Atoms react because they wish to become a Noble Gas, and they do this by sharing, gaining, or losing electrons to become stable. The correct answer therefore is, "do so to share, gain, or lose electrons to become stable". Not all atoms have a full octet of electrons in their valence shell, this is dependent based on what type and how it's obtained. They can't be separated again through "physical" means and the claim "all atoms lose electrons" is invalid.
