Search found 48 matches

by Jovian Cheung 1K
Sun Dec 09, 2018 1:12 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Calculating change in pH after dilution [ENDORSED]
Replies: 2
Views: 110

Re: Calculating change in pH after dilution [ENDORSED]

Since pH = -log [H+] of a given solution, we can set pH old = -log [H+]old and pH new = -log [H+] new. From the wording of the problem, we know that [H+]new = [H+]old*0.12. As a result, if you take the -log of both sides of the equation, pH new = pH old + (-log 0.12) (keep in mind the rule log (A*B...
by Jovian Cheung 1K
Sat Dec 08, 2018 3:22 pm
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sundays 4-6pm (Karen) [ENDORSED]
Replies: 135
Views: 28297

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sundays 4-6pm (Karen) [ENDORSED]

For the tail itself, you need to think about it when it's removed from the Co, so break the bond and give it its respective lone pairs, the charge should be 0 + 0 + 0 +0 + -1 = -1. For the N with formal charge -1, can you please explain why is it -1 instead of +1? When it's removed from the Co, it ...
by Jovian Cheung 1K
Sat Dec 08, 2018 2:31 pm
Forum: Bronsted Acids & Bases
Topic: Metal oxides and non-metal oxides
Replies: 1
Views: 59

Metal oxides and non-metal oxides

I know that metal oxides form bases in water and non-metal oxides form acids in water, but how do we judge whether they are strong or weak? Many thanks!
by Jovian Cheung 1K
Fri Dec 07, 2018 11:09 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: number 38 of the churro practice exam
Replies: 1
Views: 112

Re: number 38 of the churro practice exam

S and Se are both in group 6 and have the same number of valence electrons. So their VSEPR shapes are essentially the same! Both are bent, polar and have dipole-dipole interactions (as well as LDF). Then, as Se is larger in size than S, this strengthens the LDF and gives it a higher boiling point. I...
by Jovian Cheung 1K
Fri Dec 07, 2018 10:48 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Calculating change in pH after dilution [ENDORSED]
Replies: 2
Views: 110

Calculating change in pH after dilution [ENDORSED]

Regarding the textbook (6th edition) question 12.19... The question is: The concentration of HCl in hydrochloric acid is reduced to 12% of its initial value by dilution. What is the decrease in the pH values of the two solutions? The solution is: HCl is a strong acid. If concentration decreases to 1...
by Jovian Cheung 1K
Fri Dec 07, 2018 10:39 pm
Forum: Lewis Structures
Topic: Lewis structure of sulfur dioxide
Replies: 1
Views: 162

Lewis structure of sulfur dioxide

In the 6th edition textbook question 12.15, the Lewis structure of SO 2 as a Lewis acid is asked for. Why can't the S form double bonds with both oxygens? It should be able to expand its octet. Is it because the molecule is stable when the formal charges are dispersed on the non-central atoms (i.e. ...
by Jovian Cheung 1K
Fri Nov 30, 2018 8:37 pm
Forum: Hybridization
Topic: Determining Factors
Replies: 3
Views: 70

Re: Determining Factors

It is based on the number of electron domains (in 14A I think they’re called regions of electron densities, per the previous post!) :-) Put simply, one electron domain/region of electron density can be: - a lone pair - bonds (multiple bonds are counted as one domain) Please correct me if there’s any...
by Jovian Cheung 1K
Fri Nov 30, 2018 8:34 pm
Forum: Lewis Acids & Bases
Topic: Mixing up Lewis and Bronsted
Replies: 3
Views: 80

Re: Mixing up Lewis and Bronsted

Note that protons are equivalent as H+ ions! The Bronsted Lowry definition is more restrictive as it specifies the exchange of hydrogen ions. The Lewis definition, on the other hand, is more general because it doesn’t specify the substance and only specifies that there needs to be an electron pair e...
by Jovian Cheung 1K
Fri Nov 30, 2018 8:26 pm
Forum: Dipole Moments
Topic: Induced Dipole - Induced Dipole
Replies: 3
Views: 114

Re: Induced Dipole - Induced Dipole

Induced dipole-induced dipole is the same as London / dispersion forces :-)
by Jovian Cheung 1K
Fri Nov 16, 2018 5:40 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Single Regions?
Replies: 8
Views: 157

Re: Single Regions?

Are single regions = electron domains?

Since in high school, I learnt that each bond pair OR lone pair is classified as a single electron domain.

