Search found 35 matches

by Leslie Cheng 4B
Sat Dec 08, 2018 1:33 pm
Forum: Conjugate Acids & Bases
Topic: strength of conjugate acids & bases
Replies: 1
Views: 115

strength of conjugate acids & bases

If you have a strong base, is the conjugate acid always going to be weak? Can you ever have a weak base make a weak conjugate acid?
by Leslie Cheng 4B
Fri Dec 07, 2018 10:15 pm
Forum: Administrative Questions and Class Announcements
Topic: FINAL PRACTICE - Lyndon's Churro Review Session [ENDORSED]
Replies: 118
Views: 4949

Re: FINAL PRACTICE - Lyndon's Churro Review Session [ENDORSED]

On question 21, can someone explain why Fe has an oxidation state of +2? I get that this is because of the nitrogens, but how do the nitrogens come to have a charge of -2? I was trying to calculate the formal charge but kept getting a positive charge on the nitrogens, not a negative charge.
by Leslie Cheng 4B
Thu Dec 06, 2018 12:57 pm
Forum: Calculating the pH of Salt Solutions
Topic: how to determine pH of salt solutions easily
Replies: 1
Views: 159

how to determine pH of salt solutions easily

Does anyone have a method they use to determine the pH of salt solutions easily? Do you just look at the salt, split it up into its constituent parts, then see whether the cation or anion affects the pH of the solution? What's your mechanism for solving these types of problems?
by Leslie Cheng 4B
Wed Dec 05, 2018 10:03 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: ion-ion interactions
Replies: 1
Views: 170

ion-ion interactions

What's the difference between an ion-ion interaction and an ionic bond? Is one stronger than the other?
by Leslie Cheng 4B
Wed Dec 05, 2018 9:41 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Determining possible intermolecular forces
Replies: 3
Views: 84

Determining possible intermolecular forces

Is there an easy way to remember which type of intermolecular forces are possible by looking at a molecule? What are the key characteristics of each type of intermolecular force? (For example, dispersion forces are present in all molecules?)
by Leslie Cheng 4B
Tue Nov 27, 2018 8:27 pm
Forum: Dipole Moments
Topic: Nonpolar and Dipole Moments?
Replies: 3
Views: 63

Re: Nonpolar and Dipole Moments?

Oh yeah, a molecule can still be classified as nonpolar even if it has polar bonds. The dipole moments on that molecule just need to cancel out, which is why symmetrical molecules are usually nonpolar.
by Leslie Cheng 4B
Tue Nov 27, 2018 8:25 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: dipole-induced dipole
Replies: 1
Views: 55

Re: dipole-induced dipole

You could have water and an oxygen molecule. Water is a polar molecule with a permanent dipole moment, so it has partial charges. The oxygen atom in water is delta negative whereas the hydrogen atoms in water are delta positive. The partial charges on this water molecule induces, or causes, a dipole...
by Leslie Cheng 4B
Tue Nov 27, 2018 8:21 pm
Forum: Dipole Moments
Topic: Nonpolar and Dipole Moments?
Replies: 3
Views: 63

Re: Nonpolar and Dipole Moments?

Well, electric dipole moment and dipole moment basically mean the same thing. In nonpolar molecules, instantaneous dipole moments can occur due to random fluctuations in the electron density of the originally nonpolar molecule. If you're asking about permanent dipole moments, then no, the very defin...
by Leslie Cheng 4B
Tue Nov 27, 2018 8:17 pm
Forum: Hybridization
Topic: Hybridization/VSEPR
Replies: 1
Views: 54

Re: Hybridization/VSEPR

I'm pretty sure you just have to be able to figure out the hybridization based on how many regions of electron density there are around the atom in question. If there are three regions of electron density, for example, it'd be sp^2. If there are four regions of electron density, it'd be sp^3, and so...
by Leslie Cheng 4B
Tue Nov 27, 2018 8:14 pm
Forum: General Science Questions
Topic: how to draw a double bond that is coming at you
Replies: 6
Views: 204

Re: how to draw a double bond that is coming at you

I don't think you need to know that for this course, because we've never had a situation where we had to do that?
by Leslie Cheng 4B
Tue Nov 27, 2018 8:12 pm
Forum: Dipole Moments
Topic: Dipole-Dipole
Replies: 3
Views: 77

Re: Dipole-Dipole

Well, a dipole-dipole interaction is a type of intermolecular interaction, which means it's going to be between two molecules. You could look at a lewis structure and see if it's polar (usually polar molecules are asymmetrical and have dipole moments that don't cancel) because polar molecules have p...
by Leslie Cheng 4B
Mon Nov 19, 2018 12:26 pm
Forum: Bond Lengths & Energies
Topic: Polarity of different bond lengths
Replies: 3
Views: 83

