CHEM1111 Q&A by Girish Lakhwani https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w en-us 2021-07-27 08:00:44 UTC 2023-03-15 08:13:08 UTC hello@padlet.com test: how is the weather girishlakhwani1 https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1672239618 Ans: brilliant]]> 2021-08-09 00:40:45 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1672239618 Are there Pre-lecture videos we need to watch and if so where are they? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1674739567 Answer: As I have said a few times, all lecture materials are organised week wise. Since you're in week 1, goto Week 1 link on CHEM1111 canvas homepage and you'll find all relevant info there.]]> 2021-08-11 00:27:23 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1674739567 overall hydrogen burning reaction: why are the 2 protons crossed out? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1674740693 Answer: It's a result of solving multiple chemical equations simultaneously. For example, if product formed in one reaction and consumed as reactants in other, they can be cancelled out while writing overall reaction that is the sum of two. Care should be taken that number of products and reactants match up. More in lecture 3]]> 2021-08-11 00:28:32 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1674740693 positrons: where are positrons found? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1674744474 Answer: You will find them in radioactive decay reactions.]]> 2021-08-11 00:32:12 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1674744474 Periodic table: Could you explain how to read Periodic table again? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1674757061 Answer: Periodic table is organised by placing elements in increment order of 1 of their atomic number, Z, i.e. Z = 1, 2, 3, 4 ... running left to right within a row and then top to bottom. ]]> 2021-08-11 00:44:54 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1674757061 Would different isotopes used in the same chemical reaction provide the same products? for example would using the different carbon isotopes in the same reaction produce the same products? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1674759232 Answer: Not necessarily. It would depend on what other products are formed in the reaction. Remember, equations need to be balanced.]]> 2021-08-11 00:47:00 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1674759232 what is a positron? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1674762993 Answer: its a subatomic particle with +1 charge]]> 2021-08-11 00:50:55 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1674762993 Nuclear transformation: So can any element be transformed into any other element as long as it's balanced? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1674768471 Answer: Not always, there are some guiding principles that we will study about in next few lectures. Nucleogenesis is formation of new elements and hydrogen burning is an example of it. Radioactive decay, on the other, hand is decay or unstable nuclide either to their isotopes or stable elements.