Many thanks! (Hope this isn't hijacking the thread, just hoping that it would add to the discussion!) :-)
by Jovian Cheung 1K
Fri Nov 16, 2018 5:36 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Octahedral
Replies: 4
Views: 73

Re: Octahedral

For 6 electron pairs: Octahedral: AX6 Square pyramidal: AX5E Square planar: AX4E2 Just to clarify a bit more for the OP, these 3 molecular shapes (octahedral, square pyramidal, square planar) all have the electron domain arrangement/configuration 'octahedral'. But only AX6 has both octahedral elect...
by Jovian Cheung 1K
Fri Nov 16, 2018 5:34 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: cis and trans prefix's to molecules
Replies: 2
Views: 48

Re: cis and trans prefix's to molecules

Double bonds prevent rotation. So imagine a molecule like C 2 H 2 Cl 2 (search up the structure and you'll see images of the isomers, including the cis and trans ones), where the two C are double bonded and there is one Cl and one H on each C. The isomer where both Cl are on the same side is the cis...
by Jovian Cheung 1K
Fri Nov 16, 2018 5:27 pm
Forum: Resonance Structures
Topic: Resonance Structures
Replies: 6
Views: 184

Re: Resonance Structures

That makes so much more sense! thank you! Also note that in the "real" structure (in the real world), the molecule's bonds would be an actual blend of the bonds involved in the resonance structures! So their bond lengths etc. would also be the average. (E.g. the midterm question on resona...
by Jovian Cheung 1K
Fri Nov 16, 2018 5:23 pm
Forum: Resonance Structures
Topic: Resonance Structures
Replies: 6
Views: 184

Re: Resonance Structures

I was wondering if for resonance structures do you need to have the same element of atom surrounding the central atom? And can there be more than one double bond for resonance to occur? For Q1, I'd like for someone to answer this too. So far, I've never come upon a case where I have to consider pla...
by Jovian Cheung 1K
Fri Nov 09, 2018 12:57 pm
Forum: Quantum Numbers and The H-Atom
Topic: Test Quantum Numbers
Replies: 4
Views: 125

Re: Test Quantum Numbers

l = 1 tells us that it's referring to a p-orbital. Any p-orbital would only be able to hold 6 electrons :)
by Jovian Cheung 1K
Fri Nov 09, 2018 12:55 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: Boiling point
Replies: 12
Views: 238

Re: Boiling point

Rod-shaped and spherical-shaped are used to describe the shape of the molecule. Since rod-shaped/longer molecules have more contact surface area when packed together --> more surface for intermolecular forces and attractions, they tend to have a higher boiling point. Spherical-shaped molecules don't...
by Jovian Cheung 1K
Fri Nov 09, 2018 12:52 pm
Forum: Octet Exceptions
Topic: Octet vs formal charge
Replies: 16
Views: 446

Re: Octet vs formal charge

It's actually hard to say which is more important. Just reduce the formal charges to as close to zero as you can WHILE still abiding restrictions related to the octet rule. If the atoms can be an exception to the octet rule (like phosphorus which can expand its octet), then prioritise formal charges...
by Jovian Cheung 1K
Fri Nov 09, 2018 12:42 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Trigonal Planar
Replies: 8
Views: 112

Re: Trigonal Planar

It's 2D in the sense that yes, the atoms are on the same plane. But it's a molecule, so it's still 3D, like how a piece of paper is 3D.

:)
by Jovian Cheung 1K
Fri Nov 09, 2018 12:39 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Valence Electrons - Are electrons in the d orbitals considered valence?
Replies: 3
Views: 237

Re: Valence Electrons - Are electrons in the d orbitals considered valence?

I also was wondering how do you find the valence electrons for elements in the d orbitals? Usually only the electrons in the highest energy level are counted as being valence, but for transition metals, the d-orbital electrons after the previous noble gas configuration count too. For example, for F...
by Jovian Cheung 1K
Sat Nov 03, 2018 4:28 pm
Forum: Lewis Structures
Topic: Drawing ClO4-
Replies: 1
Views: 65

Drawing ClO4-

Regarding the GarlicBread exercise Q12(b), What are your rationales when drawing the lowest energy Lewis structure for ClO 4 - ? The Cl expanded its octet. When do we know whether we need to draw a structure with an expanded octet? As seen in this video, (https://www.youtube.com/watch?v=bXEMU2fMMus)...
by Jovian Cheung 1K
Fri Nov 02, 2018 10:22 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Valence Electrons - Are electrons in the d orbitals considered valence?
Replies: 3
Views: 237

Re: Valence Electrons - Are electrons in the d orbitals considered valence?

