Determine if a Molecule is Polar - Steps & Tips

[chemistry1]

Hi,

I know what are the steps to determine if a molecule is polar or not, but I'm having one small problem. When I have determined teh geometrical shape of my molecule and drew the vectors of the polar bonds that goes from the least electronegative atom to the most electronegative atom, how exactly do I add these vectors? I know that if the sum of my vectors give 0, I have a non polar molecule and if it doesn't then it's polar. But for some easy geometrical shapes I can easily add them, and for some others I don't know. For example, I may know from the beginning that the molecule is non polar because its lewis structure is symmetrical, but when it's time to show it using vectors, for some reason, I'm not able to do it. If I had the sp^3 shape (tetrahedron), and I know that the 4 vectors must give 0, this is where I get stuck.
Anyway, I need help! Thank you again.

 

[Borek]

This is a math problem, not chemistry.

http://en.wikipedia.org/wiki/Euclidean_vector

 

[chemistry1]

Well, I know how to add vectors but only if they're 2d...

 

[DrDu]

Well, you start adding the first and the second, the sum vector lying in the plane spanned by the two vectors. So the problem reduces to the two dimensional case.

 

[LudusRex]

Hello,

Thank you for reaching out. Determining if a molecule is polar can be a tricky process, but there are some steps you can follow to help you determine the polarity of a molecule.

1. Identify the central atom: The first step is to identify the central atom in the molecule. This is typically the atom that has the lowest electronegativity value.

2. Determine the molecular geometry: Use the VSEPR theory to determine the molecular geometry of the molecule. This will help you visualize the arrangement of atoms in the molecule.

3. Identify the polar bonds: Next, determine which bonds in the molecule are polar. A polar bond is formed when there is a difference in electronegativity between the two atoms in the bond.

4. Draw the vectors: For each polar bond, draw a vector from the less electronegative atom to the more electronegative atom. The direction of the vector should indicate the direction of the electron flow.

5. Add the vectors: Now, add all the vectors together. If the sum of the vectors is equal to zero, then the molecule is nonpolar. If the sum is not equal to zero, then the molecule is polar.

6. Consider the molecular symmetry: In some cases, even if the sum of the vectors is not equal to zero, the molecule may still be nonpolar due to its molecular symmetry. For example, if the molecule has a symmetrical shape like a tetrahedron, then the polar vectors may cancel out, resulting in a nonpolar molecule.

I understand that adding vectors can be challenging, but it is important to remember that the direction of the vector is what matters, not the length or magnitude. You can use a protractor to help you determine the direction of the vectors.

I hope this helps. If you continue to have trouble, I recommend seeking assistance from your instructor or a tutor. Keep practicing and you will become more comfortable with determining the polarity of molecules.

Best of luck!