μdiatomic=Q×r(13.3.2)

(13.3.2)μdiatomic=Q×r

This bond dipole is interpreted as the dipole from a charge separation over a distance rr between the partial charges Q+Q+ and Q−Q− (or the more commonly used terms δ+δ+ - δ−δ−); the orientation of the dipole is along the axis of the bond. Consider a simple system of a single electron and proton separated by a fixed distance. When proton and electron close together, the dipole moment (degree of polarity) decreases. However, as the proton and electron get farther apart, the dipole moment increases. In this case, the dipole moment calculated as (via Equation 13.3.213.3.2):

μ=Qr=(1.60×10−19C)(1.00×10−10m)=1.60×10−29C⋅m(13.3.3)μ=Qr=(1.60×10−19C)(1.00×10−10m)(13.3.3)=1.60×10−29C⋅m

The Debye characterizes size of dipole moment. When a proton & electron 100 pm apart, the dipole moment is 4.80D4.80D:

μ=(1.60×10−29C⋅m)(1D3.336×10−30C⋅m)=4.80D(13.3.4)

μ=(1.60×10−29C⋅m)(1D3.336×10−30C⋅m)(13.3.4)=4.80D

4.80D4.80D is a key reference value and represents a pure charge of +1 and -1 separated by 100 pm. If the charge separation were increased then the dipole moment increases (linearly):

• If the proton and electron were separated by 120 pm:

μ=120100(4.80D)=5.76D(13.3.5)(13.3.5)

μ=120100(4.80D)=5.76D

• If the proton and electron were separated by 150 pm:

μ=150100(4.80D)=7.20D(13.3.6)

(13.3.6)μ=150100(4.80D)=7.20D

• If the proton and electron were separated by 200 pm:

μ=200100(4.80D)=9.60D(13.3.7)

The dipole moment is the product of the (partial) charge and the distance. You can have a very large dipole moment in zwitterions. These are formed by aminoacids in water at special pH values. If you want a dipolar compound that exists in the vapour phase, NaCl or KBr are good candidates, or organic molecules like CF3H.