral, and square planer when the surrounding...
- Sun Dec 06, 2020 1:39 pm
- Forum: Lewis Structures
- Topic: Angles of Bonding Pairs
- Replies: 8
- Views: 418
Re: Angles of Bonding Pairs
I think we'll have to know the bond angles for molecules with the VSPER shape of linear, trigonal planar, tetrahedral, trigonal bipyrimidal, square planar, and octahedral. However for molecules with other shapes, we probably aren't expected to know the exact bond angle. For example, for the water mo...
- Sun Dec 06, 2020 1:18 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Flashcards
- Replies: 8
- Views: 252
Re: Flashcards
Yup, flashcards are definitely helpful, especially since the naming rules require hard memorization at first. Doing multiple practice problems from the book and online is really useful too.
- Sun Dec 06, 2020 1:14 pm
- Forum: Naming
- Topic: Naming Practice
- Replies: 4
- Views: 314
Re: Naming Practice
Thanks so much! I really needed some practice
- Sun Nov 29, 2020 8:28 pm
- Forum: Significant Figures
- Topic: 40. versus 40
- Replies: 23
- Views: 1449
Re: 40. versus 40
Yup! Zeroes at the end of a digit (trailing zeros) are only significant if there is a decimal point present.
- Fri Nov 27, 2020 11:15 pm
- Forum: SI Units, Unit Conversions
- Topic: How to memorize prefixes
- Replies: 36
- Views: 3314
Re: How to memorize prefixes
As others have said quizlet/flashcards are pretty helpful when trying to memorize the prefixes. Unit conversion problems help out a lot too. Good luck!
- Fri Nov 27, 2020 11:07 pm
- Forum: Biological Examples
- Topic: Hemoglobin
- Replies: 13
- Views: 708
Re: Hemoglobin
Just to add on, although both transport oxygen, hemoglobin can bind to more oxygen molecules at a time. I believe hemoglobin can bind to 4 oxygen molecules while myoglobin can only bind to 1 oxygen molecule at a time.
- Fri Nov 27, 2020 11:03 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Ring Structures
- Replies: 9
- Views: 248
Re: Ring Structures
There's definitely a possibility it could show up on the final since there's been so many examples given in class and in sapling. Hopefully they'll given us a clue on the test if they do want us to draw a ring structure.
- Fri Nov 27, 2020 10:51 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Shape Sheet
- Replies: 7
- Views: 655
Re: Shape Sheet
I like using this one! Hope it helps!
https://s3-us-west-2.amazonaws.com/courses-images/wp-content/uploads/sites/752/2016/09/26194726/vsepr-geometries.png
https://s3-us-west-2.amazonaws.com/courses-images/wp-content/uploads/sites/752/2016/09/26194726/vsepr-geometries.png
- Fri Nov 27, 2020 10:44 pm
- Forum: Naming
- Topic: Naming Complexes
- Replies: 7
- Views: 188
Re: Naming Complexes
I agree! He'll most likely go over it in depth during next week's lectures. He's just finishing up the basics for now.
- Sat Nov 21, 2020 9:56 pm
- Forum: Lewis Structures
- Topic: Central Atom Question
- Replies: 20
- Views: 1071
Re: Central Atom Question
Since H can only form one single bond, it's never the central atom. As a rule of thumb, the element with the lowest ionization energy is often the central atom.
- Sat Nov 21, 2020 9:46 pm
- Forum: Dipole Moments
- Topic: higher dipole moment sapling #10
- Replies: 5
- Views: 1143
Re: higher dipole moment sapling #10
As said above, the two fluorines in COF2 cancel each other out somewhat. Oxygen is very electronegative as well, so overall the polarity in COF2 isn't as strong (relatively speaking). In comparison, the hydrogen in COHF is much less electronegative than the oxygen or fluorine, leading to the dipoles...
- Sat Nov 21, 2020 9:31 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Best Formal Charge Equations
- Replies: 24
- Views: 990
Re: Best Formal Charge Equations
I like using the FC = # of VE - # of dots - # of lines equation as well! I find it to the the fastest method once the lewis structure is drawn out.