Polarity of different bond lengths

Does the multiplicity of bonds affect the polarity of a bond at all? For example, if you had a single polar bond between two elements, would a double bond between the same two elements make the bond more polar than it originally was?
by Leslie Cheng 4B
Wed Nov 14, 2018 10:03 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: homework 2E #11 part b
Replies: 2
Views: 45

homework 2E #11 part b

On the homework for Focus 2E #11 part b, the book asks you to predict the shape of iodine trichloride. Why is the molecule t-shaped instead of trigonal? I thought lone pair-lone pair repulsion is the strongest, and therefore the lone pairs would want to be the furthest away from each other and 180 d...
by Leslie Cheng 4B
Wed Nov 14, 2018 9:55 pm
Forum: Ionic & Covalent Bonds
Topic: general question about polarity of bonds
Replies: 1
Views: 64

general question about polarity of bonds

I'm not sure if this is the right section to post in, but I was wondering if the multiplicity of bonds affects polarity? For example, would a double bond between two elements have a different polarity than a single bond between the same two elements?
by Leslie Cheng 4B
Tue Nov 13, 2018 10:29 pm
Forum: Lewis Structures
Topic: Homework 2.25
Replies: 2
Views: 84

Homework 2.25

On problem 2.25 part b, it asks whether the NF bond in NF3 or the PF bond in PF3 is longer. Since both Lewis structures are pretty much the same besides the central atom, is the PF bond in PF3 longer than the NF bond because P is less electronegative than N, and therefore pulls in the shared electro...
by Leslie Cheng 4B
Wed Nov 07, 2018 12:41 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 903635

Re: Post All Chemistry Jokes Here

"Did you lose an electron? I'm going to keep ion on it"

Cation: noun
an atom with a paw-sitive charge!
by Leslie Cheng 4B
Wed Nov 07, 2018 12:37 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Polarizing power/polarizability periodic trends
Replies: 2
Views: 101

Polarizing power/polarizability periodic trends

Can someone explain to me what the periodic trends of the polarizing power of cations and the polarizability of anions are? I believe the textbook mentioned that cations increase in polarizing power across a period left to right, for example. Why is this so?
by Leslie Cheng 4B
Wed Nov 07, 2018 12:35 pm
Forum: Octet Exceptions
Topic: Octet Exceptions
Replies: 4
Views: 94

Re: Octet Exceptions

I just remember three octet exceptions: 1) expanded valence shells-any element in period 3 or above can accommodate more than an octet because its electrons can go into its d-orbitals 2) incomplete octets-elements in group 13 like Boron will have an odd number of electrons so they won't get an octet...
by Leslie Cheng 4B
Wed Oct 31, 2018 10:16 pm
Forum: Ionic & Covalent Bonds
Topic: octet rule
Replies: 11
Views: 201

Re: octet rule

It's also good to note that the idea of filling octets is simply a guideline, not a rule. In the case of expanded valence shells like in the case of P, Cl, or S, these elements are able to have bonds that go beyond what an octet would allow.
by Leslie Cheng 4B
Wed Oct 31, 2018 10:10 pm
Forum: Resonance Structures
Topic: 2C.3 on homework
Replies: 1
Views: 97

2C.3 on homework

Question 2C.3 in the seventh edition asks to draw the Lewis structure, including typical contributions to the resonance structure (where appropriate, allow for the possibility of octet expansion, including double bonds in different positions). Then it gives a) periodate ion; b) hydrogen phosphate io...
by Leslie Cheng 4B
Wed Oct 31, 2018 11:01 am
Forum: Resonance Structures
Topic: General guideline for drawing structures
Replies: 4
Views: 148

General guideline for drawing structures

Hi! Does anyone have a general guideline for drawing lewis or resonance structures? For example, I'm not sure if I should calculate the formal charge for all possible structures first before deciding on which structure is the correct one, because it seems a bit time-consuming during timed tests. Tha...
by Leslie Cheng 4B
Fri Oct 26, 2018 7:12 pm
Forum: Trends in The Periodic Table
Topic: electron affinity 1F.11
Replies: 3
Views: 117

electron affinity 1F.11

Question 1F.11 asks you to pick which element within each pair has the higher electron affinity: a) tellurium or iodine, b) beryllium or magnesium, c) oxygen or sulfur, d) gallium or indium. I know that electron affinity is highest to the right of the periodic table because those elements (groups 16...
by Leslie Cheng 4B
Wed Oct 24, 2018 8:55 pm
Forum: Student Social/Study Group
Topic: ChemCommunity posting
Replies: 4
Views: 206

