Matter & Interactions 2nd ed. Practice Problems
Aaron Titus | High Point University
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2d40001     Dipole model of HCl     2d40001
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Question

 

The HCl molecule is polar with a dipole moment and a negative partial charge at the chlorine atom and a net positive partial charge at the hydrogen atom. From infrared spectroscopy, the bond length of a HCl molecule is calculated to be 0.13 nm. If you model the HCl molecule as a dipole of charges and separated a distance 0.13 nm, what is the charge in the model?

 



Solution

 

Sketch a picture of the polarized molecule, showing the HCl molecule and a dipole model of the molecule.


Figure: 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.