Edexcel - Chemistry Unit 2 - 4 June 2013

Thank you Zoey! I sort of understand that bit, its just when it gets a bit more complicated i.e. how to find the lone pairs in the 1st place haha.

Thank you Zoey! I sort of understand that bit, its just when it gets a bit more complicated i.e. how to find the lone pairs in the 1st place haha.

Lone pairs=( group number - number of electrons used up in bonding )/2
For example ammonia NH3 is in group 5 and so has 5 outer electrons.. out of these 3 are used in bonding. hence the lone pairs = (5-3)/2 = 1 lone pair

so as it has one lone pair and three bond pairs ..and the lone pair-bond pair repulsion is more than bond pair-bond pair repulsion it makes an angle of 107

the 107 angle is 2.5 less than the expected tetrahedral angle which is 109.5 because of the lone pair in it.
http://www.meta-synthesis.com/webbook/45_vsepr/balloon3.jpg

Definition of allotropes?


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Thanks for this. What about SO2? How do you fins how many electrons are used for bonding?

And in the above website for SCL4, how is it that sulfur has more than 8 electrons in a shell?

Different structural forms of the same element existing in the same physical state. ?

Definition of allotropes?


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http://diewissenschaft.wiki.hci.edu.sg/file/view/sulfur_dioxide.png/299205074/sulfur_dioxide.png

here's the dots and cross for SO2.
cross for Sulphur, dots for oxygen
& 2 bond pairs, 2 lone pairs, hence, the V-shaped angular shape

My problem is with shapes of molecules and ions. I need to know if there is a definite list of what to know or is there some way of knowing the shapes. I know the shapes of molecules which don't have lone pairs. But molecules with lone pairs is the problem for me how do you how many lone pairs are there in molecules like SO2? I don't know how to draw dot and cross diagrams for those types of molecules. Please help someone!!!

That dot and cross diagram of SO2 makes a lot more sense to me

I sometimes see sulfur dioxide like this:

http://1.bp.blogspot.com/_Z60kzbFyxFM/TB9ukVO6YsI/AAAAAAAAADc/I8LDqfJIx4s/s1600/apes3.png

I even saw on chemguide SO2 shown with two double bonds

SO2 has double bonds in it.

But does it have two or one ?

I see both O-S=O
&
O=S=O

Looking forward to this exam, generally speaking, it's easier if you've already done/doing A2. I need 105 ums in this exam for my A overall in chem, hopefully I can pull this off

If anyone has any questions, just post them here, the others or myself will be able to help.

Um.. how much would that make if we're considering out of 80, and not 120?

We can't say yet, because the grade boundaries haven't been out yet!!!




I need to aim for 70/80 marks, to be guaranteed of 105, but depending on the grade boundaries of course!

Yeah I meant the "estimated" value haha well good luck