They are in discrete energy levels, but don't forget that these are further divided into orbitals. Also the more electronegative atom pulls the bonding pair of electrons closer to it, and these electrons are always on the outer shell.
So no it wouldn't change the 'molecular structure', just the probability that an electron can be found closer to the more electronegative atom in a bond.
(Original post by s.aley)
I know that the more electronegative atom will become slightly negative, but how does that occur?
I was under the impression that electrons only exist in discrete energy levels, if the more electronegative atom 'pulls the electrons closer' then wouldn't that change the discrete energy level the electron is in and hence change the molecular structure?
Electrons should not be considered as being a single particle. When considering bond polarity the electron-cloud model is used. According to quantum mechanics, the energy levels of the electron is the level where the probability of finding the electron is greatest. Electrons however are constantly on the move and forms charge clouds in their orbitals.
A more electronegative element can attract this electron so that it spends more time closer to it. Thus the charge cloud gets distorted and looses its symmetry. This causes a partial negative and positive charge to form and hence causes bond polarity.
And of course there is a change in energy level. Think of it this way: When the electron is exited and leaves the atom, it becomes an ion with a positive charge. This causes a change in energy level from outer shell to out of the atom. However, here the electron does not leave the atom, just goes further away from it, and hence there is only a partial charge.