## Search found 36 matches

Tue Jun 05, 2018 11:55 am
Forum: Bronsted Acids & Bases
Topic: J11c
Replies: 4
Views: 405

### Re: J11c

Hi Emily,
Another non perfect way of looking at CaO as the base is knowing that O is oftentimes basic.
Oftentimes, things with H are acidic. This is not always true, but in this case the compound has the name acid in it.
Tue Jun 05, 2018 11:46 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Assuming X is small
Replies: 2
Views: 332

### Re: Assuming X is small

For bases, the x represents [OH¯], and the the orginal starting concentration is represented by [B]o. In Kb calculations, the term '[B]o minus x' would have the 'minus x' dropped.There is a 5% rule for bases as described by Ravi. The approximation for x is valid if and only if (x /[B]o)* 100 is equa...
Tue Jun 05, 2018 11:34 am
Forum: Lewis Acids & Bases
Topic: Lewis and Bronsted Acid/Bases
Replies: 2
Views: 234

### Re: Lewis and Bronsted Acid/Bases

Hi Elizabeth, I believe that Lewis acids AND bases are a generalization of Bronsted acids and bases. Since a Lewis acid is anything that accepts an electron pair, the definition of a Bronsted acid, as something that accepts electrons at an acidic hydrogen, is comprised within the definition of a Lew...
Tue May 29, 2018 9:16 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: HW 4.9
Replies: 10
Views: 1084

### Re: HW 4.9

Hi Alexa,
If this molecule were trigonal planar, it would have only 3 bonds and zero LP. As Sloene stated, molecules that are t-shaped have either 5 bonds and 2 lone pairs OR 6 bonds and 3 lone pairs. In both of these cases the angle is less than 90 degrees.
Tue May 29, 2018 9:13 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: HW 4.19 part b and d
Replies: 3
Views: 236

### Re: HW 4.19 part b and d

Hi Anna, b) That would be okay for the lewis structure, but not okay for the VSEPR model. Tetrahedral, with each angel at 109.5 degrees is the correct answer. This is the case because there are 3 bonds, and 0 LP. d) In every case, you prefer the model that satisfies the octet rule. Formal charge wou...
Tue May 29, 2018 9:08 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: General Molecular Shape
Replies: 3
Views: 193

### Re: General Molecular Shape

Hi Bree, You can first look at the number of "things" bonded to the central atom, these can be lone pairs or bonded electrons. The number of lone pairs that the central atom has, combined with the number of "bonds" determines the shape. For example, if there are 0 LP and 2 "...
Mon May 21, 2018 8:59 am
Forum: Octet Exceptions
Topic: Octet exceptions
Replies: 1
Views: 224

### Re: Octet exceptions

Hi Kalsuda, The octet rule can be broken by almost any of the elements. It is more of a shaky guideline, than it is a "rule." The area you are describing is filled with mostly transition metals. These D block elements tend to lose or gain a few valence electrons, but sometimes not enough t...
Mon May 21, 2018 8:50 am
Forum: Resonance Structures
Topic: COVALENT VS IONIC LEWIS STRUCTURES [ENDORSED]
Replies: 1
Views: 201

### Re: COVALENT VS IONIC LEWIS STRUCTURES[ENDORSED]

Hi April, First you would count up the number of valance electrons in each atom. So Aluminum has 3, and Chlorine has 7(3). You place Al in the center, since it is the least electronegative and put the Cl's around the outside. You know you have 24 electrons in total. You begin with drawing single bon...
Mon May 21, 2018 8:41 am
Forum: Ionic & Covalent Bonds
Topic: Significance to the different interactions [ENDORSED]
Replies: 1
Views: 143

### Re: Significance to the different interactions[ENDORSED]

Hi Husnia, First you need to know the an ion is a molecule with charge, due to a gained or lost electron. Also it would be helpful to know that a dipole is a molecule that has a concentrated positive charge separated from a concentrated negative charge. Ion-ion: these are interactions between ions w...
Tue May 15, 2018 10:25 am
Forum: Resonance Structures
Topic: How do Resonance Structures Work?
Replies: 4
Views: 337

### Re: How do Resonance Structures Work?

Hi Myles, I believe that resonance structures are just alternative forms of an acceptable Lewis Structure. Since a molecule can be represented in many ways, the actual way would be a combination of the two. Since bonding can not be expressed in one way, the resonance structure shows that electrons a...
Tue May 15, 2018 10:21 am
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge terms
Replies: 2
Views: 207

### Re: Formal Charge terms

Hi Maria, This is what each of the terms mean: FC (Formal Charge)- the charge that is given to a molecule, assuming equal sharing of electrons in chemical bonds. VE (Valance Electrons)- outer shell electrons that participate in bonding. In order to find the VE, in the first and second period, the nu...
Tue May 15, 2018 10:16 am
Forum: Lewis Structures
Topic: Ionic Lewis Structures
Replies: 2
Views: 243