]]> 2021-08-11 00:55:11 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1674768471 What is Shiometry? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1674776106 Answer: Its spelled as Stoichiometry. Its the calculation of reactants and products in the chemical reaction]]> 2021-08-11 01:02:09 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1674776106 Will the final exam be open book or closed book? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676102602 Answer: I will answer to this in the next few weeks once I have had sufficient consultation with the Unit coordinator and our education committee. ]]> 2021-08-12 00:04:00 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676102602 Difference between proton and positron except for their mass difference https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676104169 Answer: Both are sub-atomic particle with positive charge. Proton is much heavier than positron. Positron is as light as an electron so considered massless for practical purposes. ]]> 2021-08-12 00:05:57 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676104169 Should we memorise the 3 hydrogen burning equations? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676108404 Answer: It's not required to remember them but if I gave you a partial filled chemical equation, you should be able to fill the remaining elements and balance the overall equation. We did some such examples in lecture 2 worksheet. ]]> 2021-08-12 00:11:00 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676108404 Overall hydrogen burning reaction https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676111078 What is the purpose of simplifying all 3 reactions?]]> 2021-08-12 00:13:59 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676111078 Is the protons not equal on both sides in the overall hydrogen burning reaction? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676113243 Answer: While both 1H and 1p symbols can be used represent Hydrogen nucleus, its worth noting that 1H atom has an electron but 1p doesn't. You'll note in the overall reaction that two electrons are also formed in the product to accompany two 1p.]]> 2021-08-12 00:16:27 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676113243 Do we need to memorise the life cycle of stars? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676122071 Answer: No. Check the learning outcomes on the last slide of each lecture to know what we expect you to be able to do after each lecture.]]> 2021-08-12 00:24:45 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676122071 Why is lithium skipped in the helium to the red giant section? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676123586 Answer: Lithium is indeed formed from nuclear reactions in stars but is a bit more nuanced that others (such as Hydrogen, Helium and Carbon) we discussed in the second lecture. ]]> 2021-08-12 00:26:08 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676123586 The cancellation of the equation is not clear. Could you please explain it again？ https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676127413 Answer: It's a result of solving multiple chemical equations simultaneously. For example, if product formed in one reaction and consumed as reactants in other, they can be cancelled out while writing overall reaction that is the sum of two. Care should be taken that number of products and reactants match up.]]> 2021-08-12 00:29:52 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676127413 If an exponential curve never reaches 0 does that mean the amount of unstable nuclei continually gets smaller but does not completely decay to stable species? Or are the amounts so small that they're considered negligible? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676136508 Answer: The exponential curve continues indefinitely and is asymptotic as it approaches Y=0. This means that not all of the initial nuclei decay completely. There will always be a few nuclei (likely negligible) left behind at any time.]]> 2021-08-12 00:38:33 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676136508 Is there an official way of writing 2,3,4 etc half lives? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676142311 Answer: Half life is written as t1/2. You can write the rest as 2 t1/2, 3 t1/2, 4 t1/2]]> 2021-08-12 00:43:54 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676142311 Since half-lives follow exponential curves, does that mean that these half-lives extend infinitely? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676162019 Answer: The exponential curve continues indefinitely and is asymptotic as it approaches Y=0]]> 2021-08-12 01:02:01 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676162019 How does it go from -kt to kt in half life equations? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676164314 See image above]]> 2021-08-12 01:04:24 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676164314 Are recordings just on the week sections on canvas? I couldn't find them. I only found the slides. https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676164498 Answer: Refer to "Recorded lectures" linked to left hand menu on your unit canvas site.]]> 2021-08-12 01:04:35 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676164498 What is the difference between 1 1H and 1 1p? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676166244 Answer: See L2, slide 9. Both symbols be used represent Hydrogen nucleus. Worth noting is the 1H atom has an electron but 1p doesn't.]]> 2021-08-12 01:06:19 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676166244 Where does “ln” come from and what does it stand for in “equations for half life”? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676762384 ln comes from solving the exponential equation. ln is natural logarithm. ]]> 2021-08-12 12:49:10 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1676762384 How does half-life and radioactive decay relate? I'm having trouble interpreting this photo https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1678020090 See equation in lecture notes.
Activity (A) = rate constant (k) x Number of Nuclei (N)
K = ln 2 / Half life (t1/2)]]> 2021-08-13 10:28:55 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1678020090 Q2 on work sheet: Could you please re explain q2 i dont quite understand it yet. Thanks https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1678782123 The decay of an unstable nuclide is characterised by its half-life, which is the time required for half of the nuclei in a sample to undergo a decay event. The activity of a radioactive sample is a specific measure of the rate of decay, defined as the number of nuclei that disintegrate per second. If you see your notes, you'll find A=kN
