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| Q&A
for 20A-1 |
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When calculating the maximum number of electrons after being givin a set of quantum numbers (ex n = 4, l = 2, ml = +1), in what order should the d-orbitals be set up to find which one corresponds to ml +1? Is it dxy, dxz, dyz, dx2-y2, dz2 or is there another order I did not find?
conventionally we start the p and d orbitals and any others with minus values. so for d we have -2, -1, 0, 1, 2 Actually dz2 corresponds to 0 but dont worry about this correspondence since it is not 1 to 1 anyway. Some of the orbitals are a combination of two values of m sub l. e.s.
What is the difference between a chelate and a bidentate?
yes the chelate is the compound formed. Bidentate ligands are one way of forming such compounds. e.s.
I've been going over the different models of the atom, and I'm confused by the improvements of Bohr's model. I understand how the existance of discrete orbitals explains the quantization of the emmision spectrum, but not how it solves the problem of the rotating (and therefore accelerating) electron radiating energy and eventually crashing into the nucleus. The book describes the Bohr orbits as "sationary and nonradiating" but if the electron is still orbiting (rotating), even at a constant radius, shouldn't still emit energy? I hope my question makes sense, and thanks in advance for your reply.
The resaolution of the stability issue is not entirely satisfactory in the Bohr model. Bohr just stipulates that there is no radiation contrary to expectations from classical mechanics, except in cases of a transition between quantum levels. e.s.
Hi, I have few questions: 1. Is there other ways to determine if a ligand has high or low spin other than memorize the the spectrochemical series on page 291 of reader? 2. when a question ask if the hydrogen groups in a compound are magnetically equivalent, do we just examine if they having the same electron pairs? 3. In determine how many peaks occur in the NMR spectrum dur to chemical shift, do we just count the number of distinct hydrogen groups? 4. What kind of info do we need to remember about color wheel? Wavelength of absorption or complementary colors? Thanks
no other way.
Do we need to know the nomenclature of hydrocarbon for the final?
No
Is organic chem part of the final too? They are not on the sample final.
yes it is.
When enrolling for chem 20b and the lab, they both show that I do not have the proper prerequisites. I am in your 20a and I would like to know what I need to do to be admitted into the class.
Please ask this question to the folks in the undergrad chem office. Young 4009
This might be a little too late, but for the Mastering Chemistry Quiz on Formula and Structure, there is one problem that just displays a molecule and has no follow up instructions. The answer for this question is a five digit combination of 0 and 1 (i.e. 0,1,1,0,0) I am wondering what these numbers mean.
I will try to check. The best thing is to send a message to Marek. See web pages for his E-mail. Tell him about this problem. e.s.
One of the TA mentioned that we are able to see our mid term grade in MYUCLA website, but when i click the "grade" for Chem 20A, it says something like this function is not activated yet. I am just wondering if it is the problem of my MYUCLA account, or the mid term grade stil does not post on it yet.
NO, WE ARE NOT USING THIS FUNCTION IN THIS COURSE. The TA was incorrect. E.S.
The example we did today in class to identify the hybrid orbit in H-C(3bond)C-C=C, here I ignored some H. You said the third C is sp^2 orbit since is has a double bond with the last C, but it also has a single bond with the 2nd C, why isn't sp^3 ? Why do we prefer to consider one bond over another? Another, Just want to make sure that problem 4 in sample midtern can be ignored for Wed exam, right? Thanks
The simultaneous presence of single and double bonds implies sp2. The single bonds are due to the hybrid orbitals while the double bond is actually due to unhyb' orbitals if you recall. It is not a case of the double bond taking precedence! e.s.
Is there any way to obtain the keys for the posted and emailed sample midterms? It would be very helpful for studying purposes to be able to check our answers.
We will organize this. e.s.
Hi Dr. Scerri does Cerium have a 6s24f1 configuration or a 6s25d1 configuration? Your notes say that from lanthanum on, f-orbitals begin to fill, while the book says that lanthanum has a 6s25d1 configuration. Thank You in advance.
You are supposed to give the 'expected configuration' according to the n+l rule or the aufbau diagram. This means that Ce would have f electrons as the differentiating electrons. The full story is more complicated. If you look on my web page there is an article I wrote called, Chemistry, Spectroscopy and the Question of Reduction. This looks at the configurations of rare earths in detail. Published in Journal of Chemical Education. e.s.
Dr. Scerri, for writing the electron configuration the book uses (pi_2p)^4 for example, but in mastering chemistry, it is given as (pi_2px)^2(pi_2py)^2, which one would you preffer to be used on the test? Thank You
The second way e.s.
Hello, in Chapter 13, Homework question #75 (b), isn't ICL3 supposed to have a trigonal planar molecular structure? The solution for 75 (b) says that it is T-shaped and the bond angles are 90 degrees. Thanks
The book is correct. The molecule is like ClF3. There are 2 lone pairs on the central atom which prevents it from being trigonal planar. See p. 193 and 195 of reader. e.s.
