I've just started a course on organic chemistry and the professor said some things which did'nt exactly make sense to me: 1) In a period, atoms are more electronegative as we go to the right. The more electronegative an atom is, the more stable it becomes. 2) In a group, atoms increase in size as we go downwards. The greater an atom's size, the more stable it is. Now I know the periodic trends but what I don't get is how an atom is more stable if it is more electronegative? Here's what I think (feel free to point out any mistakes). By stability we mean an atom's inertness or the tendency of a certain atom to not react. For example suppose S is more reactive then Q, so we could say that Q is more stable than S. But how does an increase in electronegativity increase stability. The way I see it, if a certain atom is more electronegative it should attract a neighbouring atom with more force and thus be more reactive and less stable.