POLAR OR NONPOLAR Y OR Y NOT?

[porifera]

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

[FutVeterinarian]

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

[biostudent84]

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.

[mith]

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?

[biostudent84]

Please give an example of one of these symmetrical molecules...

[mith]

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?

[2810712]

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

[Charlene]

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.

[mith]

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

[James]

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.