Search found 53 matches

Thu Dec 05, 2019 7:32 am
Forum: Calculating the pH of Salt Solutions
Topic: Equilibrium Tables
Replies: 1
Views: 43

Equilibrium Tables

Will we have to know how to solve questions using equilibrium tables (example 6D4 in the textbook)? I just wanted to check since Dr. Lavelle didn't cover these types of questions during the lecture. Thank you so much!
Wed Dec 04, 2019 9:18 am
Forum: Coordinate Covalent Bonds
Topic: When do we use the prefixes bis, tris, tetrakis, etc?
Replies: 4
Views: 156

Re: When do we use the prefixes bis, tris, tetrakis, etc?

di- and tri- are used when there are more than one of the same ligand attached to the central metal ion. bis-, tris- and tetrakis- are used to signify the presence of more than one polydentate ligand. For instance, if you have two oxalato ligands in a coordination compound, it would be written as -b...
Wed Dec 04, 2019 9:14 am
Forum: Sigma & Pi Bonds
Topic: finding hybridizations
Replies: 2
Views: 109

Re: finding hybridizations

I believe the integer in front of the hybridization signifies the principal energy level n at which the hybrid bond is formed. E.g. n= 2 for 2sp^3
Hope this helps!
Wed Dec 04, 2019 9:11 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: pK
Replies: 2
Views: 39

Re: pK

1. Whenever a "p" is placed before the letter (e.g. pKa or pKb), it signifies that you have to take the -log of the corresponding value (pKa = -logKa, pKb = -logKb, pKw = -logKw). 2. Ka is the acid dissociation constant and measures the extent to which an acid breaks down into its componen...
Wed Dec 04, 2019 9:01 am
Forum: Bronsted Acids & Bases
Topic: CaO
Replies: 10
Views: 126

Re: CaO

I believe the -OH and -O bases formed from alkali and alkaline earth metals are typically classified as strong bases. Hope this helps!
Sun Dec 01, 2019 2:08 pm
Forum: Naming
Topic: Water in Coordination Compounds
Replies: 7
Views: 98

Water in Coordination Compounds

When I was looking through the solution manual, I noticed that water was often written as OH2 instead of H2O in the formulas of coordination compounds. Can someone explain why this is the case? Will we be penalized on an exam if we write it one way as opposed to the other? Thank you so much!
Sun Dec 01, 2019 2:00 pm
Forum: Biological Examples
Topic: Coordination Compounds and Chemotherapy Drugs
Replies: 5
Views: 77

Re: Coordination Compounds and Chemotherapy Drugs

Does anyone know what information we have to specifically know about these chemotherapy drugs? Is it just that they're an example of a coordination compound? I was absent during this lecture, so I'd appreciate any information! Thank you so much :)
Sun Dec 01, 2019 1:53 pm
Forum: Sigma & Pi Bonds
Topic: Drawing Sigma and Pi bonds
Replies: 7
Views: 110

Re: Drawing Sigma and Pi bonds

I think you have to label each bond individually for double/triple bonds (e.g. write pi above one of the double bonds and sigma above the other). However, the order with which you label pi/sigma for multiple bonds does not matter as long as you have the correct number of each type of bond. And yes, ...
Sun Dec 01, 2019 1:50 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: pKa
Replies: 4
Views: 51

Re: pKa

The pKa value is one method that is utilized to indicate the strength of an acid. It is calculated by taking the negative of the log base 10 of the acid dissociation constant, Ka (thus the p before the Ka). As the acid dissociation constant Ka increases, pKa decreases. Thus lower values of pKa are a...
Sun Dec 01, 2019 1:40 pm
Forum: Bronsted Acids & Bases
Topic: Net Ionic Equations
Replies: 3
Views: 65

Re: Net Ionic Equations

I believe it depends on whether an acid is strong or weak. Strong acids (e.g. HCl, HBr) are completely disassociated in solution, so they are written as a sum of their ionic components. However, weak acids (e.g. HF) typically retain their identity/not disassociate, so they are not broken into their ...
Sun Nov 24, 2019 2:56 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 2
Views: 56

