Sketch a picture of the polarized molecule, showing the HCl molecule and a dipole model of the molecule.
Dipole model of an HCl molecule.
The magnitude of the dipole moment of the molecule is defined as
where is the magnitude of each charged particle in the dipole and is the separation of the charged particles. In this case, the magnitude of the charge of each particle in the dipole is , thus
Solving for the partial charge of each atom gives
Note that this is less than the magnitude of the charge of an electron ( ). That's why it's called a partial charge.