## Search found 50 matches

Mon Dec 09, 2019 9:49 am
Forum: Lewis Acids & Bases
Topic: Strong/Weak Acids and Bases
Replies: 4
Views: 181

### Re: Strong/Weak Acids and Bases

For future reference regarding the bases, I think BeO (despite being a group 2 oxide) is actually an amphoteric oxide, not a base.
Mon Dec 09, 2019 9:46 am
Forum: Student Social/Study Group
Topic: heme complex
Replies: 5
Views: 273

### Re: heme complex

I thought it had 6? When you look it up, images like this come up:

So 5 nitrogens, 1 oxygen.
Mon Dec 09, 2019 9:42 am
Forum: Student Social/Study Group
Topic: Final Jitters
Replies: 189
Views: 34551

### Re: Final Jitters

It's a little late for this final - but for future ones, you can try avoiding or reducing caffeine (if you aren't already). Caffeine definitely increases anxiety. If you need the caffeine to study, make sure you don't take it on an empty stomach.
Fri Dec 06, 2019 5:34 pm
Forum: Lewis Structures
Topic: SO3 Lewis Structure
Replies: 1
Views: 173

### SO3 Lewis Structure

I drew the Lewis structure of SO3 with the S in the middle and double bonded to each oxygen atom. Each oxygen atom then has two lone pairs, and everything has FC = 0. But, in 6.5, the textbook has the lewis structure of SO3 with S double bonded to one of the oxygens and single bonded to the other tw...
Fri Dec 06, 2019 2:03 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Sig Figs in 6B3
Replies: 3
Views: 66

### Sig Figs in 6B3

6B3 says "A careless laboratory technician wants to prepare 200.0 mL of a 0.025 M HCl(aq) solution but uses a volumetric flask of volume 250.0 mL by mistake. (a) What would the pH of the desired solution have been? (b) What will be the actual pH of the solution as prepared?" The textbook s...
Sun Dec 01, 2019 8:30 pm
Forum: Naming
Topic: H20 vs 0H-
Replies: 2
Views: 54

### Re: H20 vs 0H-

I think you might be misreading the answers. Aqua always refers to water, which can be written as either H2O or OH2 (which I think you're mistaking for OH-). The textbook writes water as OH2 to emphasize the oxygen is doing the bonding I believe.
Sun Dec 01, 2019 8:25 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: 6C.21
Replies: 2
Views: 43

### Re: 6C.21

They both have resonance I think. But, an acid is stronger if its conjugate base is more stable. Conjugate bases are stabilized by electron attracting atoms (delocalization of electrons) and destabilized by electron releasing groups. CH3 is more prone to electron donation/release than H is, so the c...
Sun Dec 01, 2019 8:06 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Inorganic or Organic
Replies: 6
Views: 109

### Re: Inorganic or Organic

Organic acids contain carbon whereas inorganic ones do not.
Sun Dec 01, 2019 4:18 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Oxidation Number
Replies: 2
Views: 72

### Re: Oxidation Number

The oxidation number of an atom in a compound is the charge that atom would have if the compound was separated into ions. In general, to figure out oxidation numbers, you look at the overall charge and at atoms that always have the same oxidation number to figure out the ones that can vary. There ar...
Sun Dec 01, 2019 4:03 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Oxoacids and Carboxylic Acids
Replies: 1
Views: 41

### Re: Oxoacids and Carboxylic Acids

I think all carboxylic acids are weak acids whereas some oxyacids are strong acids (H2SO4 and HNO3 for example),so maybe, in general, oxyacids are stronger. They're also inorganic whereas carboxylic are organic and I think Prof. Lavelle said inorganic acids are usually stronger.
Sun Nov 24, 2019 7:57 pm
Forum: Hybridization
Topic: dsp3 vs sp3d
Replies: 4
Views: 74

### Re: dsp3 vs sp3d

He said he chose to write it that way so he'd remember to tell us that the order doesn't matter.
Sun Nov 24, 2019 7:54 pm
Forum: Hybridization
Topic: Hybridization Concept
Replies: 1
Views: 38

