POLAR OR NONPOLAR Y OR Y NOT?

November 13, 2004 at 2:36 pm #197

Participant

HOW CAN U ACTUALLY DETERMINE WHETHER A MOLECULE IS POLAR OR NOT?
IT IS EASY IF SIMPLE MOLECULE LIKE CCI4 BY KNOWING THE RESULTANT DIPOLE BUT WHAT IF COMPLEX BIG MOLECULE LIKE GLUCOSE.AS WHAT I KNOW EVERYONE SAYS THAT ORGANIC MOLECULE ARE ALL NONPOLAR WHAT U COULD DO TO SHOW THIS I KNOW IT CAN DISSOLVE INWATER BUT THATS NOT A STRONG EXCUSE.

OK TAKE FOR A MONO SUGAR FOR EXAMPLE Y IT IS NOT POLAR IT HAS HYDROXYL GROUP CARBONYL GROUP?AND LIPID HOW DO U CLASSIFIED IT BCAUSE IT HAS POLAR HEAD BUT OVERALL BCAUSE IT TAIL IS NON SO IT IS NONPOLAR TOO?

I HAVE THIS PROBLEM TO DETERMINE POLARITY PLS HELP

November 15, 2004 at 6:08 pm #18647

FutVeterinarian

Participant

😯 WOW! I’m only in Biology I! I have NO idea what you’re talking about! 😯

November 15, 2004 at 7:50 pm #18650

biostudent84

Participant

Build a ball and stick model of a molecule. If there is ANY point on the molecule where you can cut it with a saw and have two identical pieces, the molecule is nonpolar. If you cannot do this, then it is safe to assume the molecule is polar.

H H
| |
H–C==C–H

Is nonpolar….you would have 2 CH2’s.

H H
| |
H–C==C–OH

Is polar…you cannot cut it and get two identical pieces.

Please keep this in mind that this is a rule of thumb, but it will work in most cases.

January 21, 2005 at 4:15 am #19077

mith

Participant

I’ve always wondered how a simple symmetrical molecule is nonpolar. Shouldn’t it be 3D and rotationally symmetrical to have equal charges on all facets?

January 21, 2005 at 6:29 am #19084

biostudent84

Participant

Please give an example of one of these symmetrical molecules…

January 22, 2005 at 3:56 am #19092

mith

Participant

well ch4 has a 3d tetrahedral structure so that’s the 3d symmetrical nonpolar I was referring to but compare that to a a linear molecule in the form

x-o-x

wouldn’t there be some extra charges toward the top/bottom/ sides of the “o” that’s not occupied by a bonded atom?

January 22, 2005 at 8:08 am #19101

2810712

Participant

WHy , do U think, one needs to determine whether the molecule is polar or not ?
I think , it helps us predict the behavior of the molecule . So, what would we do in confusing cases like lipid molecules is we will determine the behaviour of polar part and non polar part separately & then this will tell us how the molecule behaves.
hsg

April 25, 2005 at 1:30 am #21649

Charlene

Participant

➡ Polar Molecules include:
– diatomic compounds e.g. CO(g)
– any molecule with a single H e.g. HCL(g)
– any molecule with an OH at one end e.g. C2H5OH(l)
– any molecule with an O at one end e.g. H2o(l), OCl2(g)
– any molecule with a N at one end e.g. NH3, NF3(g)

➡ Nonpolar Molecules include:
– all elements e.g. Cl2(g), N2(g)
– most carbon compounds including organic solvents, fats, oils e.g. CO2(g), CH4(g)

❗ The symmetrical rule as mentioned earlier by biostudent84 is essential in determining whether a substance is polar or not. If the structural diagram is symmetrical, then it is nonpolar. If it is not symmetrical, then it is polar. However, there are exceptions to this rule. e.g. H2O is symmetrical, but it is polar. 😉

April 25, 2005 at 5:03 am #21653

mith

Participant

It might be symmetrical in the formula h0h but that doesn’t show the unshared pair.

April 25, 2005 at 3:16 pm #21672

James

Participant

Firstly, work out if the molecule has any dipoles, and then work out if these dipoles are ruled out due to symmetry- if not it is polar.

January 2, 2011 at 1:10 pm #102981

leftventricle

Participant

Lipids are amphiphillic, they have a hydrophilic head (polar) and hydrophobic tail (non-polar).

January 22, 2011 at 9:56 pm #103283

JackBean

Participant

quote mith:

It might be symmetrical in the formula h0h but that doesn’t show the unshared pair.

but the structural formula is not (symmetrical) 😉

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