Response of a rare-gas atom in a uniform electric field An atom of a rare gas is placed in a uniform electric field E. What happens to the nucleus, and how does this relate to atomic polarization?

Introduction / Context:Atomic polarization in rare gases (closed-shell atoms) under a uniform electric field is purely electronic: no permanent dipoles exist, and polarization is induced by a slight distortion of the electron cloud relative to the nucleus.

Given Data / Assumptions:

• Uniform external electric field E (no field gradient).
• Closed-shell, spherically symmetric rare-gas atom.
• Linear response regime (small distortions).

Concept / Approach:In a uniform field, the center of mass of the atom experiences no net acceleration internally; polarization manifests as a tiny relative displacement between the electron cloud and the nucleus. The electron cloud shifts slightly opposite to E (negative charge), creating an induced dipole p aligned with E. The nucleus, being massive and strongly bound at the atomic center, is commonly treated as stationary in the atomic frame.

Step-by-Step Solution:Induced dipole relation: p = αE, where α is electronic polarizability.Microscopically, electrons displace by a small amount δ opposite to E; nucleus remains effectively fixed in the atomic frame.Resulting separation produces the dipole moment with no need to invoke nuclear displacement.

Verification / Alternative check:Classical “spring” models of bound electrons (Lorentz oscillator) produce the same conclusion: restoring force holds the nucleus fixed while the electron cloud distorts slightly, yielding polarization proportional to E.

Why Other Options Are Wrong:Statements asserting nucleus translation misunderstand the internal relative motion; in a uniform field, the dominant effect is electron displacement. “Independent of E” contradicts linear polarizability, and “nucleus leaves the atom” is unphysical at ordinary fields.

Common Pitfalls:

• Confusing the relative displacement within the atom with rigid-body translation.
• Forgetting charge signs: electrons shift opposite to E while the induced dipole aligns with E.

Final Answer:The nucleus will not be shifted (polarization arises from electron-cloud displacement)