This Blog is to answer general questions about the lecture section of Chem 101 (Section A02). Enter your question in the comments and I will reply within the comments as well. As no identification is required to post, the blog is moderated (to reduce spam) so comments will not appear immediately but should be posted with a reply within 24 hours. Feel free to look over other people's comments and chime in.
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Question from email
ReplyDelete"When trying to find the wavelength of and atom or molecule using de Brolie's equation, how do you determine the mass of the atom or molecule? For example, one of the textbook questions asks for the
wavelength of a lithium atom, and I don't seem to get the right answer using the atomic mass. Thanks."
Atomic mass is mass of a mole of lithium (6.02*10^23 atoms). The atomic mass divided by Avogadro's number will give you the weight of a single atom of lithium.
ReplyDeletequestion from email
ReplyDelete"for the midtern I'm just wondering if we need to now the names of people and who they are, what they do... history and such thats in the textbook ..
like Plank, Einstein, Bohr, Rydberg, Louis de Brogile, Heinsenberg, Schrodinger ... or just whatever is in the blackboard notes is whats
important?"
1) We will not be testing the history directly. However, you should be aware of the names when tied to what they studied. ie: the Bohr model of the atom, Heisenberg's uncertainty principle etc..
ReplyDelete2) Basically, everyting in the assigned readings/assignments is testable (with minor exceptions ie the date Bohr got his Nobel Prize). The notes should highlight the important parts and cover about 80% of the material.
I've been having a hard time learning how to properly write electron configurations for atoms. Any tips on how i could better grasp this idea, and understand the concept?? It seems to be very important to the overall chemistry course.
ReplyDeleteFor a start, you are entirely correct that electron configurations are important and we will build on this concept. Also, I want to clarify that electron configurations only need to be produced from scratch up to the 5s orbital. Everything after that is too complicated for you to produce.
ReplyDeleteBefore 5s, the only oddities are Cr and Cu. After that there are lots of oddities. I suggest starting with the periodic table and write out the electron configuration for each element. H, He, Li etc... Write it out in full until you get really, really bored and then start adding in the noble gas configuration in to save yourself from finger cramps.
Finally, you may notice some oddities with the 4s and 3d orbital energies flippng in energy/order. Either order is allowed. The reletive energies are very close and the final energy depends on whether you are filling or emptying the orbitals.
Hope that helps.
Also, there is a turorial linked from Prof Codding's page on orbital filling:
ReplyDeletehttp://www.wwnorton.com/college/chemistry/gilbert2/tutorials/interface.asp?chapter=chapter_07&folder=orbital_filling
Are the first and second quizzes due midnight October 2 or midnight October 3?
ReplyDeleteYou have 26 hours left- the quizzes are due midnight Oct 3 (and Quiz 3 will be due midnight Oct 5)
ReplyDeleteI'm still very lost about Zeff. I know that Z is the number of protons but I don't know how to calculate S. And why is it that you used 0.3 and 1 in your calculations but other before you did not?
ReplyDeleteAlso, do we need to kno slater's rules?
ReplyDeleteS is the shielding of all other electrons on the electron of interest. This value will always be LESS than the total number of electrons (whereas Z is always EXACTLY the number of protons).
ReplyDeleteCore electrons will shield for a value close to one (but slightly less) whereas valence electrons shield one another less effectively (about 0.3).
The reason I used actual values was to give a real number as an example, rather than saying valence electrons shield for "a value much lower than one".
There are a couple examples of calculations with Slater's rules in the assignments, but you would not need to memorise the values for Slater's rules (ie 0.3) calculate shielding using Slater's rules
You should be aware of the reasoning behind Slater's rules (ie core versus valance), but you don't need to know the specific rules (0.3 for a valence 1s, 0.35 for a valence 3s etc...)
ReplyDeleteHi Dr Sirk,
ReplyDeleteIn an iclicker question, "What determines the effective nuclear charge (Zeff)on a valence electron?" the answer was C and discluded distance as an answer. In the textbook (p266) it says in reference to ionization energies: "The large increase (in ionization energy) occurs because the 2p electron is much more likely to be found closer to the nucleus and therefore the 2p electron experiences a greater effective nuclear charge than 3s and 3p electrons" -- so does distance from the nucleus effect Zeff?
Excellent question: What you have found through careful reading is a somewhat subtle point and some sloppy writing within the text. What it should say is "The large increase (in ionization energy) occurs because the 2p electron is much more likely to be found closer to the nucleus and therefore the 2p electron experiences a greater attraction to the nucleus (proportional to effective nuclear charge/distance) than 3s and 3p electrons"
ReplyDeleteFrom the email vaults
ReplyDeleteHello Dr. Sirk,
I saw that the marks were up for Quizzes 1 and 2, however, I was
curious as to if there was a way to view which questions I got wrong,
for study purposes?
Thank you in advance,
Hello,
ReplyDeleteTHere is no specific way to view your quiz, but the answer keys are available here:
http://web.uvic.ca/~chem101/quizzes.html
You could also screen capture or print your quiz as you write to keep a copy. Just keeping the answers wouldn't work, as the order is randomised.
From the email vaults
ReplyDeleteHi Dr. Sirk,
I just have a couple of questions. First, do we need to learn sections
7.6-7.8 in the textbook? Second, would we be required to write the
electron configuration of an f orbital atom? For example, the textbook
question 7.47 e) asks you to write the electron configuration of Hg^+2.
If so, do you think you could show me how to write the configuration
for both Hg and Hg^+2? I'm unsure in what order the electrons are
removed once the f orbitals are involved.
Thanks!
1) Nope. The readings are listed with the assignments.
ReplyDeletehttp://web.uvic.ca/~chem101/assignments.html
The are also listed on the overview http://web.uvic.ca/~asirk/overview.htm
but the main Chem 101 page is the final authority.
