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# AS Chemistry- helping each other out! watch

1. You know how we say that to calculate the number of electrons a shell can hold, we use the formula 2n2??? e.g the 3rd shell has a maximum capacity of 18 electrons according to the equation, so why do we draw shells in sets of 8 electrons? (apart from the 1st shell)
2. (Original post by Georgiam247)
You know how we say that to calculate the number of electrons a shell can hold, we use the formula 2n2??? e.g the 3rd shell has a maximum capacity of 18 electrons according to the equation, so why do we draw shells in sets of 8 electrons? (apart from the 1st shell)
you don't, you follow the sub level idea behind the shells, so for example say you're looking at sodium which has 11 electrons, you'd say that its electronic configuration would be 1S2 2S2 2P6 3S1 so the first shell has 2 electrons, the second has 8 and the third one. You can have shells that are occupied by even 18 electrons.. i.e caesium
you don't, you follow the sub level idea behind the shells, so for example say you're looking at sodium which has 11 electrons, you'd say that its electronic configuration would be 1S2 2S2 2P6 3S1 so the first shell has 2 electrons, the second has 8 and the third one. You can have shells that are occupied by even 18 electrons.. i.e caesium
So really the octet rule is inaccurate and not advanced enough? Thank you
4. hi
i just wanted to know if anyone has got or knows where to find the june 2014 chemistry aqa unit 1 and 2 question papers???
5. (Original post by HToo)
hi
i just wanted to know if anyone has got or knows where to find the june 2014 chemistry aqa unit 1 and 2 question papers???
Sharing last years papers is prohibited, as is asking for them.
6. Can someone explain something to me. It is to do with bond angles.

4a). PH4+ . The plus represents it has lost an electron. Now is the electron being lost from the phosphorous or the hydrogen.

another one 4c) PF6- . So one phosphorous and 6 flourines. Has the phosphorous gained an electron or the chlorine. Slight confused on how it works.

Thanks
7. (Original post by Super199)
Can someone explain something to me. It is to do with bond angles.

4a). PH4+ . The plus represents it has lost an electron. Now is the electron being lost from the phosphorous or the hydrogen.

another one 4c) PF6- . So one phosphorous and 6 flourines. Has the phosphorous gained an electron or the chlorine. Slight confused on how it works.

Thanks
a) think of an ammonium ion? It is dative covalent bonding a PH3 molecule is trigonal pyramidal in shape. Bond angle of 107' When a proton comes along, the PH3 will donate it's lone pair of electrons to the proton and dative covalently bonds therefore the new bond angle is 109.5, ygm?

c) The bond angle will be 90', octahedral shape
8. (Original post by frozo123)
a) think of an ammonium ion? It is dative covalent bonding a PH3 molecule is trigonal pyramidal in shape. Bond angle of 107' When a proton comes along, the PH3 will donate it's lone pair of electrons to the proton and dative covalently bonds therefore the new bond angle is 109.5, ygm?

c) The bond angle will be 90', octahedral shape
Yeah got it sound g
9. Anyone up for skype revision or email revision? D: on OCR A
10. (Original post by Singh_0115)
Anyone doing ocr A wanna help each other with course works practicals message me I've done a 2 of each so far but I'm aiming for 80% so need some help!

Posted from TSR Mobile
Please look 1 post above your's.
Many Thanks.
11. I'm having trouble finding the enthalpy change of combustion of hydrogen in my data book, I'm on Edexcel, can anyone help?
12. For Edexcel AS Chemistry are there certain practicals we need to know for the exams? I've seen the crystals one come up a few times in the past papers I've done, are there any more?
13. (Original post by jerseyalevel)
For the 'Green Chemistry' topic of the Unit 2 Exam in AS OCR A, how much detail do we need to go into? Im a little lost as to whether we need to know lots of examples etc.

Thanks
The question which seems to crop up a lot over the past years has been how catalytic converters work - Absorption of CO and NO which weakens the bonds (held onto the metal surface), by the metal surface of the converter. Bonds form with the metal surface, these hold the gas molecules in the correct position for a reaction to occur. These are then Desorbed by the surface, releasing C02 and N2.