### Re: Ionic Lewis Structures

Hi Tiffany,
Lets say the compound was sodium chloride. You would write Na+ [Cl]-. Inside the brackets for Cl you would fill Cl octet. In other words there would be two dots on each side of Cl. It is not that you are ignoring Na's electrons, instead it is that Cl recieves them.
Tue May 15, 2018 10:08 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Drawing Lewis Structures
Replies: 5
Views: 375

### Re: Drawing Lewis Structures

Hi Endri,
It does not matter in this case, it is one form of a few resonance structures. Basically this means that a Lewis Structure can be drawn in more ways than one.
Mon May 07, 2018 5:15 pm
Forum: Quantum Numbers and The H-Atom
Topic: difference between electron orbital and electron subshell?
Replies: 2
Views: 480

### Re: difference between electron orbital and electron subshell?

Visually, an orbital is the wave function, it makes the picture 3d, it adds the z axis. Each orbital can hold a maximum of 2 electrons. Whereas the sub shell is 2 dimensional, this is one or more orbitals that have the same energy level. We can tell it is part of something else by looking at the pre...
Mon May 07, 2018 5:11 pm
Forum: Trends in The Periodic Table
Topic: Electron Affinity Trend
Replies: 2
Views: 540

### Re: Electron Affinity Trend

I also like to think about this in that it increases as a vector from the bottom left corner to the top right. So an element like Chlorine would have a very high electron affinity, and an element like Thallium would have a very low electron affinity.
Mon May 07, 2018 5:06 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Valance electrons for d-orbital
Replies: 2
Views: 283

### Re: Valance electrons for d-orbital

Another good tip is to remember that d-block elements have the number of valence electrons that is equal to their group number. In turn, their group number is equal to the number of electrons in the "valence shell"(the outermost shell).
Mon May 07, 2018 5:03 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 2.51
Replies: 2
Views: 205

### 2.51

I am about the way in which the f block fills. For the element Bi, I know it would begin [Xe] and then I believe it would continue 4f^14 5d^10 6s^2 6p^3. Do I just have to memorize that the f block fills first, when the 5d block is in play?
Mon Apr 30, 2018 9:10 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration of Ag
Replies: 3
Views: 736

### Re: Electron Configuration of Ag

Hi Rebecca,
The electronic configuration of silver, [Kr]4d^10 4s^1, is this way because atoms become more stable this way. It is the most stable when the 4d electron is completely filled.
Mon Apr 30, 2018 8:55 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Homework 2.55 part c
Replies: 3
Views: 221

### Re: Homework 2.55 part c

Hi Natalie,
2.55(c) actually has a typo, as stated in Dr. Lavelle's correction to the textbook problems the correct answer is actually (n-1) d^3 ns^2. You were right!
Mon Apr 30, 2018 8:44 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: f orbitals
Replies: 3
Views: 195

### Re: f orbitals

Even though we do not need to know how to use f orbitals at all in Chem 14A, they would be used for high energy levels. At the fourth and other levels that are higher, there are seven f orbitals in addition to the 4s, 4p, and 4d orbitals. An example may be Eu, Europium, whose electron configuration ...
Mon Apr 30, 2018 8:37 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Energy, subshells, shells???
Replies: 1
Views: 164

### Re: Energy, subshells, shells???

Hi Haison,
I just posted a response to a question very similar to yours, check Anna De Schutter's post "Terminology with quantum numbers." Hope this helps!
Mon Apr 30, 2018 8:34 pm
Forum: Quantum Numbers and The H-Atom
Topic: Terminology with quantum numbers
Replies: 3
Views: 292

### Re: Terminology with quantum numbers

Hi Anna, - When they ask for the number of orbitals, does that mean the quantum number ml - The quantum number ml refers to the magnetic quantum number. This number is in charge of determining the number of orbitals, and what their rotation is in the sub shell. It can be negative, zero, or positive....
Fri Apr 27, 2018 12:10 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Emission vs Absorption
Replies: 3
Views: 253

### Re: Emission vs Absorption

Hi Madeline, I am pretty sure that you can use either the light absorbed or emitted to get the same answer. You would just plug in the value accordingly. You can still use the Rydberg equation to predict the wavelength of light resulting from an electron moving between energy levels of an atom, whet...
Fri Apr 27, 2018 12:04 pm
Forum: Quantum Numbers and The H-Atom
Topic: Angular Momentum Quantum Numbers
Replies: 1
Views: 151

### Angular Momentum Quantum Numbers

I am confused on what angular momentum quantum numbers are. In my lecture notes, I wrote that they describe the shape. Dr. Lavelle said that they have allowed values of l=0,l=1, l=2.... n-1. Can someone please explain what the n minus one means. I do not understand how this could be a possible value.
Fri Apr 27, 2018 11:50 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Wave peak differences
Replies: 2
Views: 139