### Re: Hybridization Concept

They exist because not all the p orbitals have to be hybridized. For example, Lavelle talked about C2H4 in class. Each carbon has a 2sp2 hybridization because they each have 3 regions of electron density. One electron stays in a non-hybridized 3p orbital. This makes sense because then the electron i...
Sun Nov 24, 2019 6:28 pm
Forum: Hybridization
Topic: Hybridization
Replies: 3
Views: 45

### Re: Hybridization

I think the easiest way to think of it is that hybridization comes from the distribution of the electrons (looking at lone pairs and bonds). So, to figure out the hybridization, you'd first want to look at the electron density. Ex: CH4 and H2O both have 4 regions of electron density, so the hybridiz...
Sun Nov 24, 2019 6:14 pm
Forum: Hybridization
Topic: Valence Bond (VB) Theory
Replies: 1
Views: 45

### Re: Valence Bond (VB) Theory

VB theory uses orbitals to describe covalent bonding. Each unpaired valence electron can form a covalent bond. It needs hybridization to adequately do so because otherwise, the bonding tendencies of elements like carbon would not make sense. Ex: Carbon has 2 unpaired valence electrons in the 2p shel...
Sun Nov 24, 2019 6:00 pm
Forum: Hybridization
Topic: Describing a molecule using hybridization
Replies: 4
Views: 40

### Re: Describing a molecule using hybridization

I think the steric number is just part of the thought process for determining the hybridization, so you should give both or just the hybridization.
Sat Nov 16, 2019 5:44 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Structure of H2SeO4
Replies: 1
Views: 55

### Re: Structure of H2SeO4

I think it's polar because acids tend to be and it looks like this: H2SeO4.jpg My guess is you'd draw the negative dipole moment arrows going towards the various oxygens, from both the Se and the H. So the oxygens bonded to both the Se and H would have a negative dipole moment in both bonds and be m...
Sat Nov 16, 2019 5:27 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Octahedral Arrangement
Replies: 2
Views: 54

### Re: Octahedral Arrangement

The textbook does mention a pentagonal bipyramidal structure which is 7 regions of electron density, but I don't see anything past that. Maybe molecules past 7 regions of electron density don't really exist due to too much electron repulsion or something - the bond angles get too small? Or, they're ...
Sat Nov 16, 2019 4:36 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 2E.19b
Replies: 2
Views: 34

### Re: 2E.19b

The textbook said you can just consider each central atom individually. So, both carbons have 4 bonds (3 C-H and 1 C-Be) and no lone pairs. This makes them both have tetrahedral structure and bond angles of 109.5. The Be has two bonds (both Be-C) so this gives it the linear structure and a bond angl...
Sat Nov 16, 2019 4:27 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR
Replies: 3
Views: 61

### Re: VSEPR

The chart is great but to understand it you could think of a seesaw molecule like SF4 like this: 1. SF4 has 5 regions of electron density because the lone pair is kinda like another S-F bond. So, I think of trigonal bipyramidal as the "template" shape because that's what's formed by centra...
Sat Nov 16, 2019 4:09 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: polar vs nonpolar
Replies: 6
Views: 80

### Re: polar vs nonpolar

You really can't tell just from the formula unless it's something really simple like a diatomic molecule (H2, O2, etc are always non polar because their only bond is non polar). Additionally, Lewis structures can be helpful, but they can also be misleading. For example, you could draw the Lewis stru...
Sat Nov 09, 2019 7:46 pm
Forum: Dipole Moments
Topic: Dipole Dipole
Replies: 3
Views: 29

### Re: Dipole Dipole

A dipole-dipole moment will always occur between two elements of different electronegativity bonded together. It will be more extreme between atoms of very different electronegativity (like Cl and H).
Sat Nov 09, 2019 7:41 pm
Forum: Dipole Moments
Topic: BOND STRENGTH
Replies: 4
Views: 42

