Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: d1wedemeier on June 12, 2005, 05:34:40 PM
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Does the issue of having three elements combined in a molecule change the electronegativity calculation?
Concerning the molecule CHCl3
The difference between C and H is 2.4-2.1=.3
The difference between C and Cl is 2.5-3.0=.5
The text book offers no examples of this situation for me to go on.
I think that all the bonds should be considered polar covalent or is there and exception I need to be aware of?
How do determine the polarity of the molecule? From what I've read it leads me to believe that is would be a polar molecule, am I correct?
Thanks ???
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Here is a better question. Do polar bonds always lead to polar molecules?
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No, as in the case of CF4, polar bonds CAN lead to non polar molecule.
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Chloroform is a polar molecule.
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d1wedemeier - I'm going to explain one way of determining polarity at the high school level
Did you learn how to draw lewis structures or how to determine the shape of a molecule?
One way of estimating polarity ( I stress estimating )
1) draw shape of the molecule
2) use electronegativity to determine the type of bond
3) what makes a polar molecule is that the partial charges are not in the same spot / what makes a nonpolar molecule is that they are in the same spot
so carbon tetrachloride has four polar bonds, but the partial + and - charges are both centered on the C. The C has the partial + and the Cl have the partial -s. The average position of the - is on the C. No pole or nonpolar
with carbon trichloride the partial + and - are at different positions, thus, there is a "pole" and it is polar
This technique is only useful on small molecules, on more complex ones it becomes more difficult to determine. Large molecules can actually have polar and nonpolar regions - for example integral proteins that span the nonpolar region of a plasma membrane and stick out into the hydophilic cytoplasm.