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    Made a thread for all of us doing AH chemistry to discuss the course, prelims, ask questions and the investigation.

    What stage is everyone at with the course and investigation?
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    Probably the most boring and difficult course i have ever encountered, horrendous
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    Hello chemists!
    Hows every much everyone finding AH? Have you had your prelim yet?

    I'm really struggling with unit 2, I just don't seem to be understanding any of the content. What resources have you been using for revision?

    Can anyone explain what exactly molecular orbitals are and how they form and how bonding in Alkanes and alkenes work with pi and sigma bonds?
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    (Original post by Ethan100)
    Hello chemists!
    Hows every much everyone finding AH? Have you had your prelim yet?

    I'm really struggling with unit 2, I just don't seem to be understanding any of the content. What resources have you been using for revision?

    Can anyone explain what exactly molecular orbitals are and how they form and how bonding in Alkanes and alkenes work with pi and sigma bonds?
    Hia! My prelim is in a week (not looking forward to it!) Yeah Unit 2 is defo the hardest- there's so much to remember!
    I've haven't done as much revision as I should have for it, but the SQA course and unit support notes are always useful (see https://www.sqa.org.uk/files_ccc/AHCUSNChemistry.pdf ) and Scholar is amazing- I don't know if your school has it but it's really good.

    Ok, so, to answer your questions:

    Molecular orbitals:
    When atoms approach each other, their separate sets of atomic orbitals merge to form a single set of molecular orbitals. Some of the molecular orbitals, known as 'bonding molecular orbitals', occupy the region between two nuclei. The attraction of positive nuclei to negative electrons occupying bonding molecular orbitals is the basis of bonding between atoms. Each molecular orbital can accommodate a maximum of two electrons. Molecular orbitals are usually constructed by combining atomic orbitals or hybrid orbitals from each atom of the molecule.

    Pi bonds and sigma bonds:
    A covalent bond is formed when two half-filled atomic orbitals overlap. If they overlap along the axis of the bond (end on) a covalent bond is known as a sigma (σ) bond. Pi (π) bonds arise where atoms make multiple bonds, for example the double bond in a molecule of oxygen O2 is made up of one sigma and one pi bond. The triple bond in a molecule of nitrogen N2 is made up of one sigma and two pi bonds. Pi bonds are formed when atomic orbitals lie perpendicular to the bond and overlap side on. End to end overlap is more efficient than side on overlap and therefore σ bonds are stronger than π bonds.

    Sigma and pi bonds specifically in hydrocarbons:
    Let's look at an alkane, ethane for example. Each carbon has three 2p orbitals and one 2s orbital which mix to form four degenerate (equal energy) hybrid orbitals. These are known as sp3 hybrid orbitals and point towards the corners of a tetrahedron in order to minimise repulsion from each other. The four sp3 orbitals on each carbon atom overlap end to end with one sp3 orbital on the other carbon atom and the three hydrogen 1s orbitals. This forms 4 σ bonds. The bonding in ethane can be described as sp3 hybridisation and sigma bonds.

    If we take a look at the bonding in the corresponding alkene ethene we can see that the 2s orbital and two of the three 2p orbitals mix on each carbon atom to form three sp2 hybrid orbitals. To minimise repulsion these orbitals form a trigonal planar arrangement. The carbon atoms use the three sp2 hybrid orbitals to form sigma bonds with two hydrogen atoms and with the other carbon atom. The unhybridised 2p orbitals left on the carbon can overlap side-on to form a pi bond.


    Hope this helps!
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    (Original post by Keen Bean #1)
    Hia! My prelim is in a week (not looking forward to it!) Yeah Unit 2 is defo the hardest- there's so much to remember!
    I've haven't done as much revision as I should have for it, but the SQA course and unit support notes are always useful (see https://www.sqa.org.uk/files_ccc/AHCUSNChemistry.pdf ) and Scholar is amazing- I don't know if your school has it but it's really good.

