How do I know which bonds are polar or not?

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Et Tu, Brute?
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#1
Report Thread starter 7 years ago
#1
I know you need to know the electronegativity, but how do I know that?

I have got by thus far from the electronegativity table (eg. F=4.0) but given that this hasn't appeared in my lecture notes or workshops I'm thinking that my lecturer has said how to find it but I've missed it.

For example PCl3 I said was no polar because I didn't know the electronegativities of P to compare them to Cl. As I wouldn't have this table with me in the exam there is not point in using it.

How do I know which bonds will be polar?
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Secret.
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#2
Report 7 years ago
#2
(Original post by Et Tu, Brute?)
I know you need to know the electronegativity, but how do I know that?

I have got by thus far from the electronegativity table (eg. F=4.0) but given that this hasn't appeared in my lecture notes or workshops I'm thinking that my lecturer has said how to find it but I've missed it.

For example PCl3 I said was no polar because I didn't know the electronegativities of P to compare them to Cl. As I wouldn't have this table with me in the exam there is not point in using it.

How do I know which bonds will be polar?

Are you given a periodic table in the exam? Something like this may help Image
(http://www.chemguide.co.uk/atoms/bon...lectroneg.html)
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Et Tu, Brute?
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#3
Report Thread starter 7 years ago
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(Original post by Secret.)
Are you given a periodic table in the exam? Something like this may help
(http://www.chemguide.co.uk/atoms/bon...lectroneg.html)
Yeah I've got a periodic table, the thing is though, say for the PCl3 example I gave, both are period 3 but Cl is group 7 so it is more electronegative. However I don't know how much more electronegative. For example H is 2.1 and C is 2.5, H-C bonds are considered essentially non-polar.

Then of course there is possible combinations like Oxygen and Chlorine or Bromine which aren't in the same period.

I'll just have to learn the electro-negativities of the elements. But I feel like this is on power with using a calculator for maths questions designed for non-calculator papers, sure you get the answer, but the understanding isn't there.

Surely there is some sort of general way to work these out?
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TSR561
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#4
Report 7 years ago
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(Original post by Et Tu, Brute?)
Yeah I've got a periodic table, the thing is though, say for the PCl3 example I gave, both are period 3 but Cl is group 7 so it is more electronegative. However I don't know how much more electronegative. For example H is 2.1 and C is 2.5, H-C bonds are considered essentially non-polar.

Then of course there is possible combinations like Oxygen and Chlorine or Bromine which aren't in the same period.

I'll just have to learn the electro-negativities of the elements. But I feel like this is on power with using a calculator for maths questions designed for non-calculator papers, sure you get the answer, but the understanding isn't there.

Surely there is some sort of general way to work these out?
After a few questions you'll get the hang of it. The halogens tend to be the electronegative part of the question being asked. In no way do you need to know specific values by heart.
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Et Tu, Brute?
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#5
Report Thread starter 7 years ago
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(Original post by TSR561)
After a few questions you'll get the hang of it. The halogens tend to be the electronegative part of the question being asked. In no way do you need to know specific values by heart.
test is on Friday sadly, so I've not got much time.

Then of course there is the shape to factor in as well. For example the difference between oxygen and fluorine is 0.5, so essentially non-polar. Yet oxygen difluoride is a polar molecule.
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