Nature of the force between atoms and molecules
Newton’s law of universal gravitation which works so well in calculations of the force between two pieces of matter whose distance apart is large compared with the size, fails to give the right answer when applied to two molecules. close together. This does not mean that gravitational attraction no longer acts but t incomparably greater forces of a different kind come into action. Now a full acco of these forces belongs to very advanced physics, so we shall deal with the subj very briefly.
Later on we shall learn about electricity and see that it can produce electric – magnetic forces of attraction and repulsion. Atoms themselves contain particles electricity in motion and so we get electric and magnetic forces between them. shall, therefore, sum up the situation by saying that, when atoms are very c together, the forces between them are electromagnetic in nature. The net result is that, when their centres are a certain distance apart, resultant force between two atoms or molecules is zero. When closer than this .- repel one another and when further apart they attract one another. Furthermore these electromagnetic forces differ from one kind of atom to another and between atoms of the same kind depending on whether a substance is in the close state or some particular kind of solid state. A good example of a substance can exist in more than one kind of solid state is carbon.