    Ok, so, to answer your questions:

    Molecular orbitals:
    When atoms approach each other, their separate sets of atomic orbitals merge to form a single set of molecular orbitals. Some of the molecular orbitals, known as 'bonding molecular orbitals', occupy the region between two nuclei. The attraction of positive nuclei to negative electrons occupying bonding molecular orbitals is the basis of bonding between atoms. Each molecular orbital can accommodate a maximum of two electrons. Molecular orbitals are usually constructed by combining atomic orbitals or hybrid orbitals from each atom of the molecule.

    Pi bonds and sigma bonds:
    A covalent bond is formed when two half-filled atomic orbitals overlap. If they overlap along the axis of the bond (end on) a covalent bond is known as a sigma (σ) bond. Pi (π) bonds arise where atoms make multiple bonds, for example the double bond in a molecule of oxygen O2 is made up of one sigma and one pi bond. The triple bond in a molecule of nitrogen N2 is made up of one sigma and two pi bonds. Pi bonds are formed when atomic orbitals lie perpendicular to the bond and overlap side on. End to end overlap is more efficient than side on overlap and therefore σ bonds are stronger than π bonds.

    Sigma and pi bonds specifically in hydrocarbons:
    Let's look at an alkane, ethane for example. Each carbon has three 2p orbitals and one 2s orbital which mix to form four degenerate (equal energy) hybrid orbitals. These are known as sp3 hybrid orbitals and point towards the corners of a tetrahedron in order to minimise repulsion from each other. The four sp3 orbitals on each carbon atom overlap end to end with one sp3 orbital on the other carbon atom and the three hydrogen 1s orbitals. This forms 4 σ bonds. The bonding in ethane can be described as sp3 hybridisation and sigma bonds.

    If we take a look at the bonding in the corresponding alkene ethene we can see that the 2s orbital and two of the three 2p orbitals mix on each carbon atom to form three sp2 hybrid orbitals. To minimise repulsion these orbitals form a trigonal planar arrangement. The carbon atoms use the three sp2 hybrid orbitals to form sigma bonds with two hydrogen atoms and with the other carbon atom. The unhybridised 2p orbitals left on the carbon can overlap side-on to form a pi bond.


    Hope this helps!
    Wow thank you so much!!!!

    Good Luck with your prelim! Let us know how it goes
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    (Original post by Ethan100)
    Wow thank you so much!!!!

    Good Luck with your prelim! Let us know how it goes
    Thank you, will do! That's fine, happy to help out
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    (Original post by Ethan100)
    Hello chemists!
    Hows every much everyone finding AH? Have you had your prelim yet?

    I'm really struggling with unit 2, I just don't seem to be understanding any of the content. What resources have you been using for revision?

    Can anyone explain what exactly molecular orbitals are and how they form and how bonding in Alkanes and alkenes work with pi and sigma bonds?
    I only get 2 periods a week so only recently began unit 2 so can't really say much about it haha. unit 1 is alright just practicing questions. My prelim is at the start of Feb but I'm not really bothered about it av lost the will.
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    (Original post by Ethan100)
    Hello chemists!
    Hows every much everyone finding AH? Have you had your prelim yet?

    I'm really struggling with unit 2, I just don't seem to be understanding any of the content. What resources have you been using for revision?

    Can anyone explain what exactly molecular orbitals are and how they form and how bonding in Alkanes and alkenes work with pi and sigma bonds?
    Aww god you're worrying me by saying that about Unit 2! I just did my Unit 1 NAB last week and thankfully passed it, but I felt like I really struggled with a lot of the unit... I was hoping Unit 2 would be a wee bit easier More hard work for me I guess.

    My prelim is on 25th Jan, can't say I'm looking forward to it but studying hard. I can't comment on U2 but Scholar and the BrightRed textbook have been my most useful resources. Hope everyone is doing well with the course and also UCAS stuff and the like. Best of luck for upcoming prelims! :yikes:
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    (Original post by thatscottishkid)
    Aww god you're worrying me by saying that about Unit 2! I just did my Unit 1 NAB last week and thankfully passed it, but I felt like I really struggled with a lot of the unit... I was hoping Unit 2 would be a wee bit easier More hard work for me I guess.

