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After a long research on electric polarization, here's what I understood (please correct if there are any misunderstanding):

In an atom (neutral), electrons are permanently moving around the nucleus (protons and neutrons). Each electron has an orbit. Electron cloud has the same barycenter of the nucleus. When an electric field is applied, electron cloud is deformed and the barycenters are no longer the same (the atom is polarized and similar to a dipole).

Does it mean that the electrons are no longer moving around the nucleus or/and they stop moving? If electrons still moving, what about the new orbits, are they the same or they are deformed and/or they barycenters are shifted ? How the new electrons motion is described ?

What I initially think, that most of the electrons moves in a cloud whose the barycenter is deviated from that of the nucleus, and the other electrons are still moving around it (the nucleus).

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The notion that electrons move in orbits (as once proclaimed by the now defunct Bohr atomic model) is no longer accepted by modern quantum physics. In that new model electrons occupy so-called atomic orbitals.

In this model it's impossible to predict the exact location of an electron and we can only calculate the probability of finding an electron in a specified spatial area of the atom. This is antithetical to well defined electron orbits.

Electrons do nonetheless still move 'around' the nucleus (as in: "in its vicinity" but not in well defined orbital paths) and remain susceptible to electrical fields or the electrostatic repulsion exerted by other electrons.

In an atom placed in a strong electrical field, the probability of finding the electron nearer to the positive side of the field increases. As the charge centres of the nucleus and the electron 'cloud' now no longer coincide, the atom is temporarily polarised. The polarisation is lifted when the electrical field is removed.

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  • $\begingroup$ so when the electron is nearer to the positive side of the field, does it mean that it (the electron) is still moving but no more around the nucleus (always near the nucleus but not around it) ? $\endgroup$
    – Sofiane
    Oct 23, 2016 at 1:26
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    $\begingroup$ It's still moving but on average the probability of finding it will be skewed towards the + side of the field. Forget about the notion of 'moving around the nucleus': it's a meaningless concept in QP. No knowledge of exact position means it's impossible to define 'around'. NO orbits! $\endgroup$
    – Gert
    Oct 23, 2016 at 1:30
  • $\begingroup$ 'around' doesn't necessarily mean an 'orbit', electron can randomly move around the nucleus without any defined orbit. Did you mean that even this hypothesis is invalid in QP ? or 'around' in that sens can be acceptable in QP ? $\endgroup$
    – Sofiane
    Oct 23, 2016 at 11:45
  • $\begingroup$ Could you please answer the last comment ? Then your answer will be the accepted one. $\endgroup$
    – Sofiane
    Oct 25, 2016 at 10:55
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    $\begingroup$ 'around' means 'in the vicinity'. The electron moves, near the nucleus. We can't define its trajectory because of the Uncertainty Principle: its position cannot be determined with arbitrary precision. No precise position vector means no well-defined orbits. We call the spatial area where the electron is most likely to be found an orbital. Thanks. $\endgroup$
    – Gert
    Oct 25, 2016 at 12:04

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