How do you know which molecules can have a dipole moment?
you must know their SHAPES (draw them) and see the atoms linked to the central atom. THE DIPOLE MOMENT IS A VECTORAL QUANTITY. TWO VECTORS OF EQUAL SIZE ALIGNED OPPOSITE EACH OTHER WILL PROVIDE ZERO . it’s not that.
See now,
1. CO2 –(O=C=O)—- linearly, one oxygen to the left of the carbon and one to the right. oxygen being more electronegative than carbon, it withdraws the electron density to itself, causing the dipole moment O<-----C , da mesma forma, outros oxigênios gostarão de C------>O. alignment of dipole moments is like O<-----C----->O. The two dipole moments are aligned opposite each other and have the same magnitude. so that the resulting vector addition law of these will be zero.
2. SO2 is bent or V-shaped like water. The S=O bond is polar and the dipole moment exists as S -> O for both sulfur-oxygen bonds. but this time the molecule has a curved shape. the two EQUAL vectors are aligned at a certain angle, so the resultant will not be zero, but a certain value (calculated from the vector addition law).
3. carbon tetrachloride = tetrahedral form, has all the chlorines attached to it. therefore each C—->Cl bond is polar, positively charged carbon and negative chlorine. if i could draw the structure here.
4. BF3 is a trigonal planar molecule with B—>F bonds 120 degrees apart. all vectors are equal in magnitude. let’s say these three vectors are V1, V2 and V3 resp. . sometimes, resulting from two vectors is nothing more than a vector of magnitude equal to these aligned, sometimes opposite to the third that we left the first. thus, this resultant and the third vector being equal and aligned in the opposite direction will give the resultant global dipole moment equal to zero.
if you still have a problem with any of these, you can ask again, i’ll try 2 help. I think students usually have trouble with molecules that are tetrahedral in shape, but you’re trying to make a shape and figure it out.
yes you can easily understand the concept if you have a molecular model defined (or if you do it using balls or clay and sticks) make a tetrahedral molecule you will see that two vectors give a resultant in one direction and the other two in the other direction. and, finally, these resultants add up to give zero dipole moment. I hope you understand. Good luck
Chemistry of Dipole Moment Calculation