    My prelim is on 25th Jan, can't say I'm looking forward to it but studying hard. I can't comment on U2 but Scholar and the BrightRed textbook have been my most useful resources. Hope everyone is doing well with the course and also UCAS stuff and the like. Best of luck for upcoming prelims! :yikes:
    Sorry! You should find it fine, just quite a lot of experiments, reactions, catalysts to remember.

    I am having my unit 1 NAB next week so hope that goes well for me, not feeling too confident I must say


    Anyone that has done Unit 2,
    What questions would likely come up on Sn1 and Sn2 reactions? Just a description of each mechanisms or actually showing each step using curly arrow notation.
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    (Original post by Ethan100)
    Sorry! You should find it fine, just quite a lot of experiments, reactions, catalysts to remember.

    I am having my unit 1 NAB next week so hope that goes well for me, not feeling too confident I must say


    Anyone that has done Unit 2,
    What questions would likely come up on Sn1 and Sn2 reactions? Just a description of each mechanisms or actually showing each step using curly arrow notation.
    the unit 1 nab is easy don't worry! Some questions were worded **** though haha
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    My prelim is on Tuesday and we’ve been through all of Unit 1 and 2, but there’s so much to remember and buffers and indicators are so hard to wrap your head around...

    HIn (aq) + H2O (l) <-> H3O+ (aq) + In- (aq)

    I don’t get how adding an acid to the indicator dissociation equilibrium shifts the equilibrium to the left? I thought an acid would react with the negative indicator ion on the right of the equation, wouldn’t that shift the equilibrium to the right? I might be completely wrong so if someone could help
    me that would be great.
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    thought I’d jump on this thread since my prelim is on tuesday
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    chemical equilibrium is a *****
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    Can someone explain Kinetics and reaction feasibility?!?
    So difficult
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    thanks
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    What stage is everyone at with the project? Trying to find a method right now and totally confused
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    (Original post by erinkelly22x)
    What stage is everyone at with the project? Trying to find a method right now and totally confused
    We haven't started our actual experiments, but we've done the underlying chemistry, method, risk assessment and technician request (equipment/chemicals).
    What is your project on?
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    (Original post by Keen Bean #1)
    We haven't started our actual experiments, but we've done the underlying chemistry, method, risk assessment and technician request (equipment/chemicals).
    What is your project on?
    My project topic is investigating the Vitamin C content in fruit juices, but I’ve changed my aim quite a few times because I didn’t understand it 😂 We have to do our practical this week but everything else is to be done in our spare time, what’s yours on?
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    I'm doing synthesis of sulphanilamide and I've done most of the practical work but still need to figure out how to test it as an antibacterial. I've done most of my method and the risk assessment but I haven't started underlying chemistry yet and I have absolutely no idea where to start
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    (Original post by katiegray)
    I'm doing synthesis of sulphanilamide and I've done most of the practical work but still need to figure out how to test it as an antibacterial. I've done most of my method and the risk assessment but I haven't started underlying chemistry yet and I have absolutely no idea where to start
    That’s what I’m doing as well! I hated the practical haha using chlorosulfonic acid was awful. Like you I’ve finished all the practical and I might test the antibacterial properties but it seems quite complicated so it depends on whether I have time. How successful were your synthesises? Mine produced three visually completely different compounds but were still relatively pure but didn’t have very high percentage yields.

    My teacher gave me a past project write up to take ideas from and in the underlying chemistry they talk about the history and function of sulphanilamide and a brief explanation of what they did during the synthesis in relation to the structure. Also talk about techniques you’ve used, such as melting point analysis and TLC. If you use the bacteria you can put that in there as well and if you’ve obtained spectroscopy results. I’m struggling with that area as well because I only have IR spectrums for 2/3 synthesises and haven’t done the bacteria (yet), so haven’t got a lot to talk about.
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