# Dipole in physics and Chemistry

1. Sep 24, 2004

### Simonnava

Here is my concern,

In my physics class I learned that a dipole moment always goes from the - charge to the + charge. But as I was reading my Organic Chemistry book, it says that the dipole goes from + to -! how can this be?

P = Qd

Simon

2. Sep 24, 2004

### Sirus

A chemical dipole is the vector resultant of the vectors of the charges present. For example, a V-shaped molecule such as water has two charge vectors pointing from each hydrogen to the central oxygen because of the oxygen's higher electronegativity; therefore, the resultant dipole points straight through the oxygen (bisects the smaller angle between the two bonds with hydrogen). Not sure about physical dipoles or that formula. Hope this helps.

3. Sep 24, 2004

### marlon

This is convention. Mostly a dipole vector goes from - to +. Now what your chemistry book is trying to say is that a dipole arise because the + and - charges are not homogeneous. For example when two electrodes are placed into a neutral specimen containing charged particles (both + and - charges) then when a current is applied for example the positive charges will evolve to one side (or plate if you will) of the electrode and the negative charges will go to the opposite direction. because of this new "configuration" the charges are placed into two groups : a positive group on the one side and a negative group on the other side. this difference in charge distribution causes the dipole.

The formula is right for the magnitude of the electrical dipole. Normally it is
p=Qd where the d-vector goes from the negative to the positive charge and denotes the distance between them...

marlon