ABSTRACT
At the largest scales in the universe the force between bodies is due to gravity. No other forces operate at great distances. This is because all other forces are both attractive and repulsive, and the effects cancel each other out when the objects are far apart. At the atomic scale, gravity still operates, but only very weakly. Just how weakly becomes apparent when we consider that the repulsive force between two electrons is 1042 times greater than the attraction due to gravity. Even stronger forces exist within the nucleus, but these have no bearing on the forces between atoms: just as with electrical forces between planets, the various positive and negative nuclear forces are cancelled out before reaching the edges of the atom. Thus, electrical forces are all we need to consider if we wish to understand the chemical behaviour of atoms.
