Then one day, a strange thing happened. The Curies were busy refining uranium from its ore, pitchblende. But they suddenly noticed that the ore seemed to be more radioactive than the uranium itself! How could this be? The only explanation, Madame Curie thought, was that there must be another, stronger, radioactive element in pitchblende.
In 1898, after working through tons of pitchblende, the Curies succeeded in separating a speck of a new element that was 900 times more radioactive than uranium! They named the new element radium.
The Curies and other scientists were very excited. Here were three elements—uranium, thorium, and radium—all giving off powerful rays. Where did the rays come from? Scientists were sure they could only come from the atoms of the elements themselves. But how could that be? There couldn't be anything smaller than an atom. Or could there? The scientists didn't know. It was a real mystery.
4
WHAT'S IN AN ATOM?
Every mystery is sure to attract some people who wish to solve it. And the mystery of radioactivity was no exception. Scientists in many parts of the world began to search for clues. Little by little, they found them. It wasn't until the 1930's that the last pieces of the puzzle began to fall into place—the structure of the atom was finally clear.
But before we talk about the structure of atoms, let's talk about the structure of houses. Many houses are built of wood, shingles, and glass. However, even though the houses are built of the same materials, they may not look anything alike. Some are ranch houses, some are split levels, and some are colonial houses.
On the other hand, sometimes a builder puts up a large development in which all the houses are exactly the same. If a new friend tells you that he lives in the Shady Acres development, you can picture his house. It is just like every other house in Shady Acres.
Are you wondering what this has to do with atoms? Well, all atoms are built of the same principal materials.
They are called protons, electrons, and neutrons. And just as a ranch house never looks exactly like a colonial house, an atom of one element never looks exactly like the atom of another element.