(Original post by Super199)
Can someone explain the displacement reactions for the halogens. Is the reason why bromine cannot displace chlorine due to chlorine being more reactive than it. Also when bromine displaces say potassium iodide do you get an orange or brown solution?
A more reactive halogen displaces a weaker halogen, that's the essential theory - this is known as a Displacement reaction as you've said. And so, Chlorine can displace both Br2 and I2, Br2 can only displace I2, whereas I2 can't displace anything as said halogens are more reactive.
Br2 + 2I- -> 2Br- + I2
To detect the presence of Iodine, in water it would be brown and in cyclohexane it would be violet.
14. (Original post by tobeobi)
Can someone please give me a step by step guideline on how to predict the shapes and bond angles in molecules and ions? I find this really difficult and the book only confuses me
Okay, a bit of exam technique; Always mention the number of bonded and lone pairs.
Always mention that if a molecule only has bonded pairs the electron pair repulsion is equally and this causes the molecule to spread out as far as possible.
And always mention, lone pairs repel more than electron pairs.

This is the tedious bit, this is just a case of remembering all the different shapes and bond angles. They'll give you a molecule, it may help to draw a Dot and Cross diagram of the covalent bonds. Then, correspond the number of bonded and lone pairs to the molecule characteristics below:
Linear - 2 double bonds, bond angle of 180.
Trigonal Planar - 3 bonded pairs, bond angle of 120.
Tetrahedral - 4 bonded pairs, bond angle of 109.5.
Octahedral - 6 bonded pairs, bond angle of 90.
Pyramidal - 3 bonded pairs and 1 lone pair, bond angle of 107.
Non-linear - 2 bonded pairs and 2 lone pairs, bond angle of 104.5.
15. Hello!
I'm doing edexcel chemistry
Does anyone have any notes or link to videos on naming organic compounds? Or is someone able to explain it? I'm so bad at this yet everyone tells me how easy it is!
16. HELP ME SOMEONE AS

HElp me with the equation

and state and explain any difference between the two spectra

Thanks
Attached Images

17. Anyone have any useful material on Ozone depletion ? and Module 4 resources in general ?
18. (Original post by chantellerose)
Hello!
I'm doing edexcel chemistry
Does anyone have any notes or link to videos on naming organic compounds? Or is someone able to explain it? I'm so bad at this yet everyone tells me how easy it is!
Yes.
Here are some links for help with naming organic compounds
http://www.chemguide.co.uk/basicorg/...ons/names.html

And afterwards, ypu can practice with quizzes on this link

http://www.chemguide.co.uk/basicorg/...ons/names.html

The trick with nomenclature is to practice.I also used to be horrible at nomenclature and failed my nomenclature class test.But then I did tons of organic chemistry and nomenclature, so after a while it just became second nature to me.
You MUST be good at nomenclature or else you will FAIL organic chemistry part of AS Chemistry, since alot of the questions you msut be able to draw or identify the organic compounds mentioned in the question.
Practice make sperfect.Either you conquer nomenclature or it will conquer you.
19. Ahh, this could be useful, I jsut posted another thread before i came across this one!

I'm resitting OCR F322 and am just working on some revision posters, but I can't find my notes from last year on all the different mechanisms I need to know, the only one I can remember for certain is Radical Substitution but I know there's more!

If someone could remind me of the others I'd be really grateful!

Thank you!!
20. (Original post by Abby_W31)
Ahh, this could be useful, I jsut posted another thread before i came across this one!

I'm resitting OCR F322 and am just working on some revision posters, but I can't find my notes from last year on all the different mechanisms I need to know, the only one I can remember for certain is Radical Substitution but I know there's more!

If someone could remind me of the others I'd be really grateful!

Thank you!!
It is split into 4 modules
Module 1 (Basic organic chemistry concepts and hydrocarbons):
Nomenclature, Subsitution reactions,Isomers and stereoisomers,Polymers,Atom economy and Percentage Yield,Alkenes (The reactions, properties,its double bond and uses),Alkanes and everything I mentioned for alkenes apply to its except the double bond bit,Fossil fuels,Bond fission , and petroleum.

Module 2 (Alcohols,halogenoalkanes and analysis) :
Alcohol and their uses
Reactions of alcohols
Oxidising Alcohols
Esterifiication and Esters
Halogenoalkanes
Infrared spectroscopy and Mass spectroscopy

Module 3(Energy)nthalpy Changes
Bond Enthalpies
Measuring Enthalpy Changes
Hess Law
Reaction rates and collision theory
Catalysts
Reversible reactions
Boltzmann Maxwell Distribution
Chemical equilibrium
Equilibrium and Industry
Haber process

Module 4 (Resources):
The greenhouse effect and global warming(Learn the link between the two and remember ENHANCED greenhouse effect causes global warming)
Climate change
The ozone layer
Ozone depletion
Green chemistry
Air pollution
CO2,from villain to saviour(Hint:Basically just learn CO2 uses in Industry and how its obtained as a byprodut of fermentation).
Hope this helps

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