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***2013 LC Chemistry Before/After***
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aoifemcg94 wrote: »I know that bit but yano sometimes when ya do that it doesn't always tell if it's polar or non polar until you draw it out? If you get what im saying
When you draw it out...
-If its linear it will always be polar...however...
Sometimes in planar molecules the positives and negatives cancel each other out if you draw a line connecting them out through the centre and they all meet, then its non polar as they cancel eachother out!0 -
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outnumbered wrote: »Do you know them short questions where it asks the shapes of the molecules?
What the best way to learn these?? I never know the answer
Ok my trick:
Learn off the shapes of
H20-Vshaped
NH3-Pyramidal
Co2-Linear
Ok then on the day of the exam use a log table and periodic table...to see if your elements and numbers match any of the above...
For example...
H2S (idk if thats right or whatever just for the sake of an example!)
Now my h2 is like h2o.....and s is directly below oxygen therefore it has the same valency so H2S must be v shaped too!0 -
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Nothing's to say linear molecules can't be non-polar, take CO2 for example, the centre of positive and negative charge will be on the Carbon atom so they cancel out, thus it's non-polar.
I don't really know of how to simplify it, I just draw them out.
V-shaped will be polar, as will pyramidal (I think), tetrahedral the charges will overlap generally, planar triangular will overlap if all of the atoms attached to the central atom are the same. 0 -
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Nothing's to say linear molecules can't be non-polar, take CO2 for example, the centre of positive and negative charge will be on the Carbon atom so they cancel out, thus it's non-polar.
I don't really know of how to simplify it, I just draw them out. V-shaped will be non-polar, as will pyramidal (I think), tetrahedral the charges will overlap generally, planar triangular will overlap if all of the atoms attached to the central atom are the same.
Ok thanks I think I get it now cheers fellow chemistry students! 0 -
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Nothing's to say linear molecules can't be non-polar, take CO2 for example, the centre of positive and negative charge will be on the Carbon atom so they cancel out, thus it's non-polar.
I don't really know of how to simplify it, I just draw them out. V-shaped will be non-polar, as will pyramidal (I think), tetrahedral the charges will overlap generally, planar triangular will overlap if all of the atoms attached to the central atom are the same.
V-shaped will ALWAYS be polar.
Pyramidal will also be polar.
Tetrahedral will be non-polar.
Triangular planar will be non-polar.0 -
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Tetrahedral will be non-polar.
Triangular planar will be non-polar.
That's true in LC Chemistry terms, however in the wide world of Chemistry I'm fairly certain this won't always be the case which is why I didn't say always.
But yes for anyone not sure in terms of the exam, learn what this guy said!
Also I meant to say polar for v-shaped/pyramidal, that was a typo. 0 -
That's true in LC Chemistry terms, however in the wide world of Chemistry I'm fairly certain this won't always be the case which is why I didn't say always. But yes for anyone not sure in terms of the exam, learn what this guy said!
As you can see, that's why I didn't say always for those either
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Am I the only pesron who feel lost ?
I read your posts about polar and shapes and completey felt my studying was a waste of time
For me I would calculate the electronegativity of the compound and determine if it's polar or not
For shapes
I listed all of them in a Paper
2 atoms = linear
3 atoms :
A) linear if they don't have lone pairs
V- shaped if they do
4atoms :
A) triangular planar (no lone pairs) pyramidal (lone pairs)
5atoms: tetrahedral
Please tell me this works right with every thing! (* I might mixed some of them!)
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Really scared for this exam! I need at least an A2 and the strict marking scheme adds so much more pressure! and to make it worse I've lost out on two days study because I was in hospital!! Was so close to discharging myself!! Can anyone help me with what i should focus on? I've done all the titrations that can come up on Question 1 and the organic practicals.. I know organic chemistry and atomic theory really well..
What else is crucial to know?
At this point go for the ones that always come up: equilibrium, option A/B question 11, atomic theory/ionization energies. Know your experiments by heart 0 -
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D'you know, I think the organic question will be both ethanal AND ethanoic acid, like they did with ethene and ethyne 2 years ago. Just sayin'.
I think I'll cry if a full question on water doesn't come up. This is the first exam I'm actually panicking a bit for, knowing the marking scheme will be a curse
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