The book touches upon a controversey between whether filling an octet or minimizing formal charge is preferred. For this class, which structure would be preferred? For instance, SO2 can be written with an S with two double bonds (exceeding the octet rule, but minimizing formal charge) or it can be written as an S with a single bond and a double bond (obeying the octet rule, but not minimizing formal charge). Thanks in advance, Dr. Scerri.
Obeying the octet rule should be given preference for the sake of giving a general rule for this course. But as you and the textbook mentions it's more complicated. e.s.
I have a question regarding the hybridization of atoms arounds a central atom. In our chemistry book, it states that we can assume the Cl atoms to have a hybridization of sp3 in a CCl4 molecule. However, in Mastering Chemistry, we are taught that ligands do not need to be hybridized in order to form bonds with the central atom. Both of these claims make sense in terms of CCl4. According to the book, with Cl4 hybridized at sp3, one sp3 orbital is used to form to covalent bond with C and the other three are used for the three lone pairs. Adhering to Mastering Chemistry, a p orbital would be used to form the covalent bond with the central atom, leaving the two remaining p orbitals and the s orbital to hold lone pairs. Which of these two claims should we follow?
It can be done both ways. For exam purposes follow the Mastering chem version. Hybridization occurs just on the central atom. e.s.
I would like to know the cut-off for MT2 in terms of the page number on the reader. Also, will nodes for different orbital and representation of wavefunction on MT 2?
The cut off will be where we get to at the end of Mondays class! No nodes were already examined in mid term 1
There were questions in Mastering Chemistry that goes something like this: Spell the name of an element that has a ns^0(n-1)d^5 electron configuration for its +2 ion. I was just confused about the s^0 part. I notice that it's a +2 ion but does that mean Manganese and its group all ionize their s electrons first, or are they exceptions? Thanks in advance.
As mentioned several times in lectures ALL transition metals, not just the manganese group, ionize their s electrons first. e.s.
Will the first midterm be curved? if so when or how can we see our final grade
Yes but grades will not be assigned for mid terms. You are just given the average and SD so that you can form some idea of where you stand.
Hi professor Scerri, I have a question about the electron configuration of Cr+. I know that it is one of two elements in the 3d subshell that is an exception. But since it is ionized, does it have the configuration equal to that of Vanadium or is it [Ar]4s1 3d4? thank you.
Perhaps you mean WHEN it is ionized, since it does not have to be! The Cr ion loses electrons from the 4s preferentially. So Cr+1 would be [Ar]3d5 and so on. None of this is relevant to mid term 1. e.s.
Should we know the names of all the people that were mentioned in Chapter 12 and their contribution to chemistry and the periodic table?
To some extent, but you will not be asked such point blank questions as what was the rutherford model, although you may be asked things about it. e.s.
This is more of a "call to your attention" than a question. I'm not really worried about this one point, so don't worry about it, but your online quizes aren't always right. For one answer on the last quiz i put 13G/10 and got it incorrect becaues the answer was 1.30 G. That one point isn't going to make or break my grade, but if I lose a couple questions on each quiz like that, then it will. Please try to fix it or give me a tip to avoid the same thing happening again. Thanks.
There are a few, very few, glitches like this on Mastering Chemistry. We have alerted the people at UC Fullerton who run the system but will remind them again. THis should not be on on-going problem. e.s.
I'm currently working through the material regarding the electron filling (Chapter 12). Would it be profitable to memorize the various rules and exceptions for electron configuration?
No but you should know just the first two exceptions Cr and Cu and what their configurations are, namely they have 4s1 3d5 and 4s1 3d10 respectively. In any case I am not sure we will get this far during Monday's class!
On the syllabus, there is a reading that includes 12.6. Is this a mistake or do we really need to understand this section? Thank you in advance for answering my question.
No this is a mistake. Ignore particle in a box. e.s.
Dear Dr. Scerri: Although I have looked thoroughly at the course website for Chem 20A, I have unfortunately not found the due dates for the "Mastering Chemistry" quizzes. Do you know where I might find these? Additionally, how are we to know what to study for the quiz? I look forward to hearing from you at your earliest convenience. Best regards, Chase Laurelle Knowles
The info should be posted. As I said before ALL questions on this should go to "Marek Grzeskowiak"
Is there any reading that you recommend before we start class in the fall?
Nothing specific but here are some general suggestions.
Try to find your chemistry notes from previous courses.
This will allow for comparison and continuity.
Familiarize yourself with the textbook.
Start reading the course reader.
e.s.
Question:
Date Submitted: Sat Sep 24 10:33:06 US/Pacific 2005
Student Name: Gail
Student Email: igsa04@yahoo.com
Submitted from:
Answer:
Questions? Comments?
Please send to voh@chem.ucla.edu
Last revision: June 28, 2005