Part (a) for example is asking "what period of time will the activity be for activity to be 50%", i.e., be 50/100 of A which means is A/2. Since A is proportional to N, you can simplify the question as what period of time will the number of nuclei, N become N/2 and you know this will take one half life. Hence, the answer is 20 minutes. For part b, the activity to be 25%, meaning N to become N/4 will require two half lives (40 mins), first to go from N to N/2 and then from N/2 to N/4 - each is reduction of a half.]]> 2021-08-14 02:33:06 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1678782123 Hello sir, would it be possible to get additional exercises/ practices with different question types? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679476322 Answer: If you've solved problems in the tutorial and homework worksheet, I'll suggest practice problems from the reference textbook - link can be found in the weekly pages.]]> 2021-08-15 14:37:55 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679476322 The example question for pre-lecture 1 quiz I don't understand how to answer it. Question: A sample contains 6.022 x 1022 molecules of the amine C4H9NH2. How many moles of C4H9NH2 does it contain? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679673489 See question answered above.]]> 2021-08-16 00:17:11 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679673489 Is there a relationship between stability and the rate of decay? E.g. the lower the stability the higher the rate of decay? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679673776 Not necessarily. Unstable nuclei can decay at varied half-life. Nuclei is either stable or not, i.e. either lies in zone of stability or not. You can't quantify the extent to which one nucleus is more stable than another. ]]> 2021-08-16 00:17:37 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679673776 For beta decay does it still have the same amount of electrons as the original atom? cfis54121 https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679681008 Yes. We have not discussed electrons yet. Note, radioactive decay is a nuclear reaction so pertains to nucleons.]]> 2021-08-16 00:28:18 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679681008 1. Do we need to be able to identify what type of decay an isotope will undergo? Or only identify what decay has been undergone?2. Will we be required to determine which isotopes are unable https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679682093 1. Depends on the question but Yes, you should be able to identify what kind of decay is likely if its established that nuclei is unstable. 2. Yes. You should be able to calculate N and Z and identify if the atom lies within the zone of stability. if yes, it is stable and if not, its not stable.]]> 2021-08-16 00:29:48 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679682093 This is a question from last week’s tutorial. When and how do we decide to use significant figures or precision numbers when answering questions? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679682773 Make it a habit to always consider significant figures while doing calculations. Just take care that significant figures of the resulting number is not more precise than the numerical inputs you used for your calculations.]]> 2021-08-16 00:30:48 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679682773 Hello! Can you upload a screenshot of the notes you wrote on your iPad during the lecture? Thanks! https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679689123 Please refer to lecture recording. Best to make notes while I am using whiteboard. Let me know if you are still struggling with this and if other students feel the same, I can make them available. ]]> 2021-08-16 00:39:34 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679689123 L4 Worksheet: For Q1, 3rd nuclear reaction, how do we know that it should be an alpha particle and not another isotope of helium (like the 2nd nuclear reaction which had atomic mass of 3)? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679693996 In the question we asked "identify the type of radioactive decay in each". He-3 isotope is not stable itself so not likely to be formed. Moreover, the six specific types of decay, including alpha decay, that we have studied are most commonly observed so most likely.]]> 2021-08-16 00:46:24 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679693996 Electron Capture: For EC Decay, is it only the atom's own electrons that can contribute to decay or can delocalised/free electrons such as in metals also induce EC? Thanks https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679710021 Not necessarily. Electron capture is generally defined as capture of electrons from the surrounding into the nucleus. ]]> 2021-08-16 01:06:23 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679710021 How do you know whether 11-C should increase neutrons or decrease protons? both of these options would make it lie in the zone of stability https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679711612 Correct. However, there are six types of radioactive decay that are most likely - these are ones we studied in Lecture 4. You got to identify which one among them is likely for 11-C.]]> 2021-08-16 01:08:15 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679711612 As C-14 has too many neutrons, would it be able to undergo neutron emission instead of beta decay to only lose a neutron? Is there a reason for it to undergo beta decay over neutron emission? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679713128 Well spotted. Neutron emission is also possible and likely.]]> 2021-08-16 01:10:01 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679713128 For the pre-lecture quiz 1, I didn't understand how to get the answer for question 2. A example of the question is question: How many molecules are there in 0.200 moles of C6H13NH2?could you please explain https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679794761 If I ask you how many oranges are in half a dozen, how will you find that out? I believe you'll approach it saying if a dozen means 12, half (0.5) dozen should be 0.5 x 12 = 6. So answer will 6 oranges.
Similarly, how many molecules are in 0.2 moles of C6H13NH2. One mole stands for quantity of 6.022 x 10 23. The number of molecules will be 0.2 x 6.022 x 10 23.]]> 2021-08-16 02:29:40 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1679794761 Positron (B+) decay: does a positron get released with B+ decay, with a 1 - P -0 just getting confused between when a positron is released and when a proton (1-P-1) is released https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1683019993 During Beta decay an electron is released from the nucleus while during a positron decay a positron is released from the nucleus. Don't confuse between a proton and a positron. We never talk about protons or neutrons leaving the nucleus. They can, however, interchange and when they do they release electron and positron in the process.

