AQA Chem Unit 1 May 22nd 2015 *OFFICIAL THREAD*

Original post by _minasan

1. State number of bonding pairs and lone pairs of electrons.
2. State that electron pairs repel and try to get as far apart as possible (or to a position of minimum repulsion.)
3. If there are no lone pairs state that the electron pairs repel equally
4. If there are lone pairs of electrons, then state that lone pairs repel more than bonding pairs.
5. State actual shape and bond angle

^ From chemrevise

Original post by samwillettsxxx

State the bonding pairs and if it has any lone pairs and then the bond angle and any repulsion

thankss

Reply 982

badaman

Original post by GabrielSmith1998

There is an equation you can use.
get the group number of the element that there is only one atom (IE in NH3 it would be Nitrogen which is 5) of and add to it the number of electron pairs (in NH3 it would be 3, you can just use the number of other atoms in the molecule too if that makes sense). After, subtract the charge and then divide the number by 2. This gives the bonding pairs, and then subtract bonding pairs from electron pairs for lone pairs.

I just noticed that you probably meant why do molecules get into their specific shapes.
-Bonding pairs repel each other equally.
-Bond angles will be equal IF NO LONE PAIRS ARE PRESENT. At least I think that is the case.

~Ta x

Reply 983

kalo0osh

Original post by Prem1

Hey, could you like share the type of questions in the exam, hopefully to the best of your memory, after you've done it
thankyou

I'm sorry to say but my exam board is edexcel not AQA.I thought this thread is about is about the edexcel exam.Sorry :colondollar:

Reply 984

Original post by sleepisheaven

HF Has H bonding

The rest only have weak vdw.

As molecules become larger/more electrons/greater Mr (the ones with vdw) the vdw forces between molecules become stronger.

Posted from TSR Mobile

That makes sense but why don't the other molecules have permanent dipole dipole? :frown:

Reply 985

dripper

14

??

Original post by dripper

Can we do dots for lone pairs instead of this stupid balloon?

Reply 986

akereem100

10

Jan 2013 ms say reject simple covalent for OF₂ and the answer is simple molecular. Is it always like that or is OF₂ special case?

Reply 987

Original post by Boundless_x

That makes sense but why don't the other molecules have permanent dipole dipole? :frown:

Electronegativity difference not enough for permanent dipole-dipole.

Reply 988

Original post by dripper

??

Have no idea, we've always been taught to draw the balloons

Reply 989

Amyjonesx

how do you calculate limiting reagent???

Reply 990

Original post by JRN-95

Electronegativity difference not enough for permanent dipole-dipole.

Can you give me some examples of molecules with permanent dipole dipole if possible thanks :smile:

Reply 991

GabrielSmith1998

7

Original post by Amyjonesx

how do you calculate limiting reagent???

Sorry this is the AQA thread!

Reply 992

Original post by akereem100

Jan 2013 ms say reject simple covalent for OF₂ and the answer is simple molecular. Is it always like that or is OF₂ special case?

Always say simple molecular as it's the correct term, but lenient MS may give mark to simple covalent. Better safe than sorry though.

Reply 993

Amyjonesx

Original post by GabrielSmith1998

Sorry this is the AQA thread!

do we not need to know this for AQA?? yes!! what a waste of time I have been trying to figure it out for one hour!

what about theoretical yield?

Reply 994

randoms132

Original post by akereem100

Jan 2013 ms say reject simple covalent for OF₂ and the answer is simple molecular. Is it always like that or is OF₂ special case?

Questions says 'crystal' so it can either be Giant ionic lattice, Metallic, Macromolecular or Simple molecular so its pretty clear which one it'll be
:smile:

hope it cleared things up

Posted from TSR Mobile

Reply 995

Kloekayne

Any advise on how to pass the moles section in the paper? I'm really bad at the calculations

Posted from TSR Mobile

Reply 996

Original post by Boundless_x

Can you give me some examples of molecules with permanent dipole dipole if possible thanks :smile:

HCl, CH3Cl but you won't be expected to give examples out of nowhere they usually give you some info.

Reply 997

Amyjonesx

probably should know this by now but what is the difference between having dipole dipole and van der waals?

Reply 998

Original post by JRN-95

HCl, CH3Cl but you won't be expected to give examples out of nowhere they usually give you some info.

But in the previous question, why can you not say there is permanent dipole dipole in HCl? Why are we only supposed to talk about van der waals forces?

Reply 999