Re: Bond Angles

Here are the different molecular shapes and their bond angles as defined by VSEPR theory: (2 regions of electron density) Linear: 180 degrees (3 regions of electron density) Trigonal Planar: 120 degrees, Bent: <120 degrees (4 regions of electron density) Tetrahedral: 109.5 degrees, Trigonal Pyramida...
Sun Nov 24, 2019 2:47 pm
Forum: Hybridization
Topic: d-orbitals
Replies: 7
Views: 89

Re: d-orbitals

Yes! D-orbitals are often involved in hybridization in elements belonging to Period 3 or later because they can accommodate five or more electron pairs. As a result of the expanded valence shell, they require d-orbitals in their hybridized orbitals to account for all of the regions of electron densi...
Sun Nov 24, 2019 2:39 pm
Forum: Administrative Questions and Class Announcements
Topic: Difficulty
Replies: 14
Views: 198

Re: Difficulty

I think the difficulty of this class depends on your prior experience with chemistry. If you took AP chemistry in high school, I would tend to believe that many of the concepts in 14A are a review. Personally, this class is moderately challenging for me because I only took an honors chem class in hi...
Sun Nov 24, 2019 2:36 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Non-polar atoms with lone pairs
Replies: 4
Views: 41

Re: Non-polar atoms with lone pairs

I have a follow-up question: How can we tell that dipole moment vectors cancel when they are at angles to one another (e.g. in a molecule with trigonal planar geometry)? Do we have to break up the vectors into their individual components?
Sun Nov 24, 2019 2:33 pm
Forum: Naming
Topic: Final Format
Replies: 6
Views: 53

Re: Final Format

I think the format of the final will be similar in format to the midterm, but slightly longer (3 hours long vs 2 hours long). I believe it is cumulative, so any material covered during the quarter is fair game. Hope this helps! :)
Sun Nov 17, 2019 6:01 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: single, double, and triple bonds
Replies: 6
Views: 74

Re: single, double, and triple bonds

Multiple bonds are treated as single regions of high electron density because these bonds always act as a single unit. Thus, any resonance structure of a particular molecule will have the same shape as determined by the VSEPR model. Hope this helps!
Sun Nov 17, 2019 5:51 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Dipole Moment
Replies: 3
Views: 42

Re: Dipole Moment

Yes, we can! A nonzero dipole moment implies that electrons are shared unequally by bonded atoms, resulting in the formation of partial charges.
Sun Nov 17, 2019 5:49 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: repulsion strength
Replies: 5
Views: 47

Re: repulsion strength

To add on the previous answer, lone pair repulsions are typically stronger than atom-atom repulsions because lone pairs are less restrained than bonds and take up more space!
Sun Nov 17, 2019 5:47 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: bond order calculations
Replies: 4
Views: 68

Re: bond order calculations

Bond order is determined by the type of bond (single, double, triple etc.) found between a pair of atoms. So, in order to determine the bond order, I would try drawing the lowest-energy Lewis structure for the molecule. For example, in the carbon monoxide molecule, the C-O bond order is 3 because ca...
Sun Nov 17, 2019 5:38 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Order
Replies: 3
Views: 54

Re: Bond Order

No, you do not need to know the bond order when finding the bond angle. Relating to the VSEPR model, I think the main concept regarding bond order that we have to be familiar with is that a multiple bond is treated as a SINGLE region of high electron density when determining the molecular shape.
Sun Nov 17, 2019 5:36 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR
Replies: 5
Views: 44

Re: VSEPR

VSEPR stands for the Valence Shell Electron Pair Repulsion Model. It is utilized to determine/explain the experimentally observed shapes of molecules by taking into account the various lone and bonding pairs of the molecule. Hope this helps!
Sun Nov 10, 2019 5:33 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Reference Table for VSEPR
Replies: 3
Views: 57

Re: Reference Table for VSEPR

Does anyone know if we will have to commit this information to memory for Test 2/Final exam? Will we be given this reference sheet during the exams? Thank you!
Sun Nov 10, 2019 5:27 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Hydrogen bonding
Replies: 7
Views: 48