- Sat Nov 21, 2020 9:23 pm
- Forum: Hybridization
- Topic: Resonance Structures and Sigma & Pi Bonds
- Replies: 6
- Views: 429
Re: Resonance Structures and Sigma & Pi Bonds
Yup! Resonance structures have sigma and pi bonds. I believe the pi bonds in resonance structures are specifically called delocalized pi bonds.
- Sat Nov 21, 2020 9:20 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: double bonding
- Replies: 8
- Views: 488
Re: double bonding
For VSPER, the molecular shape is dependent on the number of lone pairs and bonded pairs surrounding the central atom, more so than whether the bonds are single bonds or double bonds. I believe this is because the type of bond affects the bond length and strength but not the amount of repulsion it f...
- Thu Nov 12, 2020 3:21 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Memorizing Formula
- Replies: 4
- Views: 328
Re: Memorizing Formula
A trick I like to use is to look at the Lewis structure and count the number of lines and dots surrounding an atom. Since each line represents a bonding pair of electrons, we can count the number of shared electrons/2 by counting the number of lines surrounding the element. Similarly, since each dot...
- Thu Nov 12, 2020 3:03 pm
- Forum: Ionic & Covalent Bonds
- Topic: Ions
- Replies: 6
- Views: 148
Re: Ions
I don't think we're required to, but it is useful to have the most common ones memorized. Here's a list of the most common polyatomic ions!
https://ch301.cm.utexas.edu/help/ch301/polyatomics.pdf
https://ch301.cm.utexas.edu/help/ch301/polyatomics.pdf
- Thu Nov 12, 2020 2:57 pm
- Forum: Dipole Moments
- Topic: Polar covalent bonds
- Replies: 5
- Views: 186
Re: Polar covalent bonds
Dipole - dipole force happens between two polar molecules, making it an intermolecular force. Polar covalent bonds form between 2 atoms with different electronegativities , making it an intramolecular force. A molecule that is considered polar can experience dipole dipole with another polar molecule.
- Tue Nov 10, 2020 8:15 pm
- Forum: Lewis Structures
- Topic: Resonance and Formal Charge
- Replies: 3
- Views: 205
Re: Resonance and Formal Charge
If two structures have the same overall formal charge, then examine the location of the elements' individual formal charge. Theoretically, elements with higher electronegativity should have a negative formal charge since they're drawing in more electrons, so it's most likely the structure that follo...
- Tue Nov 10, 2020 8:02 pm
- Forum: Dipole Moments
- Topic: London Dispersion forces
- Replies: 7
- Views: 177
Re: London Dispersion forces
There aren't any exceptions as far as I know. I believe molecules/salts with larger molar mass and larger surface areas have bigger London Dispersion forces.
- Sun Nov 08, 2020 1:21 pm
- Forum: Lewis Structures
- Topic: lewis structure
- Replies: 10
- Views: 353
Re: lewis structure
Formal Charge = # of valence electrons - (shared electrons/2 + lone pairs). A short cut to this if you have the lewis structure drawn out is FC = VE - (number of lines + number of dots) since the lines represent the bonded electrons and the dots represent the lone electrons.
- Sun Nov 08, 2020 12:57 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Formal Charge of the Same Element
- Replies: 15
- Views: 403
Re: Formal Charge of the Same Element
The formal charge of an element can vary, even within the same molecule. A great example of this is resonance structures, such as nitrite (NO2^-). In the lewis structure of nitrite, one of the oxygen has 3 lone pairs and a single bond with nitrogen, giving it a formal charge of -1. The other oxygen ...
- Sun Nov 08, 2020 12:47 pm
- Forum: Electronegativity
- Topic: Lewis Acids and Bases (Sapling #6)
- Replies: 4
- Views: 256
Re: Lewis Acids and Bases (Sapling #6)
Lewis acids accepts electron pairs. They're more likely to have a positive charge. The central atom in Lewis acids tend to have no lone pairs. Lewis bases donate electron pairs. They tend to have a negative charge. The central atom in Lewis bases tend to have lone pairs that are donated to Lewis aci...
