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

Hi electronegatity increases as you go across the periodic table and decreases as you go down the group
If an atom has more electrons than another, you know it is more electronegative because the outer shell is further from the nucleus therefore easier to attract

It should be pyramidal
Not tetrahedral
Right? :/

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It would have 3 bonding pairs and 1 lone pair so would be a pyramidal

When drawing shapes of molecules why is NHf2 a tetrahedral??? ... :/

Ahah I don't really know ...The answer said trigonal pyramid or tetrahedral ...I just don't get why isn't trigonal planar?? :/

It would be trigonal bypyramidal because the N can have 5 bonds to it due to having no charges but only 3 will bond leaving 2 lone pairs. However I'm not sure if this would then mean it is just called bent. What paper is it from? I remember the question being asked.

It wouldn't be trigonal bi pryramidal it will be trigonal pyramid 2 different things note that!

It would be trigonal bypyramidal because the N can have 5 bonds to it due to having no charges but only 3 will bond leaving 2 lone pairs. However I'm not sure if this would then mean it is just called bent. What paper is it from? I remember the question being asked.

Is trigonal pyramid the same as trigonal planar?

It wouldn't be trigonal bi pryramidal it will be trigonal pyramid 2 different things note that!

No it isn't. Trigonal planar has 3 bp with no lp The angle between the bonds are 120 degrees

Trigonal pyramid is a subshape to a tetrahedral, it has 3bp and 1lp, with bond angle 107 degrees

Jun11 3bi I wrote pyramidal and got the mark but can't seem to understand why AQA accept tetrahedral?

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The mark scheme for this question also allows tetrahedral however so it wouldn't matter which you put

Yeah but you said trigonal planar, trigonal planar is not a tetrahedral & trigonal bypyramid is also not a tetrahedral. Trigonal pyramid however is the actual shape of the basic shape of a tetrahedral.

AQA accept tetrahedral because the basic shape of a trigonal pyramid, tetrahedral and V-Shape is a tetrahedral. The specific shapes are the actual shapes eg V-Shape etc. But with the bp and lp (if we pretend each lp makes a bond) they all make 4bp and hence have 109.5degree bond angle. The angle is decreased by 2.5 degrees per lone pair.


AQA accept tetrahedral because some people may quote the basic shape which is tetrahedral and is therefore correct. Although not strictly what they are asking for.

Heya! Can someone help me with this question? I just don't know how to get the answer.

1.40g of an alkene gave 3.77g of a dichloroalkane on reaction with chlorine. What is the molecular formula of the alkene?

Hi if you don't know weather it has lone pairs it always helps me to draw the dot and cross diagram to help

It would be trigonal bypyramidal because the N can have 5 bonds to it due to having no charges but only 3 will bond leaving 2 lone pairs. However I'm not sure if this would then mean it is just called bent. What paper is it from? I remember the question being asked.

Ohh that's a good idea thanks! So do lone pairs not affect the name only the bond angle??