### Re: BOND STRENGTH

Can you give an example molecule? Generally I don’t think whether the molecule has single/double/etc bonds has much to do with whether it’s polar or not.
Sat Nov 09, 2019 7:38 pm
Forum: Dipole Moments
Topic: Electronegativity on Dipoles
Replies: 3
Views: 33

### Re: Electronegativity on Dipoles

Yes, if the elements have different electronegativities, you should consider the bond to have a dipole moment. This is because the element with the higher electronegativity is pulling the electrons closer to it, making it slightly negative and the other element slightly positive.
Sat Nov 09, 2019 7:33 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Polairzability characteristics
Replies: 3
Views: 74

### Re: Polairzability characteristics

Also, the more polarizable an atom or molecule is, the greater the intermolecular induced-dipole induced-dipole forces. Since those forces are greater, it takes more energy to reach the liquid or gas phase. Ex: Cl2 is a gas at room temperature because the interactions between the Cl2 molecules are w...
Tue Nov 05, 2019 5:12 pm
Forum: Lewis Structures
Topic: Lewis Structure HClO3
Replies: 2
Views: 53

### Lewis Structure HClO3

Question 2C3 asks for the lewis structure of HClO3. I came up with the structure below in which I think everything has a formal charge of 0, and there are no expanded octets. IMG_1948.jpg But in reality, it has an expanded octet on chlorine and resonance as its most stable structure (furthest right)...
Sat Nov 02, 2019 4:51 pm
Forum: Lewis Structures
Topic: Determining most stable Lewis structure
Replies: 5
Views: 94

### Re: Determining most stable Lewis structure

The least electronegative atom (in this case, nitrogen) being the central atom is also important.
Sat Nov 02, 2019 4:48 pm
Forum: Lewis Structures
Topic: drawing lewis structures
Replies: 5
Views: 83

### Re: drawing lewis structures

To figure out this lewis structure... 1. Count the valence electrons. Each F has 7 and Br has 7 as well, so there need to be 28 in total. 2. Determine Br is the central atom because it has the lower electronegativity. 3. F is not flexible octet wise, so we know each one needs a single bond with the ...
Sat Nov 02, 2019 4:36 pm
Forum: Octet Exceptions
Topic: expanded octet for P
Replies: 2
Views: 57

### Re: expanded octet for P

That is confusing. One explanation I found online says "although the energy of empty 3d-orbitals is ordinarily higher than that of the 4s orbital, that difference is small and the additional d orbitals can accommodate more electrons." Or vaguely, on another site, that somehow excitation of...
Sat Nov 02, 2019 2:27 pm
Forum: Octet Exceptions
Topic: Exceptions?
Replies: 5
Views: 87

### Re: Exceptions?

As mentioned above, the elements in group 3 can break the octet rule likely by forming an expanded octet. This is because they have access to the unfilled 3d orbitals for bonding. I think other groups above n=2 can also access their respective unfilled d-orbitals to have expanded octets. Additionall...
Mon Oct 28, 2019 7:10 pm
Forum: Ionic & Covalent Bonds
Topic: D-orbital electrons counting as valence or not.
Replies: 2
Views: 57

### D-orbital electrons counting as valence or not.

I'm a little confused about when d-orbital electrons count as valence electrons. For example, in problem 2A1, Sb is considered to have 5 valence electrons. I assume those electrons are the 3 in the 5p shell and the 2 in the 5s shell. If that is the case, the 10 4d electrons are not considered valenc...
Sat Oct 26, 2019 3:23 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge Formula
Replies: 5
Views: 64

### Re: Formal Charge Formula

The shared electrons are the ones involved in bonding (the lines in Lewis structures). Each line counts as two shared electrons (so a double bond is 4 shared electrons). For example, in H2O, the oxygen has 4 shared electrons because it has a single bond with each hydrogen. It then has 4 lone electro...
Sat Oct 26, 2019 2:35 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge and Molecules
Replies: 4
Views: 85