Both positron and electron are light sub-atomic particles with + and - charge, respectively. A proton is a positively charged particle that is much heavier than both of them.]]> 2021-08-18 00:06:16 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1683019993 Zone of Stability Curve: Does the curve shift away from N:Z = 1 as nucleons increase because of the strong nuclear attraction forces? Or another reason? Thanks https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1683059952 The curve shifts away from N/Z=1 when the number of protons increase. It has to do with how nuclear force (between nucleons) and proton-proton repulsion force counterbalance each other. You need to keep both factors in mind]]> 2021-08-18 00:35:27 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1683059952 Ionising Radiation https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1685737273 The Lecture slides state that "each unit" of radiation can ionise a large number of molecules. Does a unit here refer to only one of the particle E.g. One Alpha particle (He-4) ionises 500 000 molecules? ]]> 2021-08-19 08:23:47 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1685737273 How is the momentum of particle from its wavelength calculated? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1689498187 Momentum (p) is mass (m) of the particle multiplied by its velocity (v), i.e. p = mv. De Broglie's relationship link the momentum with wavelength, p = h / lambda, where h is the Plank's constant and lambda is the wavelength. 
PS. Padlet doesn't allow me to to use appropriate lowercase Greek symbol of wavelength so used text "lambda" instead. ]]> 2021-08-22 13:24:08 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1689498187 What is the Rydberg constant? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1689498575 It's a constant that essentially is a function of other constants i.e., mass of an electron, its charge and Plank's constant. In the nutshell, this constant replaced them in the Energy equation of Hydrogen atom simplifying the equation. ]]> 2021-08-22 13:24:59 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1689498575 Just want to confirm: more confinement = higher energies, correct? drmoffat https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1689867154 Yes]]> 2021-08-23 00:29:00 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1689867154 https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1689893412 how does squaring provide the measure of intensity or probability of finding electron’s location?]]> 2021-08-23 00:41:58 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1689893412 Do orbitals have an overall charge? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1689917509 Orbitals are representation of 3-dimensional surfaces that contains 90% of electron charge density. In a way, it represents a quantity, i.e., probability so avoid thinking that as a charge. ]]> 2021-08-23 00:53:49 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1689917509 In the 2D diagram of orbitals with the positive red region and blue negative region, do they only illustrate the position (above or below) of the wave or does it represent the wave function? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1689921595 The coloured regions are depiction of lobes within an orbital and the boundary that differentiates change in colour depicts a node, which can be circular or linear ]]> 2021-08-23 00:55:49 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1689921595 Are there any x-values we can input for the nodes? Are they constants? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1690007835 We haven't taught you how to calculate values of x where y=0 because its mathematically exhaustive for this unit. What I'd like you to be able to identify is number and type of nodes that will exist for a wavefunction and orbital.]]> 2021-08-23 01:34:29 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1690007835 for worksheet question 1, I understand everything up until y square is larger than 0 and A equals to 1. But I don't quite understand how we can draw the waves. how do we know the amplitude and the wavelength? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1693355771 Please go through pre-lecture video again to know how to characterise waves. Your tutorial worksheet will also discuss this in some depth.]]> 2021-08-24 09:57:49 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1693355771 Why does orbital size increase with energy? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1693465813 It doesn't necessarily increase with energy. Sorry my drawing wasn't good enough so gave you that impression. the sketch should fade out as we go far away from nucleus]]> 2021-08-24 12:09:31 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1693465813 How do we identify the principle quantum number https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1693466314 Principal quantum number is represented by n. For example, 1s orbital has a n=1, 2s and 2p orbitals has n=2... its the prefix attached to the orbital type s, p, d and f]]> 2021-08-24 12:09:57 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1693466314 Hello sir, would it be possible to have a 3D animation/youtube to see how the electron waves are around the nucleus? I understand the concept but can't really visualize it. https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1693545484 Visit www.falstad.com and check out Hydrogen atom applet ]]> 2021-08-24 13:04:20 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1693545484 What is a lobe? What is lobe represntation? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1694607984 Lobes represent 3-dimensional surfaces that contains 90% of electron charge density. ]]> 2021-08-25 00:08:29 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1694607984 How do orbitals have nodes? What part of the atom is this comparable to? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1694608872 Orbitals represent 3-dimensional surfaces that contains 90% of electron charge density]]> 2021-08-25 00:08:57 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1694608872 Radial Probability Curve: Is the area under the radial probability curve (for each orbital) equal always equal to 1? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1694618943 Overall probability of finding a particle can never be greater than 1, however, radial probability is representative 3-dimensional surface that contains 90% of electron charge density. ]]> 2021-08-25 00:14:08 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1694618943 Why does orbital size increase with energy https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1695241847 One of the learning outcomes of lecture 7 was " Explain why orbital size increases with energy" however I see that you answered that it doesn't necessarily do so under the previous lecture's padlet questions. I am slightly confused about this. Thanks!