For s and p block elements, they are not counted. (https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=417) For d block elements (which can use their d orbital electrons for bonding), they are counted. (https://socratic.org/questions/how-do-you-calculate-the-number-of-valence-electrons-in-an-atom) <...
by Jovian Cheung 1K
Fri Nov 02, 2018 10:11 pm
Forum: Coordinate Covalent Bonds
Topic: Tetrafluoroborate anion
Replies: 3
Views: 266

Re: Tetrafluoroborate anion

Going off of this question, why does the boron trifluoride atom not form a coordinate covalent bond with the fluorine to get an octet opposed to adding an additional fluorine atom? I think this is exactly what it does to form BF 4 - , where one of the F donates a pair of electrons to B. But as F on...
by Jovian Cheung 1K
Fri Nov 02, 2018 10:09 pm
Forum: Lewis Structures
Topic: How does nitrogen form 4 bonds?
Replies: 3
Views: 159

Re: How does nitrogen form 4 bonds?

Ok, thank you!
So I guess there is definitely a coordinate bond whenever we see nitrogen forming 4 bonds.
by Jovian Cheung 1K
Fri Nov 02, 2018 12:54 am
Forum: Lewis Structures
Topic: How does nitrogen form 4 bonds?
Replies: 3
Views: 159

How does nitrogen form 4 bonds?

As in the question. Can't imagine any other way than a coordinate bond. Thank you! :-)
by Jovian Cheung 1K
Wed Oct 31, 2018 8:23 pm
Forum: Coordinate Covalent Bonds
Topic: Tetrafluoroborate anion
Replies: 3
Views: 266

Tetrafluoroborate anion

Today it was mentioned that boron forms the tetrafluoroborate anion (BF 4 - ) with fluorine, provided that there is a coordinate bond. Yet when I search up the structure of BF 4 - online, none of the images contain an arrow between boron and fluorine. Would someone mind explaining this to me please?...
by Jovian Cheung 1K
Wed Oct 24, 2018 10:41 pm
Forum: Sigma & Pi Bonds
Topic: 3.9 (sixth edition)
Replies: 1
Views: 113

Re: 3.9 (sixth edition)

Note that for all these metal ions, the two 4s 2 electrons have been removed to form the M 2+ ions. Thus if you put the two 4s electrons back into the configuration, it would be the configuration of the original metal M. E.g. for [Ar]3d 6 , the original configuration of the metal atom would be [Ar]3...
by Jovian Cheung 1K
Wed Oct 24, 2018 10:36 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron configurations
Replies: 2
Views: 68

Re: Electron configurations

Do you mean the [Ar]4s13d5 kind of shorthand? :-)
by Jovian Cheung 1K
Wed Oct 24, 2018 10:34 pm
Forum: Trends in The Periodic Table
Topic: Isoeletronic
Replies: 3
Views: 95

Re: Isoeletronic

For example, Cl (which has 17 electrons) gains one electron to form Cl - (which has 18 electrons). Notice that Ar, a noble gas, also has 18 electrons. There are many many such examples! :-) To be fair, an atom of an element won't have the same number of electrons as its own ion(s). It can, however, ...
by Jovian Cheung 1K
Fri Oct 19, 2018 5:35 pm
Forum: DeBroglie Equation
Topic: Wave properties of large particles
Replies: 3
Views: 81

Wave properties of large particles

According to the DeBroglie Equation, wave properties of large particles like baseballs do exist, but are just undetectable (please let me know if I'm wrong). But what do these wave properties mean in a literal sense? A baseball doesn't move like a wave (even if it's undetectable), so what specific p...
by Jovian Cheung 1K
Fri Oct 19, 2018 2:52 pm
Forum: DeBroglie Equation
Topic: Wavelength unit conversion
Replies: 4
Views: 83

Re: Wavelength unit conversion

1 joule = 1 kg•m2•s-2 in SI units! :o)
by Jovian Cheung 1K
Mon Oct 15, 2018 12:12 am
Forum: Properties of Electrons
Topic: Energy Levels
Replies: 4
Views: 269

Re: Energy Levels

It has to do with the effective nuclear charge. Shielding also plays a factor. The shielding effect describes the balance between the pull of the protons on valence electrons and the repulsion forces from inner electrons. The effective nuclear charge is the net positive charge experienced by valenc...
by Jovian Cheung 1K
Fri Oct 12, 2018 7:46 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Post-Mod Assessment #40
Replies: 4
Views: 76

Re: Post-Mod Assessment #40

I think the answer I got is approximately C. The difference could be due to the sig.figs. and constants. Perhaps try if that works?
by Jovian Cheung 1K
Fri Oct 12, 2018 5:31 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Post-Mod Assessment #40
Replies: 4
Views: 76

Re: Post-Mod Assessment #40

Image

These are my workings, please check if they're correct ty! :o)
by Jovian Cheung 1K
Fri Oct 12, 2018 5:24 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Post-Mod Assessment #40
Replies: 4
Views: 76

Re: Post-Mod Assessment #40

I'm trying to do it - what is the answer supposed to be?
by Jovian Cheung 1K
Fri Oct 12, 2018 5:07 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Deriving Formula for Wavelength
Replies: 2
Views: 41