Re: ChemCommunity posting

According to my TA, the deadline every week is Sunday, but I'd check with your TA to see if they have different policies :)
by Leslie Cheng 4B
Tue Oct 23, 2018 10:07 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: exceptions: chromium & copper
Replies: 2
Views: 60

exceptions: chromium & copper

In class, Dr. Lavelle talked about how chromium and copper are the two exceptions to electron configuration we should know. If chromium is [Ar] 3d^5 4s^1 and copper is [Ar] 3d^10 4s^1, does that mean in these elements, the 4s orbital is lower than the 3d orbital since the 4s state is not completely ...
by Leslie Cheng 4B
Mon Oct 22, 2018 8:10 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: orbitals and wave functions
Replies: 2
Views: 70

orbitals and wave functions

In class, Dr. Lavelle reiterated that electrons in orbitals are in "states", and that they're not actually orbiting. Can someone explain to me the relationship between wave functions and orbitals? Are the two terms interchangeable? Where does the whole using math functions to model electro...
by Leslie Cheng 4B
Thu Oct 18, 2018 3:50 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Quantum numbers, shells, subshells
Replies: 2
Views: 43

Quantum numbers, shells, subshells

I was reading section 1D.3 in the textbook about quantum numbers, shells, and subshells, and I'm confused about how all of these are linked together. Can someone explain to me what the letters (n,l,m) mean in this context and also how to remember how many orbitals there are in each shell/subshell? J...
by Leslie Cheng 4B
Thu Oct 18, 2018 3:43 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Nodal Planes
Replies: 1
Views: 30

Re: Nodal Planes

You know that there are four types of orbitals: s, p, d, and f. S orbitals are spheres and therefore have no nodal planes. P orbitals look like figure eights and have one nodal plane. D orbitals have two nodal planes, and F orbitals have 3. The most important thing to remember is that S orbitals hav...
by Leslie Cheng 4B
Wed Oct 17, 2018 10:37 am
Forum: Quantum Numbers and The H-Atom
Topic: Lyman, Balmer, Pascal
Replies: 10
Views: 325

Re: Lyman, Balmer, Pascal

Recall that for the hydrogen emission/absorption spectrum, we see a spectral line when an electron moves from a higher to a lower energy level. The Lyman, Balmer, and Paschen series simply refer to specific groups of spectral lines. The Lyman series starts with energy level n=1, the Balmer series st...
by Leslie Cheng 4B
Sat Oct 13, 2018 1:30 pm
Forum: Properties of Electrons
Topic: Atomic Spectra: Balmer & Lyman Series (energy levels)
Replies: 2
Views: 58

Re: Atomic Spectra: Balmer & Lyman Series (energy levels)

Yes, I believe so. The textbook even says that for the Lyman series n1 is always 1, and n2 is 2,3, etc, whereas for the Balmer series n1 is always 2, and n2 is 3,4,etc. I think the method Dr. Lavelle outlined in lecture, calculating each individual energy level using the equation En = -hR/n^2, then ...
by Leslie Cheng 4B
Wed Oct 10, 2018 8:51 pm
Forum: Einstein Equation
Topic: Work Function
Replies: 4
Views: 80

Re: Work Function

If you recall the photoelectric effect experiment with shining light on different metals to try to remove electrons from it, those electrons require energy to eject. This minimum energy needed to remove electrons from the surface of that metal is the threshold energy, represented by the work functio...
by Leslie Cheng 4B
Wed Oct 10, 2018 8:41 pm
Forum: Properties of Light
Topic: Light acts as a wave or not?
Replies: 10
Views: 137

Re: Light acts as a wave or not?

We do not know exactly what light looks like, so we can only come up with models of it. We have the wave model and the particle model. The particle model was only conceived of when the photoelectric effect was discovered. Therefore, light has qualities of both the wave and particle models, but it al...
by Leslie Cheng 4B
Thu Oct 04, 2018 11:55 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: diatomic elements
Replies: 12
Views: 603

diatomic elements

Hi! Can someone explain to me why diatomic elements form, and how to distinguish between whether an element is existing in its diatomic form or not? For example, if a problem involves a diatomic element like oxygen, do you assume that's in a diatomic form, or does the problem have to state explicitl...
by Leslie Cheng 4B
Wed Oct 03, 2018 10:21 pm
Forum: Limiting Reactant Calculations
Topic: Fundamental M.9 [ENDORSED]
Replies: 3
Views: 99

Fundamental M.9 [ENDORSED]

Hi, this problem states that copper (II) nitrate reacts with sodium hydroxide to produce a precipitate of light blue copper (II) hydroxide. It asks you to write the net ionic equation for the reaction. What does net ionic equation mean?
by Leslie Cheng 4B
Tue Oct 02, 2018 8:25 pm
Forum: Empirical & Molecular Formulas
Topic: Fundamental L.39
Replies: 6
Views: 111

Fundamental L.39

Hi! The problem says that you have a 1.50g sample on tin placed in a 26.45g crucible that is heated until the tin reacts to the oxygen in the air to form and oxide. The product and the crucible together weigh 28.35g. How do you figure out the empirical formula of the oxide, and how do you name it? A...
by Leslie Cheng 4B
Tue Oct 02, 2018 8:08 pm
Forum: Balancing Chemical Reactions
Topic: Problem L.35
Replies: 5
Views: 80

Re: Problem L.35

I have the seventh edition too but no solutions manual...I definitely did not think about it being a typo and thought I was just horrible at balancing equations. Thank you all for catching that :)

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