I am having trouble understanding dipole moments. I can't figure out why that a tetrahedral CF4 molecule, trigonal planar SO3 molecule and a octahedral H2SF4 molecule are non-polar while a H2CF2 is polar? I hope I explained that well and thanks!
For CF4, think of it this way.
There is a dipole between each C and F since the electronegativities are different (C abouat 2.1 and F about 4.0). BUT CF4 is a tetrahedral molecule and the symmetry of the tetrahedral shape cancels the resultant dipole moment and the dipole moment of the molecule is zero. It may be easier to see with the SO3 since that is trigonal planar. Let dots represent oxygens.
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You can see the symmetry of the triangle. With S in the middle of the triangle, bonds from S to O have a dipole moment but the resultant is zero for the overall molecule. Same thing for octahedral. It would help if we could draw structures on the computer but the boards aren't so equipped. Be sure to follow up if you don't get it but please explain exactly what you don't understand.
Well from my very limitted knowledge of organic chemistry... The first three molecules you mentioned are completely symmetric in the distribution of the Hs Os and Fs about the carbon. With the H2CF2 however you have a tetrahedral molecule in which the Fs occupy one side of the molecule and the Hs the other side. Since the Fs attract the electrons more strongly than the Hs, the F side of the molecule is more - creating the dipole moment. To help visualize this google search molecular geometry and find a picture of the tetrahedral configuration. As you will see any location of the Fs and Hs results in this unsymmetric configuration. Hope this helps.
I'm sorry that I wasn't too clear. I understand that if all dipoles cancel then that molecule is non-polar but what I don't understand is how they cancel? Is it all based on symmetry and if it is; does the directions of the electronegativity have to pointing in the same direction when using symmetry?
yes and yes. Thus, all the bonds are equal in CF4. CF3Cl would have a dipole moment, as will CF2Cl2 and CFCl3. But CCl4, CF4, CH4, and CI4 will not. For octahedral, MX6 will be symmetrical but MX5Y will not. MX6 will not have a dipole moment because of the symmetry and all of the M-x dipoles canceling but all of the small individual M-X won't cancel when we have 5 M-x and 1 M-y for the MX5Y molecule. The symmetry thing is how we know H2O is not a linear molecule. If it were linear, as in H-O-H the the individual H-O dipole would cancel the O-H dipole and the result would be zero for H2O. BUT we can measure a dipole moment for H2O which means it must NOT be linear. In fact, the H2O molecule is quite easy to see how the symmetry makes the dipoles cancel if the molecule is linear.
Thanks, to both of you, you helped me out a lot! Now I'll be able to pass the "lovely" Chem. quiz on Tuesday! Have a g'night.
It just dawned on me what you meant by direction and my answer of yes may or may not be on the mark depending upon how you look at it. Look at the H2O molecule again.
The H-O-H linear arrangement has a slight + charge on the left H and a slight negative charge on the O. Mark that on a sheet of paper. Then on the other side, we have a another slight - on O and the H is +. Now draw an arrow on the left side going from - to + and on the other side another arrow going from - to +. See the arrows go in opposite directions so their effect cancels.
That is what I meant by direction.
Good luck on the quiz.
To understand why certain molecules like CF4, SO3, and H2SF4 are non-polar while H2CF2 is polar, we need to consider the concept of dipole moments and the molecular geometry of these molecules.
A dipole moment is a measure of the separation of positive and negative charges within a molecule. It arises when there is a significant difference in electronegativity between the atoms involved in a covalent bond. Electronegativity is the ability of an atom to attract electrons towards itself in a chemical bond.
In molecules with symmetrical geometry, the individual dipole moments can cancel out, resulting in a non-polar molecule. This cancellation occurs when the dipole moments point in opposite directions and have equal magnitudes.
Let's analyze each molecule you mentioned:
1. CF4 (tetrahedral geometry): In CF4, each C-F bond has a dipole moment because fluorine is more electronegative than carbon. However, the molecule has a tetrahedral geometry with the carbon atom at the center and four fluorine atoms surrounding it. The arrangement of the fluorine atoms in a symmetrical manner cancels out the individual dipole moments. As a result, CF4 is non-polar.
2. SO3 (trigonal planar geometry): In SO3, the sulfur atom is surrounded by three oxygen atoms in a trigonal planar arrangement. Each S-O bond has a dipole moment. However, the symmetric arrangement of the oxygen atoms cancels out the individual dipole moments, resulting in a non-polar molecule.
3. H2SF4 (octahedral geometry): In H2SF4, the sulfur atom is surrounded by four fluorine atoms and two hydrogen atoms in an octahedral arrangement. Similar to the previous cases, the symmetric arrangement of the fluorine and hydrogen atoms cancels out the individual dipole moments. Hence, H2SF4 is a non-polar molecule.
4. H2CF2 (tetrahedral geometry): In H2CF2, the carbon atom is bonded to two hydrogen atoms and two fluorine atoms. The arrangement of the atoms is not symmetrical as the hydrogen atoms are on one side and the fluorine atoms on the other side of the carbon atom. Fluorine is more electronegative than carbon, resulting in a polar C-F bond with a dipole moment. Since the molecule is not symmetrical, the individual dipole moments do not cancel out, and the molecule has an overall dipole moment. Therefore, H2CF2 is a polar molecule.
In summary, the symmetry of the molecular geometry plays a crucial role in determining whether a molecule is polar or non-polar. Non-polar molecules have symmetrical arrangements of atoms that cancel out the individual dipole moments, while polar molecules have an asymmetrical arrangement that leads to a net dipole moment.
Yes, that's correct! In a molecule like H2O, the dipole moments of the individual bonds (H-O) do not cancel out because the molecule is bent or V-shaped due to the lone pairs of electrons on the oxygen atom. The dipole moments of H-O bonds are not directly opposed to each other, resulting in a net dipole moment for the molecule.
On the other hand, in molecules like CF4, SO3, and H2SF4, the dipole moments of the individual bonds (e.g., C-F, S-O, S-F) do cancel out because of the symmetrical arrangement of atoms around the central atom. In tetrahedral CF4 and octahedral H2SF4, the dipole moments of the individual bonds point towards the central atom and are equally distributed, resulting in a net dipole moment of zero. In trigonal planar SO3, the dipole moments of the individual bonds point towards different directions and again cancel out, resulting in a non-polar molecule.
It is crucial to consider the symmetry and arrangement of atoms in a molecule to determine if the dipole moments cancel out or not. If the dipole moments of all the individual bonds do not cancel out each other, the molecule will be polar. If they cancel out, the molecule will be non-polar.