]]> 2021-08-25 04:09:13 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1695241847 Why the principal quantum number can’t differentiate between 2p and 2s. rzha54471 https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1695947342 Principal number for both 2s and 2p is the same, i.e. 2]]> 2021-08-25 12:51:50 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1695947342 Planar and spherical nodes https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1697042797 How can you determine whether an orbital has a spherical or planar node? Is there a way to differentiate how many planar/spherical nodes make up the quantum number n? ]]> 2021-08-26 00:13:33 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1697042797 What are hydrogen like atoms? What does this include? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1697120169 2021-08-26 00:43:38 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1697120169 Is the principle quantum number (n) the same as the electron shell? So the first shell is when n = 1, second shell is when n = 2, etc.? I understand we haven't talked about shells, but just trying to visualise. https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1697407132 Shell is a classical concept. For multi-electron systems we  invoked the quantum theory, where n helps define energy and size of the orbital.]]> 2021-08-26 02:24:32 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1697407132 Does planer=linear nodes as well as circular=spherical nodes? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1698526795 Is the difference it's just 2D and 3D representation so it will be fine if I say either to describe the orbital ?! ]]> 2021-08-26 14:07:03 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1698526795 I am sorry, but can you have more clear handwriting, since I wouldn’t drop down almost all of your handwritten notes on worksheets/whiteboard, which makes me super confused about the topics. Thank you very much https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1701938009 Sure, I'll work on it.]]> 2021-08-28 13:05:45 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1701938009 valence electrons: Why do you count the electrons in the 3d shells as well as the 4s shell for valence for titanium??? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1703109221 When we think of valence electrons, the best way to determine them is count the number of electrons outside the rare-gas (or Nobel gas or inert gas or shorthand) configuration. In the case of Ti the rare gas configuration can be written as [Ar] 4s2 3d2, hence, total number of valence electrons are 2 + 2 = 4. The caveat here is that once 3d orbitals are full, they become non-reactive so not count them in valence electrons, for e.g. lets consider Br which has rare gas configuration of [Ar] 4s2 3d10 4p5, here, we won't count filled d orbital so total number of valence electrons will be 2 + 5 = 7]]> 2021-08-30 00:36:39 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1703109221 Regarding question 2 on the lecture 9 worksheet: I understand why question 2a = 3 electrons; however, I do not understand why question 2b = 7 electrons. When I added up 1s^2 2s^2 2p^5, I calculated it as 9 total electrons. Looking at the periodic table, the Z value of where we placed it on the periodic table is also 9 (Fluorine). I am just curious where you got the 7 from? Is it because it is in the 7th row? Thank you! drmoffat https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1703139026 The 7 came from the row number or number or valence electrons assuming d orbitals are full.]]> 2021-08-30 00:49:42 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1703139026 About pre LEC quiz, one of the questions was about titanium and it says that Ti lies on “d”, but should it not be lying on “p” https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1704363475 3d orbitals fill up after 4s but before 4p - see lecture 9 notes to recall on the order in which orbitals fill up.
Shorthand configuration of Ti is [Ar] 4s2 3d2]]> 2021-08-30 12:21:16 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1704363475 This is a follow-up to my previous question regarding #2 on the worksheet. I now understand that the 7 came from the row number. Why was the answer 3 electrons for question 2a if it was in the first row? These questions may be hard to describe over message so if you prefer I ask during class I can follow up then! drmoffat https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1705323137 2a is 1s2 2s1 so has total 2+ 1 = 3 electrons - 2 electrons in 1s and one electron in 2s. When you fill up a periodic table you go left to right and then top to bottom in incremental order.]]> 2021-08-30 20:26:58 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1705323137 why would an atom's ionisation energy not fit the trend of what we've learnt? (question 5f on lecture worksheet) https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1707091391 We did this question first thing in L11. Refer to recordings. If. it still isn't clear, share your working/approach so I can best address it.]]> 2021-08-31 13:30:27 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1707091391 Orbitals, energy levels concept mix up I’m starting to get really confused with how many electrons each energy level/ orbital can occupy/have. For example, for S, is it 2 (because each orbital can only occupy 2 electrons) OR is it 4 (because it is 3p^4) OR is it 6 (because it is 2 electrons away from inert Ar) https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1710409993 From your question above, it's not clear to me what aspect of this is confusing to you. I'd suggest go through lectures because it appears to me you're focussing more on solving problems rather than revisiting the concepts that are confusing you. Here is how to approach it,