### Re: Formal Charge and Molecules

Also, when adding up the FCs to get the overall molecule charge, it is important to remember that the negative formal charges should be on the more electronegative elements and the positive formal charges on the less electronegative elements.
Sat Oct 26, 2019 2:30 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Checking bonding
Replies: 3
Views: 95

### Re: Checking bonding

I don't think so since even checking formal charge I don't think can tell you if you're correct - it can just tell you which potential lewis structures are better/more likely to be correct. But, when it comes to figuring out a good lewis structure that is likely to be experimentally correct, you can...
Sat Oct 26, 2019 11:59 am
Forum: Ionic & Covalent Bonds
Topic: Expanded Valence Shells
Replies: 4
Views: 46

### Re: Expanded Valence Shells

Expanded valence shell = element having more than octet. They occur for elements n=3 and above because the element can make use of empty d orbitals for bonding. For example, sulfur is [Ne]3s^2 3p^4 in its ground state. So, you might expect it to only “have room” for two more electrons to fill the 3p...
Sat Oct 26, 2019 11:53 am
Forum: Ionic & Covalent Bonds
Topic: Partial Bond
Replies: 2
Views: 40

### Re: Partial Bond

To add on, partial bonds have bond lengths that are also a blend b/w the two structures. So, since the nitrate bonds can be thought of as a blend between double and single bonds, the length is between that of a double (shorter) and single bond (longer) involving nitrogen and oxygen in a non-resonanc...
Sat Oct 19, 2019 4:28 pm
Forum: Properties of Electrons
Topic: Photo and electron energy
Replies: 4
Views: 53

### Re: Photo and electron energy

I think Wesley is correct because if higher than needed energy photons were absorbed, I think that would mean that material that absorbs red light (λ = 700) would also absorb all other colors of light since they are higher energy. But that isn't the case because we can see colors like blue being ref...
Sat Oct 19, 2019 4:14 pm
Forum: Properties of Electrons
Topic: Velocity
Replies: 1
Views: 53

### Re: Velocity

Are you referencing the Ep = Ek + ϕ equation where Ek = 1/2mv^2? If so, it's helpful I think to compare the electron removal to rolling a ball. It takes a certain amount of your energy (pushing) to overcome the initial friction and get the ball moving. That is the ϕ for the electron. Any extra energ...
Fri Oct 18, 2019 1:18 am
Forum: Properties of Light
Topic: Unit Conversions
Replies: 6
Views: 102

### Re: Unit Conversions

I'm sure it's different for everyone, but personally I find it easiest to just convert to meters in the middle since we know the conversion factors relating to meters. Ex: Convert 400 nm to pm. (400 nm) x (1 m/10^9 nm) x (10^12 pm/1 m) = 400,000 pm You can tell that all the units except pm cancel. A...
Fri Oct 18, 2019 1:09 am
Forum: Properties of Light
Topic: Where to find equations?
Replies: 5
Views: 77

### Re: Where to find equations?

This is the link to the equation sheet Dr. Lavelle has on his website: https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14A/constants_equations.pdf I think it has all the necessary quantum equations. If the link doesn't work, you can find it under the "constants and equations"...
Fri Oct 18, 2019 1:00 am
Forum: Properties of Light
Topic: Unit for Wavelength
Replies: 34
Views: 428

### Re: Unit for Wavelength

The standard unit for wavelength is just meters since it is a distance. You should have wavelength in meters when doing calculations so the units will cancel properly. However, often we are given the value in nanometers (in which case you'd want to convert the value to meters as your first step) or ...
Fri Oct 11, 2019 1:53 am
Forum: Properties of Light
Topic: Emission/line spectrum
Replies: 3
Views: 52

### Re: Emission/line spectrum

Well, it is relevant in that visible light corresponds to the Balmer series. So, when we are given the wavelength of emitted light (and it is in the visible portion of the spectrum) and we have to find the initial and final n, we know that the final n is 2. And we can get the energy and frequency fr...
Fri Oct 11, 2019 1:37 am
Forum: Properties of Light
Topic: models of light
Replies: 5
Views: 124