Re: Hydrogen bonding

Can someone explain how hydrogen bonding affects the polarity of a molecule? I'm trying to understand the connection between these two concepts. Thank you so much!
Sun Nov 10, 2019 5:25 pm
Forum: Student Social/Study Group
Replies: 8
Views: 144

No :( I think the first time we will view our grades will be when they are posted on myUCLA. I'm not sure if they will be handing back the midterm in discussion section...
Sun Nov 10, 2019 5:24 pm
Forum: Ionic & Covalent Bonds
Topic: Covalent Character
Replies: 3
Views: 36

Re: Covalent Character

Just to add on to the previous replies, typically smaller cations and larger anions bonded together to increase the covalent character of a molecule. A smaller cation is able to more strongly attract electrons from the anion while a larger anion more easily shares electrons due to a weaker effective...
Sun Nov 10, 2019 5:20 pm
Forum: Lewis Structures
Replies: 26
Views: 464

I think each TA will grade one question to standardize grading across the board. So, multiple TAs?
Sun Nov 03, 2019 7:33 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: What are the octet exceptions?
Replies: 11
Views: 127

Re: What are the octet exceptions?

Based on the homework problems, an element that is commonly associated with an expanded octet (hypervalence) is the noble gas Xenon. Boron and Aluminum are two elements that often exist in compounds with an incomplete octet. Hope this helps!
Sun Nov 03, 2019 7:29 pm
Forum: Lewis Structures
Topic: expanding an octect
Replies: 5
Views: 64

Re: expanding an octect

Elements that are able to hold an expanded octet occur from Period 3 onwards because they have empty d-orbitals in their valence shell. They do not always have to hold more than 8 electrons. Typically, an expanded octet will consist of 10 or 12 electrons, but it may even be greater in particular cas...
Sun Nov 03, 2019 7:24 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge Purpose
Replies: 4
Views: 72

Re: Formal Charge Purpose

Just to add on, when a molecule has resonance structures, it's important to calculate the formal charge distribution of each structure. The resonance structure with the lowest formal charge makes the dominant contribution to the resonance hybrid because it is most energetically favorable (as you all...
Sun Nov 03, 2019 7:20 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic and Covalent Characteristics
Replies: 3
Views: 46

Re: Ionic and Covalent Characteristics

Just to add on, ionic bonds can also have covalent characteristics. The strong positive charge from a cation can induce distortion in the electron cloud of an anion resulting in electrons occupying the region between the two nuceli of the bonded atoms. This "sharing" of electrons between a...
Sun Nov 03, 2019 7:16 pm
Forum: Lewis Acids & Bases
Topic: diff b/w lewis acid and base
Replies: 12
Views: 160

Re: diff b/w lewis acid and base

A Lewis base is defined as a species that donates an electron pair (has lone pair electrons) while a Lewis acid is defined as a species that accepts an electron pair (has vacant orbitals). The acceptance of an electron pair by the Lewis acid from the Lewis base enables the formation of a coordinate ...
Fri Oct 25, 2019 9:44 am
Forum: Ionic & Covalent Bonds
Topic: Ionization Energy
Replies: 4
Views: 74

Re: Ionization Energy

Elements with low ionization energy tend to form cations because it is easier (requires less energy) to remove electrons from their orbitals. Thus, the formation of a positively charged ion (cation) is favored. The characteristic of having low ionization energy also enables these elements (metals) t...
Thu Oct 24, 2019 10:34 am
Forum: Ionic & Covalent Bonds
Topic: Ionic Compounds
Replies: 6
Views: 108

Re: Ionic Compounds

Just to add on to the previous replies, the cations and anions of an ionic compound are bonded together in a crystalline formation (I think of a cube). So, that's basically rows of alternating cations (+) and anions (-) attached to each other. Hope this helps you get a better picture of how ionic bo...
Thu Oct 24, 2019 10:27 am
Forum: Trends in The Periodic Table
Topic: Effective Nuclear Charge
Replies: 5
Views: 90