2)For this question, use the figure on page 242. Once the f orbitals are involved things get a little wonky. You should be able to produce any electron configuration up to 5s2 (so only Cu and Cr are slightly different before that).
You should also know that the 4f follows the 6s (from the periodic table) Beyond that, the filling is beyond the scope of the course.
Hi Dr. Sirk,
ReplyDeleteI was wondering if you could specify exactly which units and which sections will be on the midterm?
The final decision has not been made yet, but will include Chapter 6 (6.1-6.9) and Chapter 7 (7.1-7.5) as well as some of Chapter 8 (8.1- not later than 8.5).
ReplyDeleteHi Dr. Sirk,
ReplyDeleteI also just had a couple of questions about the midterm. I know you said the final decision hasn't been made yet, but just wondering if there are going to be both multiple choice questions and a written portion? Also, do you know yet approximately how may questions there will be? Thanks.
I don't really know how to use blogspot, but in response to the person who asked if there was a way to view the quizzes after they are graded to see which questions you got wrong, you can do that. Once you log into blackboard and click on chem 101, click assessments on the sidebar. Then pick the quiz you want to look at. Click the square with the downwards arrow next to the title and click view submission. I'm not sure if it indicates what the right answer is or not... but I'm pretty sure the check box just indicates that's your answer, not that it's the right one.
ReplyDeleteThe format of the test will be similiar to previous midterms. See one example here (also posted on Chem 101 webpage):
ReplyDeletehttp://web.uvic.ca/~chem101/C101Midterm1A2009.print.pdf
and answer key
http://web.uvic.ca/~chem101/C101Midterm1A2009.key.pdf
So there will likely be 50 points with half multiple choice, half short answer. Note the multiple choice questions are 2 marks each.
And Thank-you for the quiz discussion.
ReplyDeleteHi Dr. Sirk,
ReplyDeleteI was wondering on Quiz 3, Question 5, why the answer was KF. Would it relate to the distance between the radii of each compound? Also would the solution to the answer follow the general trend of atomic radius on the periodic table if that was the case? The question is:
Of the compounds below, ____ has the smallest ionic separation.
RbCl
KF
SrBr^2
RbF
K^2S
Thank you very much!
In regards to the midterm, do we need to know what the Born-Haber Cycle is?
ReplyDeleteIonic Seperation comment:
ReplyDeleteI don't have much to add as you have answered your own question. The ionic seperation (or distance between the ions) will be greatest for a compound with larger ions.
KF has the smallest cation and the smallest anion of the 5 choices and therefore the smallest seperation.
As a side note, ionic seperation measures the ions, but the trend would hold true if you considered the two atoms as well (Because the anion gets bigger and the cation gets smaller).
The Born-Haber cycle will not be on the midterm. The energy of salt formation( for our purposes) is simplified to the three main contributors: enthalpy of ionisation, electron affinity and lattice energy.
ReplyDeleteI'm confused about lattice energy. How does it 'drive' ionic bonding? I understand that lattice energy is the energy required to break up the ionic compound when it forms, which shows the stability of the solid, but how does that make up for the net positive enthalpy of the ionic reaction (ie. that Na + Cl requires 147kj/mol more energy than the electron affinity of Cl provides)?
ReplyDeleteFor lattice energy trends, how do you determine what d is for a compound such as MgF2? Would the lattice energy of MgF2 be less than that for MgO?
ReplyDeleteReplies have been added to the midterm post.
ReplyDeletehttp://chem101a02.blogspot.com/
I was just attempting the midterm sample and this question kind of stumped me and i was just wondering if you could explain to me why c is the right answer.
ReplyDeleteThe effective nuclear charge experienced by the valence electron of a sodium atom is:
A. 10< Zeff <11 B. 9< Zeff <10 C. 1< Zeff <2 D.0<Zeff <1 E.Zeff =0
Assume the core electrons shield for 1 each. Zeff =Z-S. Therefore, 11-10 is one. Shielding is not perfect and therfore Zeff is greater than one.
ReplyDelete(The true value is about 2.2 from Slater's rules)
Dr. Sirk,
ReplyDeleteYou mentioned 'dipole moments' but did not talk about the equation (ยต=Qr). Will we be tested on dipole moment-type questions? (i.e. calculate the effective charges on X and Y given the info: 1.78 D and 0.98 A in regard to the molecule XY)
Merci
Please see midterm comment and reply.
ReplyDeleteDear Professor Sirk,
ReplyDeleteFor the probability function analogy you gave us in our notes, it states that there is a higher probability of landing in an area further away from the center. Also in the figure there is a higher density of dots closer to the center. In the 11th edition of our text book it gives us a similar figure stating that, "the regions with a high density of dots correspond to relatively large values of psi2 and are therefore regions where there is a high probability of finding the electron.” Does this mean that there is a higher probability of finding an electron further away from the nucleus and that there is a higher density of electrons closer to the center?
Thank you
Something was mentioned in the Prep 101 session about the fact that the intensity of a light increases the number of electrons emitted from a metal surface in the photoelectric effect. I do not remember this being discussed in the notes, only that a higher frequency results in a higher kinetic energy of the emitted photon. Is the effect of intensity something we will need to know?
ReplyDeleteHi, for question 5 on quiz 5 it says "In the nitrite ion (NO2-), __________." and you have to fill the blank. There are two possible correct answers for this question(which are both given as possible answers) but it doesn't tell you whether it is talking about overall bonds or lewis structures of the nitrite ion! The two possible CORRECT answers are A) one bond is a double bond and the other is a single bond and D) both bonds are the same. How are you supposed to know which answer to choose?
ReplyDeleteQ and A reposted in midterm 2
ReplyDelete