- Sun Nov 08, 2020 12:35 pm
- Forum: Resonance Structures
- Topic: Rules for Determining Favored Structure
- Replies: 8
- Views: 510
Re: Rules for Determining Favored Structure
The favored resonance structure should have the lowest formal charge. If two resonance structures have the same formal charge, choose the structure where the negative formal charge is on the more electronegative element.
- Sun Nov 08, 2020 12:24 pm
- Forum: Resonance Structures
- Topic: Oxidation Number
- Replies: 9
- Views: 271
Re: Oxidation Number
To add on, for polyatomic ions, the sum of oxidation numbers should equal the charge of the ion. For example, in sulfate (SO4^2-), we know that the sum of the oxidation numbers should equal -2 and that the oxidation number for O is -2. We can get the equation X +4(-2) = -2 where X equals the oxidati...
- Sun Nov 01, 2020 4:17 pm
- Forum: Ionic & Covalent Bonds
- Topic: Covalent Bonds
- Replies: 9
- Views: 304
Re: Covalent Bonds
Within the context of this class, covalent bonds are generally stronger than ionic bonds, but it can depend on the environment. For example, within a solution, ionic bonds are weaker than covalent bonds. Since many of the chemical reactions in biology involve solutions, we consider covalent bonds to...
- Sun Nov 01, 2020 3:44 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Sapling HW Q17
- Replies: 18
- Views: 1210
Re: Sapling HW Q17
As you go across a period, atomic radius decreases since effective nuclear charge increases. The increased attraction between the protons and electrons leads to the electrons being drawn in closer to the nucleus, decreasing atomic radius. As you go down a group, atomic radius increases due to the in...
- Sun Nov 01, 2020 3:30 pm
- Forum: Trends in The Periodic Table
- Topic: Atomic Radius
- Replies: 30
- Views: 2852
Re: Atomic Radius
Atomic radius decreases as you go across a period due to increasing nuclear charge. The stronger nuclear charge leads to an increased attraction between the positively charged protons in the nucleus and negatively charged electrons surrounding it. This leads to the electrons, including the valence e...
- Sun Nov 01, 2020 3:20 pm
- Forum: Trends in The Periodic Table
- Topic: Oxygen and Ionization Energy
- Replies: 9
- Views: 501
Re: Oxygen and Ionization Energy
I believe oxygen has a lower ionization energy compared to nitrogen due to increased electron electron repulsion within the orbital. For nitrogen, there's 1 electron in the 3 orbitals of the 2 p subshell. However, in oxygen there's suddenly 2 electrons in one of the orbitals, which increases electro...
- Sun Nov 01, 2020 2:57 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Orbital vs. Subshell
- Replies: 13
- Views: 735
Re: Orbital vs. Subshell
Each subshell has 1 or more or orbitals. Within an orbital, there's a high probability that an electron can be found. Also depending on the type of subshell, the number and shape of orbitals changes. (s subshells have 1 orbital, p subshells have 3 orbitals, d subshells have 5 orbitals, and f subshel...
- Thu Oct 22, 2020 10:25 pm
- Forum: SI Units, Unit Conversions
- Topic: SI Conversions
- Replies: 11
- Views: 322
Re: SI Conversions
To be on the safe side, it's probably best to memorize the more common conversions. One trick is to memorize the prefixes! (ex. kilo detonates 1000x, so 1 km = 1000m and 1 kg = 1000g). There's also angstrom, which represents 10^-10.
- Thu Oct 22, 2020 10:14 pm
- Forum: Significant Figures
- Topic: Midterm
- Replies: 9
- Views: 473
Re: Midterm
Not 100% sure, but even if there isn't a question dedicated to it, I imagine that we could get points docked off if our answers don't have the correct number of sig figs.
