CHEMISTRY COMMUNITY

Jovian Cheung 1K

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...

Jovian Cheung 1K

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 ...

Jovian Cheung 1K

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!

Jovian Cheung 1K

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...

Jovian Cheung 1K

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...

Jovian Cheung 1K

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. ...

Jovian Cheung 1K

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...

Jovian Cheung 1K

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...

Jovian Cheung 1K

Induced dipole-induced dipole is the same as London / dispersion forces :-)

Jovian Cheung 1K

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!) :-)

Jovian Cheung 1K

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...

Jovian Cheung 1K

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...

Jovian Cheung 1K

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...

Jovian Cheung 1K

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...

Jovian Cheung 1K

l = 1 tells us that it's referring to a p-orbital. Any p-orbital would only be able to hold 6 electrons :)

Jovian Cheung 1K

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...

Jovian Cheung 1K

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...

Jovian Cheung 1K

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.

:)

Jovian Cheung 1K

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...

Jovian Cheung 1K

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)...

Jovian Cheung 1K

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) <...

Jovian Cheung 1K

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...

Jovian Cheung 1K

Ok, thank you!
So I guess there is definitely a coordinate bond whenever we see nitrogen forming 4 bonds.

Jovian Cheung 1K

As in the question. Can't imagine any other way than a coordinate bond. Thank you! :-)

Jovian Cheung 1K

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?...

Jovian Cheung 1K

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...

Jovian Cheung 1K

Do you mean the [Ar]4s¹3d⁵ kind of shorthand? :-)

Jovian Cheung 1K

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, ...

Jovian Cheung 1K

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...

Jovian Cheung 1K

1 joule = 1 kg•m²•s^-2 in SI units! :o)

Jovian Cheung 1K

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...

Jovian Cheung 1K

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?

Jovian Cheung 1K

These are my workings, please check if they're correct ty! :o)

Jovian Cheung 1K

I'm trying to do it - what is the answer supposed to be?

Jovian Cheung 1K

Does it start like this? (I'm curious too) :o)

Jovian Cheung 1K

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 ...

Jovian Cheung 1K

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!

Jovian Cheung 1K

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' :-)

Jovian Cheung 1K

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 ...

Jovian Cheung 1K

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 ...

Jovian Cheung 1K

The quick answer is that 1.001 has 4 sig figs :0)

http://chemistry.bd.psu.edu/jircitano/sigfigs.html

http://chemcollective.org/activities/tu ... nt_figures

Jovian Cheung 1K

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 ...

Jovian Cheung 1K

@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! :-)

Jovian Cheung 1K

Alright, thank you very much!

Jovian Cheung 1K

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! :-)

Jovian Cheung 1K

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...

Jovian Cheung 1K

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...

Jovian Cheung 1K

Regarding how to balance the third equation :o)

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