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Formal charge: Is there a way to determine the overall formal charge of a resonance structure? 

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Formal charge: Is there a way to determine the overall formal charge of a resonance structure? 

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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.

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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

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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

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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

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Are we supposed to know all the shapes of pi and sigma bonds

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Are we supposed to know all the shapes of pi and sigma bonds

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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.

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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*)

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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*)

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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.

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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

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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

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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.

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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

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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

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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.

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Do only valence electrons contribute to the molecular orbital overlap?

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Do only valence electrons contribute to the molecular orbital overlap?

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Only valence electrons determine chemical bonding. See Lec 11 for examples.

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As there are many orbital shapes possible, how do we identify which shape is for which orbital?

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As there are many orbital shapes possible, how do we identify which shape is for which orbital?

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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.

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I wonder why positions of sigma and pi can exchange in C2 and F2? And how can I justify who has higher energy?

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I wonder why positions of sigma and pi can exchange in C2 and F2? And how can I justify who has higher energy?

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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.

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How do you know where the electrons go in the molecule? Why do the go to sigma and sigma* first instead of 1s?

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How do you know where the electrons go in the molecule? Why do the go to sigma and sigma* first instead of 1s?

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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.

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BONDING AND ANTIBONDING ORBITAL - How do we know if the atom or molecule has higher energy?

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BONDING AND ANTIBONDING ORBITAL - How do we know if the atom or molecule has higher energy?

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Antibonding orbitals have one extra planar node compared bonding orbitals, hence, are higher in energy

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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)

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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)

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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.

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why would an atom's ionisation energy not fit the trend of what we've learnt? (question 5f on lecture worksheet)

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why would an atom's ionisation energy not fit the trend of what we've learnt? (question 5f on lecture worksheet)

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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.

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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!

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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!

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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.

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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”

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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”

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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

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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!

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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!

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The 7 came from the row number or number or valence electrons assuming d orbitals are full.

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valence electrons: Why do you count the electrons in the 3d shells as well as the 4s shell for valence for titanium???

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valence electrons: Why do you count the electrons in the 3d shells as well as the 4s shell for valence for titanium???

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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

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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

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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

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Sure, I'll work on it.

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Does planer=linear nodes  as well as circular=spherical nodes? 

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Does planer=linear nodes  as well as circular=spherical nodes? 

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Is the difference it's just 2D and 3D representation so it will be fine if I say either to describe the orbital ?!

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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.

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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.

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Shell is a classical concept. For multi-electron systems we  invoked the quantum theory, where n helps define energy and size of the orbital.

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What are hydrogen like atoms? What does this include?

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What are hydrogen like atoms? What does this include?

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Why the principal quantum number can’t differentiate between 2p and 2s. 

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Why the principal quantum number can’t differentiate between 2p and 2s. 

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Principal number for both 2s and 2p is the same, i.e. 2

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Why does orbital size increase with energy

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Why does orbital size increase with energy

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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!

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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?

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Radial Probability Curve: Is the area under the radial probability curve (for each orbital) equal always equal to 1? 

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Radial Probability Curve: Is the area under the radial probability curve (for each orbital) equal always equal to 1? 

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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.

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What is a lobe? What is lobe represntation?

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What is a lobe? What is lobe represntation?

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Lobes represent 3-dimensional surfaces that contains 90% of electron charge density.

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How do orbitals have nodes? What part of the atom is this comparable to?

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How do orbitals have nodes? What part of the atom is this comparable to?

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Orbitals represent 3-dimensional surfaces that contains 90% of electron charge density

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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.

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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.

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Visit www.falstad.com and check out Hydrogen atom applet

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How do we identify the principle quantum number

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How do we identify the principle quantum number

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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

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Why does orbital size increase with energy?

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Why does orbital size increase with energy?

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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

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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?

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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?

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Please go through pre-lecture video again to know how to characterise waves. Your tutorial worksheet will also discuss this in some depth.

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Are there any x-values we can input for the nodes? Are they constants?

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Are there any x-values we can input for the nodes? Are they constants?

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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.

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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?

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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?

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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

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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.

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how does squaring provide the measure of intensity or probability of finding electron’s location?

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Just want to confirm: more confinement = higher energies, correct?

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Just want to confirm: more confinement = higher energies, correct?

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Yes

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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.

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How is the momentum of particle from its wavelength calculated?

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How is the momentum of particle from its wavelength calculated?

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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.

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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?

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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

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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

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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

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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

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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

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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.

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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

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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

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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.

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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?

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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?

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Well spotted. Neutron emission is also possible and likely.