Orbitals are electron density that emerge from electron wave functions. Each electron wave function and in turn orbital, has energy associated to it (same way as different waves on a guitar string have different energy associated to it). 

- We studied s, p, d and f orbitals. 

- We also studied that there can be one kind of s orbital, 3 kinds of p orbitals (px, py, pz) and five kinds of f orbitals. 

- We studied each orbital can hold 2 electrons  max with different spins. This means any s orbital can hold max 2 electrons, p orbitals can hold max 6 electrons (2 each in px, py and pz) and similarly d orbitals can hold max 10 electrons. 

- Now when you want to identify an electronic configuration, we studied that this is best done by first identifying the atomic number of atom, then calculating number of electrons (which will depend if its neutral or ionic) and then fill atomic orbitals in order of their increasing energy following four rules we defined in the lecture. ]]> 2021-09-01 16:52:00 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1710409993 BONDING AND ANTIBONDING ORBITAL - How do we know if the atom or molecule has higher energy? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1711115852 Antibonding orbitals have one extra planar node compared bonding orbitals, hence, are higher in energy]]> 2021-09-02 00:19:05 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1711115852 How do you know where the electrons go in the molecule? Why do the go to sigma and sigma* first instead of 1s? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1711132276 1s is an atomic orbital. Sigma and sigma* are molecular orbitals. When you're finding electronic configuration of an atom, you will atomic orbitals and when you're writing configuration for a molecule, you use molecular orbitals.]]> 2021-09-02 00:25:54 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1711132276 I wonder why positions of sigma and pi can exchange in C2 and F2? And how can I justify who has higher energy? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1711298202 Its because of s-p mixing. We haven't discussed this concept in the lecture and its not part of this unit. However, I have tried to discuss this in one of the questions above.]]> 2021-09-02 01:21:55 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1711298202 As there are many orbital shapes possible, how do we identify which shape is for which orbital? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1711576281 What I'd like you to be able to do is identify/recognise sigma and pi MOs originating from combination of different sets of atomic orbitals such as 1s, 2s and 2p. Recall, anti bonding MOs will always have one more planar node than bonding MOs. Also worth knowing is how p orbitals can give rise to both sigma and pi MOs depending on if interaction is end-on or side-on.]]> 2021-09-02 02:56:47 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1711576281 Do only valence electrons contribute to the molecular orbital overlap? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1714404285 Only valence electrons determine chemical bonding. See Lec 11 for examples.]]> 2021-09-03 03:06:43 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1714404285 in heteronuclear molecules, how do you know which orbitals line up between the two molecules? e.g how in HF the 1s of H lines up with 2p of F https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1714439559 The take home message while thinking about which orbitals line up in heteronuclear diatomic molecule is to consider which one of the atoms have lower energy. One with lower energy will have atomic orbitals pulled down compared to other one. This is easier when both atoms are in the same period, for e.g. recall bond between H and He we studied in the lecture. He has larger Zeff so lower in energy than H. While considering molecules like HF this is trickier. That said, the 1s orbital in F is core electron so not reactive, hence much, lower in energy compared to 1s1 in H (which while is closer to H nucleus but in valence shell) so 2p of F lines up with 1s of H instead.

