Help With Dipole Moment Question

[comwiz72]

Hi, I'm stuck on a certain question in a tutorial sheet, and would appreciate a nudge in the right direction.

The problem is in one particular question to which I missed notes due to illness, and won't have time to copy up before they need handed in.

The question is on dipole moments:

The relative permittivity of xenon at S.T.P. (0C and 1 Atmosphere) is 1.001352. Estimate the magnitude of the dipole moment induced in each xenon atom when the gas is subjected to an electric field E of strength of 5 x 10^5 V/m

Avogadro's Number Na = 6.02 x 10^23
Volume of 1 mole of gas at S.T.P. = 2.24 x 10^-2
Permittivity of vacumn = 8.85 x 10^-12

If the equilibrium inter-nuclear separation r in a completely ionic molecule is 2.8 x 10^-10 metres, calculate its permanent electric dipole moment, and compare with the value obtained above.Like I said, I don't want the answer or solution, but I'm at a bit of a loss as to where to begin, and would appreciate a little explanation.

I've worked out the internuclear separation of the atoms, and I think I know where to go, but do I need to use the relative permittivity of the xenon to work out the electric field strength within the gas, then use the dipole moment calculation to get the result?

 

[Meir Achuz]

You are given E. Use the permittivity to find P (Polarization vector).
Then use P=np, where n is the number density of atoms to find the dipole moment p.

 

[comwiz72]

ah of course, using the susceptibility = permittivity - 1
thats what i was looking for, thanks, i just couldn't see it :P