polarity question?

Question

how can i tell whether a molecule is polar or non polar?
thanks

Answer 1

you can tell if a molecule is polar by the difference in electronegativities, if the difference is between .5 and 1.7, then the molecule is polar. You can also draw the structures. Draw each atom in the molecule, like in a Lewis Dot Structure and draw arrows indicating direction of electronegativity. This means we will be predicting dipole moments.
Take for example a molecule with a central carbon, three chlorine atoms and a hydrogen atom.

So imagine with me, there will be an arrow pointing away from the central carbon to each Chlorine. This is because the arrow points to the more electronegative atom. We can ignore the C-H bond in this case because the difference is so small.
So to determine the dipole moment, you add up each individual vectors, there will be 3 in this case. Line the vectors up head to tail. The dipole moment for the molecule points from where you started to where you ended up , in this case



-------------------> --this is the overall dipole moment


Note that the molecule is polar and each vector represents a Cl atom.


Linear ex CO2

O=====C=====O
<------- --------->
When you add these together, head to tail, they will cancel each other out and there will be no dipole moment
<-------------
-------------> so the Oxygens on each side of the carbon at pulling at equal and opposite directions.


Really kinda confusing, hope it helps a little
if you need help, either by recognizing whether or not molecules are polar by a formula or by a dipole moment, you could check this out
Hope I didnt confuse you in any way, sorry If i did
good luck


sorry the link is http://preparatorychemistry.com/Bishop_molecular_polarity.htm

Answer 2

First, are the elements in the molecule different? If not, they have the same electronegativity, and so there is no dipole separation. Example: F2. F is the most electronegative element known, but if they're pulling against one another, sheesh!

Second, if the elements are different, is the molecule symmetrical? Carbon and oxygen are very different in electronegativity. But in carbon dioxide, O=C=O, they're pulling against one another. But in carbon monoxide, C=O, it's polar.

Answer 3

You need to know the bonds that it has and the shape of it H2O is polar because of its bonds and its shape because the charges are not distributed equally. CCl4 is not polar because of its shape the carbon in the middle and the 4 Cl surrounding it.