Please note, MO diagram will be provided to you so I don't expect you to know how these MO originate in heteronuclear diatomic molecules. ]]> 2021-09-03 03:21:41 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1714439559 In the example HF, we start plotting electrons from 2s orbital. How do we know where to start plotting the electrons for other molecules or whether an orbital is non-bonding.... but then in pre lec quiz for week 5, although it says "1s is not included", I still have to plot electrons starting from 1s https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1714815030 While considering filling electrons in MO diagram, there is one key point to pay particular attention to, i.e., whether the MO diagram provided shows the energies of the orbitals for the valence electrons or all the electrons. For the former, you only need to be concerted with total number of valence electrons in the molecule, however, for latter you need to calculate all the electrons in the molecule (both core and valence). Hope this helps.

]]> 2021-09-03 07:21:17 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1714815030 I understand that in the end, bond order is the same. But I would like to ask why the sequence is different/ how we can determine if we can switch up the sequence (for top pic: sigma, pi, pi*, sigma* / for bottom pic: pi, sigma, pi*, sigma*) https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1716543806 The order depends on the mixing of different atomic orbitals and comparative energy offset while forming bonding molecular orbitals. For e.g., let's consider C2 bond formation where each C atom has 4 electrons in atomic orbitals 2s2 and 2p2. Now when two C atoms come closer, two 2s orbitals will combine to form two MO orbitals - sigma and sigma*, while two sets of p orbitals (mind you three of them in each namely px, py and pz) will combine to form one sigma and two pi bonding and one sigma* and two pi* anti bonding MOs. Now given 2s and 2p orbitals are fairly separated in C, sigma and pi are MO are fairly well separated with pi orbitals higher in energy than sigma, however, when we move across a period from C to N to O to F, 2s and 2p orbitals are fairly close plus the act of p orbitals already paired up also increases its energy relative to unpaired 2p orbitals causing mixing of orbitals in such a way that Pi can now be lower in energy than sigma orbitals. This is often referred to as s-p mixing. We haven't discussed this in lectures so I don't expect you to know this. Moreover, we will always provide you with MO diagram so don't expect you to be able to construct them so don't get worried if you can't find the arrangements. Have a look at learning outcomes at the end of the lecture to know what is expected from you to know after the end of the lecture. Hope this helps.]]> 2021-09-04 11:42:28 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1716543806 Are we supposed to know all the shapes of pi and sigma bonds https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1717919368 At the end of every lecture, we have stated learning outcomes of that lecture. Those clearly outline what we expect you to know for that lecture. Have a look at that.]]> 2021-09-06 00:29:31 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1717919368 how do we know among the px, py, pz of the 2p orbital, which 2 are the non bonding orbitals? or is it the same every time https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1719402836 As you can imagine, px, py and pz orbitals gain their relevance form orientation, i.e. pointing in x, y and z directions. Now x/y/z axis you draw on your sheet of paper maybe different from what I draw here. In the nutshell, it is hard for me to say which of px py and pz will be non-bonding because we may not share the same frame of reference.

What we can say with certainty is that in the example (HF) where we alluded to non-bonding orbitals, is that HF form sigma bonding and anti bonding molecular orbitals (MO) first, as is always the case when p orbitals combine, first sigma MOs are formed and then pi MOs. Given H has only 1s orbital partaking in bond formation (with 3 x 2p from F), it is consumed by one of the p orbitals to form sigma and sigma* MOs and the leftover 2 x 2p orbitals of F become non-bonding.

Contrarily, if you were forming an F2 molecule, 3 x 2p orbitals from both F are available to form MOs so sigma and sigma* and two degenerate sets of pi and pi* MOs will be formed.

Hope this helps. If not, feel free to put in a follow up question]]> 2021-09-06 13:51:12 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1719402836 hello sivir https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1734368027 2021-09-13 00:15:52 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1734368027 Formal charge: Is there a way to determine the overall formal charge of a resonance structure? https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1734487438 Formal charges are calculated for each atom within a molecule. You can't average formal charge for same atom in different resonance structures, if that is what you're referring to. ]]> 2021-09-13 01:09:12 UTC https://padlet.com/girishlakhwani1/n7p2zqzmypxwil0w/wish/1734487438