We know that atoms are held together by atomic bonds and when one atom is moved away from the one it's bonded to, there is a restorative force that 'pulls' it back. But how can we explain the nature of this force in terms of the electrostatic/electromagnetic forces between charged atomic particles (proton & electron)? In a covalent bond an electron is shared between two atoms (i.e. its wavefunction is spread over a wider area), but how does that explain the restorative force? If I move one atom away from another, I'm moving the positively charged nucleus away from this shared electron, so the electrostatic force between the nucleus and the electron should only get smaller, not larger (as hooke's law predicts).