Re: Deriving Formula for Wavelength

Image

Does it start like this? (I'm curious too) :o)
by Jovian Cheung 1K
Fri Oct 12, 2018 4:56 pm
Forum: Properties of Electrons
Topic: Energy Levels
Replies: 4
Views: 269

Re: Energy Levels

I've always been taught that the energy levels get closer and closer and eventually converge - just as a rule of thumb - but I'd like to know why too. As for the second question, calculate the E FINAL and E INITIAL for whichever two energy levels that you are transitioning between (respectively) by ...
by Jovian Cheung 1K
Fri Oct 05, 2018 1:15 pm
Forum: General Science Questions
Topic: Significant figures / decimal places in intermediate steps in calculations
Replies: 4
Views: 188

Re: Significant figures / decimal places in intermediate steps in calculations

Thinking of it, I usually used a lot of ellipses in high school, like 6.87345... to include more digits, but I'm not sure if that's still a valid presentation in college? :-) Many thanks!
by Jovian Cheung 1K
Fri Oct 05, 2018 12:12 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Molar Mass units
Replies: 2
Views: 56

Re: Molar Mass units

As x-1 = 1/x in a mathematical scenario
mol-1 = 1/mol
So actually g*mol-1 is the same as g/mol, which implies 'grams per mole' :-)
by Jovian Cheung 1K
Fri Oct 05, 2018 12:05 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Definition and Application of Moles
Replies: 2
Views: 55

Re: Definition and Application of Moles

The mole is essentially just a number used as a unit. I'm guessing: Atoms are tiny, so a small weighed mass of atoms would actually contain a large number of them. So the scientists wanted a unit that was a big number! The development/choosing of such a number is tricky, but somehow they decided to ...
by Jovian Cheung 1K
Thu Oct 04, 2018 11:53 pm
Forum: Balancing Chemical Reactions
Topic: Mole Coefficients in Chemical Equations
Replies: 6
Views: 276

Re: Mole Coefficients in Chemical Equations

While the numbers of moles for each element has to be equal, the numbers of moles for molecules etc. in general don't have to be equal on both sides. Part of the point of balancing is that no atoms spontaneously get created, and no atoms spontaneously disappear. But otherwise they can combine/split ...
by Jovian Cheung 1K
Thu Oct 04, 2018 11:40 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: writing the formula of a molecule
Replies: 5
Views: 244

Re: writing the formula of a molecule

Magnesium is Mg. It forms the ion Mg 2+ . Sulfate refers to the sulfate ion, which is a polyatomic ion with formula SO 4 2- . As their charges have the same absolute value, which is 2, their ratio in an ionic compound is 1:1. Thus Magnesium Sulfate is MgSO 4 . (As you see, the 2+ and 2- cancel each ...
by Jovian Cheung 1K
Thu Oct 04, 2018 11:29 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Moles and Molar Mass
Replies: 10
Views: 134

Re: Moles and Molar Mass

@Cecilia
Glad that you fixed it but was planning to say 1m is 10^12pm, not 10^-12pm; I think that's the only problem there, otherwise nothing's wrong with it! :-)
by Jovian Cheung 1K
Thu Oct 04, 2018 10:11 pm
Forum: General Science Questions
Topic: Significant figures / decimal places in intermediate steps in calculations
Replies: 4
Views: 188

Significant figures / decimal places in intermediate steps in calculations

If I do not complete all my calculations in one step, in how many sig.figs/d.p.s should I present my intermediate values?

Thanks a lot! :-)
by Jovian Cheung 1K
Wed Oct 03, 2018 10:15 pm
Forum: Balancing Chemical Reactions
Topic: Balance Equation L.35
Replies: 6
Views: 228

Re: Balance Equation L.35

Just checked the appendix. There seems to be three similar units: "tonne", abbreviated as "t", equivalent to 10^3 kg "ton" (short, US), abbreviated as "ton", equivalent to 901.184 74 kg (?) "ton" (long, UK), abbreviated as "ton", equivalent...
by Jovian Cheung 1K
Tue Oct 02, 2018 11:07 pm
Forum: Balancing Chemical Reactions
Topic: Balance Equation L.35
Replies: 6
Views: 228

Re: Balance Equation L.35

Here's the rest of the steps, after each equation has been balanced. This is sort of extended and drawn-out, which is hopefully easy to follow, but there may be a faster way. I think Christine's method that she mentioned above would be a good workaround to get the solution while skipping the unneces...
by Jovian Cheung 1K
Tue Oct 02, 2018 10:41 pm
Forum: Balancing Chemical Reactions
Topic: Balance Equation L.35
Replies: 6
Views: 228

Re: Balance Equation L.35

Regarding how to balance the third equation :o)

Image

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