why does an isolated atom not have a permanent dipole moment??????
An isolated atom such as?
A dipole consists of a pair of charges separated by some distance. Since the positive charge of the nucleus is very nearly concentric with the negative charge cloud of the electrons single atoms are not dipoles.
you are talking about an electric dipole. the OP might have been about a magnetic dipole. many atoms do have magnetic dipole moment (any atom with a spin will have a dipole moment). and many atoms have a small electric dipole moment too
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