Re: Effective Nuclear Charge

Can someone explain how trends in effective nuclear charge explain the trends in electron affinity? I'm kind of confused because electron affinity does not have the same "periodic nature" as the other properties of elements. Thank you!
Thu Oct 24, 2019 10:18 am
Forum: Ionic & Covalent Bonds
Topic: Double Bond vs Single Bond Length
Replies: 6
Views: 171

Re: Double Bond vs Single Bond Length

I spoke with an LA after class about this specific topic. He explained that the electrons of the NO3- ion are evenly distributed amongst the three bonds. Thus, in reality, there is no distinguishable difference between the double/single bonds. This is the reasoning behind the experimental 1.24-angst...
Thu Oct 24, 2019 7:40 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Lowest Energy for Elements, Compounds, Etc
Replies: 2
Views: 52

Re: Lowest Energy for Elements, Compounds, Etc

Based on physical laws, it is typically more energetically favorable for compounds formed through covalent/ionic bonding to have a lower energy state than the elements that make them up. Since ionic/covalent compounds have a lower energy state than their constituents, they are often much more stable...
Sun Oct 20, 2019 1:27 pm
Forum: Trends in The Periodic Table
Topic: Trends in Electron Affinity
Replies: 3
Views: 68

Trends in Electron Affinity

Is there a clear trend for electron affinity across a period/down a group (as for atomic/ionic radii)? Do you have any helpful tips for remembering the trend/exceptions to the rule? I struggled with this topic in AP chem, so I'd really appreciate any insight :) Thank you so much!
Sun Oct 20, 2019 1:18 pm
Topic: Energy of photons
Replies: 4
Views: 184

Re: Energy of photons

1. E = hv calculates the energy contained by an individual photon of light 2. E = 1/2 mv^2 is the formula for the kinetic energy of any object with a mass. Since photons are assumed to be massless, you cannot use this formula to calculate their energy. Oftentimes, the formula for kinetic energy is u...
Sun Oct 20, 2019 1:15 pm
Forum: Quantum Numbers and The H-Atom
Topic: d orbitals
Replies: 4
Views: 86

Re: d orbitals

If the 3d orbital is filled after the 4s orbital, then why does it have less energy? Wouldn't electrons tend to fill subshells with lower energy first? Can someone please explain why this is the case? Thank you!
Sun Oct 20, 2019 1:12 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: 1B 27
Replies: 2
Views: 51

Re: 1B 27

1. By Heisenberg's Uncertainty Principle: (uncertainty in momentum)(uncertainty in position) >/= (h)/(4 pi) 2. The given values in this problem allow you to calculate the uncertainty in momentum. Then, using Heisenberg's Uncertainty Principle, you must solve for the uncertainty in the position. 3. u...
Sun Oct 20, 2019 12:58 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Ordering of s and d orbitals
Replies: 4
Views: 59

Ordering of s and d orbitals

In my AP Chem class, I learned to write the 4s subshell before the 3d subshell when writing an electron configuration. However, during the lecture and in the examples/problems from the textbook, the 3d orbital is written prior to the 4s orbital. (I also remember Dr. Lavelle saying that this is the p...
Sun Oct 20, 2019 12:58 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Ordering of s and d orbitals
Replies: 2
Views: 38

Ordering of s and d orbitals

In my AP Chem class, I learned to write the 4s subshell before the 3d subshell when writing an electron configuration. However, during the lecture and in the examples/problems from the textbook, the 3d orbital is written prior to the 4s orbital. (I also remember Dr. Lavelle saying that this is the p...
Sun Oct 13, 2019 10:34 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect
Replies: 3
Views: 76

Re: Photoelectric Effect

I thought that the excited electrons are released from the hydrogen atom in the case of atomic spectra? Can you please clarify what you mean when you say that the electron is still "attached"? Thank you!
Sun Oct 13, 2019 10:27 pm
Forum: Photoelectric Effect
Topic: Symbol N Subscript A
Replies: 2
Views: 58