- Thu Oct 22, 2020 10:04 pm
- Forum: Limiting Reactant Calculations
- Topic: General Limiting Question
- Replies: 9
- Views: 782
Re: General Limiting Question
Yup, since the limiting reactant will run out first, it determines how much product will be created. It's possible that less product will form than expected in an actual experiment though due to factors such as the reactants sticking to the side of the tubes and not properly reacting.
- Thu Oct 22, 2020 9:56 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Advice for studying
- Replies: 92
- Views: 6223
Re: Advice for studying
I find the questions from the textbook and the step-up sessions very useful! I would also recommend writing down all the important formulas on a piece of paper and the memorizing and understanding the formulas. I think we will be given a formula sheet (maybe?), but flipping back and forth between pa...
- Thu Oct 22, 2020 9:46 pm
- Forum: Student Social/Study Group
- Topic: Midterm Fundamentals Review Sheet
- Replies: 7
- Views: 353
Re: Midterm Fundamentals Review Sheet
This looks super helpful! Thank you so much!! (Side note but your handwriting is so nice ;-;)
- Sun Oct 18, 2020 7:39 pm
- Forum: Properties of Light
- Topic: energy level transfer
- Replies: 7
- Views: 152
Re: energy level transfer
I think based off the equation E=-(hR)/n^2, E and n have an inverse relationship (As n increases, E will decrease. As n decreases, E will increase). So as n gets larger and larger and eventually approaches infinity, E will get smaller and smaller to the point where it is so minuscule, that it's appr...
- Sun Oct 18, 2020 7:26 pm
- Forum: Photoelectric Effect
- Topic: Light Intensity
- Replies: 23
- Views: 403
Re: Light Intensity
Yup! The number of photons increases when the brightness increases, but the wavelength/frequency of each photon remains the same. If the wavelength/frequency changed, then that could've changed what type of EM wave it was instead (ex. from visible light to UV light if the frequency increased/wavelen...
- Sun Oct 18, 2020 7:12 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Midterm Exam Format
- Replies: 14
- Views: 493
Re: Midterm Exam Format
Yes, all multiple choice. According to my TA, they're going to try to give partial credit, but I'm not exactly sure how.
- Sun Oct 18, 2020 7:08 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Built-in webcams/Equipment request [ENDORSED]
- Replies: 22
- Views: 1403
Re: Built-in webcams/Equipment request [ENDORSED]
I think it could depend on your TA. Mine is allowing us to use our phone or tablet as an external camera.
- Sun Oct 18, 2020 7:04 pm
- Forum: Administrative Questions and Class Announcements
- Topic: UCLA Store Updates on Ebook/Sapling access card
- Replies: 16
- Views: 600
Re: UCLA Store Updates on Ebook/Sapling access card
I placed my order around the end of week 0, and I still haven't received it in the mail. According to the store, my order has been shipped though, so I hope it'll arrive soon. I'll probably email them soon for a code.
- Mon Oct 05, 2020 8:49 pm
- Forum: Balancing Chemical Reactions
- Topic: Stoichiometric Coefficients
- Replies: 20
- Views: 409
Re: Stoichiometric Coefficients
I would say it's best to check because better safe than sorry! I've had so many instances where I forgot to check in the beginning and had to redo all the calculations. It ends up saving lots of time in the long run!
- Mon Oct 05, 2020 8:38 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: Mol VS Mole
- Replies: 17
- Views: 680
Re: Mol VS Mole
Yup, mol is just a shorthand for mole! Unfortunately mol almost looks like an abbreviation for molecule (which I've seen abbreviated as mlcl before).
- Mon Oct 05, 2020 8:22 pm
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: Determining Molar Mass
- Replies: 19
- Views: 583
Re: Determining Molar Mass
It probably wouldn't make a significant difference in most cases, but if you want to be on the safe side use 15.999.
- Mon Oct 05, 2020 8:10 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Advice from a Medical Student [ENDORSED]
- Replies: 297
- Views: 374247
Re: Advice from a Medical Student [ENDORSED]
Thank you so much for your advice! I'll try to take more notes during lecture from now on!