Explain the electron displacement effects in covalent bonds.

(N/A) The electron displacement in an organic molecule may take place either in the ground state under the influence of an atom or a substituent group or in the presence of an appropriate attacking reagent.
$(i)$ The electron displacements due to the influence of an atom or a substituent group present in the molecule cause permanent polarisation of the bond. Inductive effect and resonance effects are examples of this type of electron displacement.
$(ii)$ Temporary electron displacement effects are seen in a molecule when a reagent approaches to attack it. This type of electron displacement is called the electromeric effect or polarisability effect.