### Re: models of light

I'm not sure how to know when to use each model, but my guess is he doesn't expect us to be experts at that. I think understanding the two models and the experiments he talks about (like photoelectric effect experiment) is a good enough place to start. If we understand the models well, we can probab...
Thu Oct 10, 2019 12:11 am
Forum: Balancing Chemical Reactions
Topic: H.7 Catalysts [ENDORSED]
Replies: 4
Views: 259

### Re: H.7 Catalysts[ENDORSED]

Catalysts can work in a variety of ways. One way is as a reactant in an intermediate reaction. A lot of the chemical equations we see are simplified and don't include middle steps. An example is O3 + O --> 2O2. That reaction is catalyzed by Cl and in full it is actually two steps 1. Cl + O3 --> ClO ...
Wed Oct 09, 2019 11:54 pm
Forum: Empirical & Molecular Formulas
Topic: Naming Random Comounds
Replies: 3
Views: 87

### Re: Naming Random Comounds

Tin is a transition metal, and like most of the transition metals (Ag and Zn are the common exceptions, forming only 1+ and 2+ ions respectively), it can become differently charged ions. In particular, tin can either become Sn 2+ or Sn 4+. Therefore the compound has to be named Tin (IV) Oxide to tel...
Wed Oct 09, 2019 11:42 pm
Forum: Molarity, Solutions, Dilutions
Topic: G. 23
Replies: 3
Views: 119

### Re: G. 23

I'm not entirely sure what you were trying to multiply by 2, but I'm guessing you may be combining NaCl and KCl too early in your calculations. You can't add the masses together and divide by a combined molar mass and then multiply by 2, and you can't just find the # of moles of one of the compounds...
Sat Oct 05, 2019 12:34 am
Forum: Empirical & Molecular Formulas
Topic: Empirical and Molecular Formulas
Replies: 2
Views: 84

### Re: M. 19

Yeah, nitrogen is diatomic so it rarely is seen as just "N." It is usually N2 gas, but that isn't very relevant for finding the empirical and molecular formulas (just for writing the balanced equation). To find the empirical formula, you can start by calculating how many moles of CO2 were ...
Fri Oct 04, 2019 11:47 pm
Forum: Molarity, Solutions, Dilutions
Topic: G23
Replies: 2
Views: 85

### Re: G23

I agree with the above commenter. You just need to find how many moles of NaCl and KCl were added by dividing each compound by its respective molar mass. Then, since the ratio is 1:1 (cation : Cl-) in both compounds, the number of moles of compound = the number of moles of Cl- in each. To find the t...
Tue Oct 01, 2019 9:29 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Naming Compounds (F13)
Replies: 7
Views: 145

### Re: Naming Compounds (F13)

In both ionic and molecular compounds, the ending of the second element is changed to -ide. In ionic compounds, the second element is the one that acts as an anion. Generally in molecular compounds, the element further to the right on the periodic table is the second one. So, in this case, chlorine ...
Tue Oct 01, 2019 8:45 pm
Forum: Significant Figures
Topic: How Many significant figures to use ?
Replies: 9
Views: 214

### Re: How Many significant figures to use ?

To add on to what the others said, it is true you can generally base your answer off of the smallest number of sig figs in the original numbers. However, you have to be careful not to count definitions like metric conversion factors (as mentioned) or numbers that could have been garnered from counti...
Mon Sep 30, 2019 8:29 pm
Forum: Significant Figures
Topic: Constants and Sig Figs
Replies: 4
Views: 83

### Re: Constants and Sig Figs

I think that yes, the answer would be limited to 4 sig figs. The molar mass of carbon is an imprecise, rounded measurement (that's why it could also be considered 12.011 g/mol). Unlike, exact definitions (e.g 1000 mL = 1 L) or counted numbers (e.g 4 beakers), the sig figs of all measurements must be...