### Re: Wave peak differences

Hi Nimrat,
Annie is right, it would always be destructive interference in this case. To elaborate, the only way to get constructive interference would be to have two peaks overlapping, creating a larger peak. I like to think of destructive interference as destroying, or making smaller.
Tue Apr 17, 2018 10:33 am
Forum: Einstein Equation
Topic: When to use E=hc/wavelength
Replies: 6
Views: 612

### Re: When to use E=hc/wavelength

Hi Isabelle, These various equations are used for finding different things. For example if you are asked to find the energy you can not use c= wavelength*frequency, because in this case energy is not even in the equation given. If you are asked to find energy you should use one of the other two equa...
Tue Apr 17, 2018 10:24 am
Forum: Photoelectric Effect
Topic: Energy levels
Replies: 7
Views: 1213

### Re: Energy levels

Hi Paula, The gap between the first two energy levels, n1 and n2, is the largest because these two values have the largest difference between the excited and ground state. For example, a drop from n2 to n1 has ALOT more energy than a drop from n4 to n1. Energy levels are also closer together as you ...
Tue Apr 17, 2018 10:14 am
Forum: Properties of Light
Topic: Reference Point
Replies: 1
Views: 124

### Re: Reference Point

Hi Cindy, I think what Dr. Lavelle was trying to explain here is that this formula can only be used for the spectra of atomic hydrogen. The reference point differs for each element, when that electron is completely removed the energy is at 0. As n approaches infinity, energy approaches 0. So the ref...
Tue Apr 17, 2018 10:05 am
Forum: Properties of Light
Topic: Planck's constant
Replies: 1
Views: 100

### Re: Planck's constant

Planck's constant relates the energy in one photon of electromagnetic radiation to the frequency of that radiation. It is a constant given by the letter h, with the value 6.626176 x 10-34 Js.
Tue Apr 10, 2018 8:27 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Using Precision and Accuracy to Solve A Problem
Replies: 3
Views: 280

### Re: Using Precision and Accuracy to Solve A Problem

Hi Perla, YES! Both precision and accuracy are wonderful to have in solving for the correct answer. The combination of these two factors tend to lead to a correct answer. Even though precision is technically not an indication of the true value, being precise is similar to being consistent. While pre...
Tue Apr 10, 2018 8:23 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Formula Units
Replies: 6
Views: 9624

### Formula Units

I am confused on what formula units are. I see them coming up in a lot of the problems from outline 1, but have never learned about them in lecture or elsewhere. How do we find formula units? Also, is it always imperative that we convert them to moles?
Tue Apr 10, 2018 8:19 pm
Forum: Significant Figures
Topic: Scientific notation [ENDORSED]
Replies: 7
Views: 561

### Re: Scientific notation[ENDORSED]

Hi Kalsuda, I do not think that there is heavy emphasis on neither sig figs or scientific notation this quarter. Personally, I am uncomfortable working with scientific notation, so I will oftentimes convert numbers that are given to me in scientific notation into decimals and change them back for my...
Tue Apr 10, 2018 8:15 pm
Forum: SI Units, Unit Conversions
Topic: Units for Answer
Replies: 10
Views: 710

### Re: Units for Answer

Hi Maria, Read the problems carefully, they will sometimes tell you what units to answer the question in. If the problem does not specify what they would like your end result in, then it is standard to give it in grams for example. Additionally, be cautious to convert from kg to g at the start of th...
Wed Apr 04, 2018 11:52 am
Forum: Limiting Reactant Calculations
Topic: Module 3: Limiting Reactant Calculations, Question 19
Replies: 4
Views: 513

### Module 3: Limiting Reactant Calculations, Question 19

I am also confused on this question from the third assessment Dr. Lavelle posted. For the following reaction if 1.00 x 102 g H2O reacts with 1.00 x 102 g CaC2 identify the limiting reactant. CaC2(s) + H2O(l) ---> Ca(OH)2(aq) + C2H2(g) After balancing the equation and calculating the molar mass, I fo...
Wed Apr 04, 2018 11:39 am
Forum: Limiting Reactant Calculations
Topic: Limiting Reactant Calculations [ENDORSED]
Replies: 3
Views: 396

### Re: Limiting Reactant Calculations[ENDORSED]

The question is asking you for the amount of moles of CO2 that are produced and you can assume that CaCO3 is the limiting reactant since it is what is being used to neutralize the acid spill. After you calculate the molar mass of CaCO3(approximately 10 moles), you look at the ratio between CaCO3 and...
Wed Apr 04, 2018 11:29 am
Forum: Limiting Reactant Calculations
Topic: Module 3: Limiting Reactant Calculations, Question 26 [ENDORSED]
Replies: 4
Views: 358

### Module 3: Limiting Reactant Calculations, Question 26[ENDORSED]

I do not know how to solve this problem. "Based on the molar ratios in a balanced chemical equation a student expects 0.20 moles of product. If the molar mass of the product is 81 g.mol-1 what is the theoretical yield?" I tried dividing 0.20 mol by 81 g/mol and I got .002 moles. I thought ...

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