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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

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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

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Not necessarily. Electron capture is generally defined as capture of electrons from the surrounding into the nucleus.

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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)?

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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)?

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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.

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Hello! Can you upload a screenshot of the notes you wrote on your iPad during the lecture? Thanks!

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Hello! Can you upload a screenshot of the notes you wrote on your iPad during the lecture? Thanks!

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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.

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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? 

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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? 

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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.

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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

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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

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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.

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For beta decay does it still have the same amount of electrons as the original atom? 

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For beta decay does it still have the same amount of electrons as the original atom? 

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Yes. We have not discussed electrons yet. Note, radioactive decay is a nuclear reaction so pertains to nucleons.

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Is there a relationship between stability and the rate of decay? E.g. the lower the stability the higher the rate of decay? 

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Is there a relationship between stability and the rate of decay? E.g. the lower the stability the higher the rate of decay? 

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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.

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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?

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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?

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See question answered above.

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Hello sir, would it be possible to get additional exercises/ practices with different question types?

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Hello sir, would it be possible to get additional exercises/ practices with different question types?

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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.

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Q2 on work sheet: Could you please re explain q2 i dont quite understand it yet. Thanks 

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Q2 on work sheet: Could you please re explain q2 i dont quite understand it yet. Thanks 

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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.

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How does half-life and radioactive decay relate? I'm having trouble interpreting this photo 

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How does half-life and radioactive decay relate? I'm having trouble interpreting this photo 

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See equation in lecture notes.
Activity (A) = rate constant (k) x Number of Nuclei (N)
K = ln 2 / Half life (t1/2)

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Where does “ln” come from and what does it stand for in “equations for half life”?

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Where does “ln” come from and what does it stand for in “equations for half life”?

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ln comes from solving the exponential equation. ln is natural logarithm.

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What is the difference between 1 1H and 1 1p?

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What is the difference between 1 1H and 1 1p?

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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.

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Are recordings just on the week sections on canvas? I couldn't find them. I only found the slides.

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Are recordings just on the week sections on canvas? I couldn't find them. I only found the slides.

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Answer: Refer to "Recorded lectures" linked to left hand menu on your unit canvas site.

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How does it go from -kt to kt in half life equations?

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How does it go from -kt to kt in half life equations?

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See image above

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Since half-lives follow exponential curves, does that mean that these half-lives extend infinitely?

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Since half-lives follow exponential curves, does that mean that these half-lives extend infinitely?

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Answer: The exponential curve continues indefinitely and is asymptotic as it approaches Y=0

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Is there an official way of writing 2,3,4 etc half lives? 

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Is there an official way of writing 2,3,4 etc half lives? 

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Answer: Half life is written as t1/2. You can write the rest as 2 t1/2, 3 t1/2, 4 t1/2

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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? 

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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? 

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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.

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The cancellation of the equation is not clear. Could you please explain it again？

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The cancellation of the equation is not clear. Could you please explain it again？

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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.

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Why is lithium skipped in the helium to the red giant section? 

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Why is lithium skipped in the helium to the red giant section? 

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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.

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Do we need to memorise the life cycle of stars?

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Do we need to memorise the life cycle of stars?

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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.

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Is the protons not equal on both sides in the overall hydrogen burning reaction?

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Is the protons not equal on both sides in the overall hydrogen burning reaction?

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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.

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What is the purpose of simplifying all 3 reactions?

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Should we memorise the 3 hydrogen burning equations?

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Should we memorise the 3 hydrogen burning equations?

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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.

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Difference between proton and positron except for their mass difference

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Difference between proton and positron except for their mass difference

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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.

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Will the final exam be open book or closed book?

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Will the final exam be open book or closed book?

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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.

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Answer: Its spelled as Stoichiometry. Its the calculation of reactants and products in the chemical reaction

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Nuclear transformation: So can any element be transformed into any other element as long as it's balanced?

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Nuclear transformation: So can any element be transformed into any other element as long as it's balanced?

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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.

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Answer: its a subatomic particle with +1 charge

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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? 

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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? 

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Answer: Not necessarily. It would depend on what other products are formed in the reaction. Remember, equations need to be balanced.

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Periodic table: Could you explain how to read Periodic table again?

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Periodic table: Could you explain how to read Periodic table again?

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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.

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Answer: You will find them in radioactive decay reactions.

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overall hydrogen burning reaction: why are the 2 protons crossed out?

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overall hydrogen burning reaction: why are the 2 protons crossed out?

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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

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Are there Pre-lecture videos we need to watch and if so where are they? 

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Are there Pre-lecture videos we need to watch and if so where are they? 

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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.

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Ans: brilliant

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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

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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

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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.