Tin added in small amounts to copper makes bronze. This results in bronze which is much stronger than both copper or tin. In pure metals, the atoms are arranged in orderly rows and columns. Each atom gives up some of its electrons to create a kind of sea of these randomly moving charged particles. This sea of electrons makes for flexible, metallic bonds that slide past each other, like in copper. This means the material is soft, and easy to dent, which is not ideal for a bell 's ring. A stiffer material is required, so tin is added. These large tin atoms restrict the movement of the copper atoms, making the overall structure stiffer, making a better bell with a high sound quality.