Why does a rubber band's tension grow when stretched?

[sillycow]

My very beginner level understanding is that the rubber band's tension stems from it's particles being held together by it's electric bonds: Atoms and molecules are bound together by their electric charges.

And so, When I stretch a rubber band, I am presumably pulling it's particles away from each other: Same amount of atoms/molecules are distributed over a longer space. The electric force diminishes as charges are pulled further apart from each other, so I would expect the tension to also shrink.

Then why does tension grow when the rubber band is stretched?

 

[Chestermiller]

Rubber is made up of very long chains of polymer molecules that are attached to each other at various locations called "cross links." In between the cross links, the polymer chains are not straight. They are very bunched up, and much shorter than their extended length. The segments of the chains have kinetic energy which keeps them bunched up. When you extend the rubber, what you are doing is stretching the chains (moving their cross link points apart), and, because of the kinetic energy of the segments, the chains act like little springs. This is what causes the tension when you stretch the rubber.