Re: Symbol N Subscript A

The symbol N subscript A stands for the number of photons in 1 mol of photons (so, by definition, Avogadro's number of 6.02 * 10^23 photons). The example asks to find the total amount of energy in 1 mol of photons. So, we have to multiply the energy of a single photon by the total number of photons ...
Sun Oct 13, 2019 10:18 pm
Topic: Black Body
Replies: 6
Views: 238

Re: Black Body

Can someone explain how black body radiation is related to the photoelectric effect?
Sun Oct 13, 2019 10:14 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg equation [ENDORSED]
Replies: 73
Views: 3712

Re: Rydberg equation[ENDORSED]

The final units of your answer depend on what you are solving for. The principal energy levels (n1 and n2) do not have units. However, if you are solving for the wavelength using the Rydberg equation, the final units of your answer must be meters (or some other measurement of length). For reference,...
Sun Oct 13, 2019 10:00 pm
Forum: Photoelectric Effect
Topic: Wavelength, Frequency, and Intensity
Replies: 7
Views: 67

Re: Wavelength, Frequency, and Intensity

Is there a particular equation relating intensity to other variables? I'm still a little confused why intensity plays no role at all in the photoelectric effect. Thanks!
Tue Oct 01, 2019 11:56 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: How do I do problem E.3 on page F45 of the textbook?
Replies: 4
Views: 120

Re: How do I do problem E.3 on page F45 of the textbook?

I think you need to refer to the diagram of the scale shown below the problem in order to find the solution. If you look at the picture, there are 9 blue gallium atoms on the left side of the scale. Looking at your periodic table, the molar mass of astatine (210 g) is approximately three times great...
Tue Oct 01, 2019 11:39 pm
Forum: Molarity, Solutions, Dilutions
Topic: Post- Assessment Problem 16
Replies: 2
Views: 69

Re: Post- Assessment Problem 16

Well, first you'd use the calculated molar mass of KCl (74.5513 g/mol) to convert the mass of KCl into moles of KCl: 5.51 g KCl * 1 mol KCl/74.5513 g KCl = 0.739 mol KCl Then, the problem states that water is added to a final volume of 125 mL. Basically this means that water was poured into the cont...
Tue Oct 01, 2019 11:30 pm
Forum: Limiting Reactant Calculations
Topic: Post-Module Assessment Question 18
Replies: 6
Views: 125

Re: Post-Module Assessment Question 18

On a side note, I'd like to point out that the equation was incorrectly written in the original question. There is no subscript 2 for the oxygen gas on the product side of the equation. Nitrogen monoxide NOT nitrogen dioxide is formed! The entire correct equation is written below: 4NH[3] + 5O[2]--> ...
Tue Oct 01, 2019 11:25 pm
Forum: Limiting Reactant Calculations
Topic: Post-Module Assessment Question 18
Replies: 6
Views: 125

Re: Post-Module Assessment Question 18

Well, in the balanced equation 4NH3 + 5O2 --> 4NO + 6H20, the ratio NH3 to O2 = 4:5. If you divide both sides of this ratio by 4 you get 1: 1.25. That is why you have to multiply the number of moles of NH3 by 1.25 to get the required moles of O2.
Tue Oct 01, 2019 11:03 pm
Forum: Limiting Reactant Calculations
Topic: Post-Module Assessment Question 18
Replies: 6
Views: 125

Re: Post-Module Assessment Question 18

I compared the experimental mole ratios of NH3 and O2 to the ratios of the stoichiometric coefficients given in the problem. As you probably calculated: 21.4 g NH3 = 1.2566 mol NH3 42.5 g O2 = 1.328125 mol O2 In the reactant side of the given chemical equation, the ratio of NH3: O2 = 4:5. Based on t...
Tue Oct 01, 2019 10:50 pm
Forum: Molarity, Solutions, Dilutions
Topic: How to do E15
Replies: 4
Views: 70

Re: How to do E15

In the last sentence, I think you meant to say add the molar mass of Calcium (39.94g/mol) to the molar mass of a Sulfide ion (32.05 g/mol) in order to find the solution.