In 1908, Ernest Rutherford conducted his greatest experiment.
First, he directed alpha particles at several different materials and found that they passed through easily.
Rutherford beat a piece of gold leaf into a thinness of one fifty-thousandth of an inch. He estimated that the gold leaf was now about 2,000 atoms thick.
If atoms filled that space and the atom was indestructible, then the particles would not get through. Again, almost all the particles went through easily, a small number of them were slightly deflected by something, and an even smaller number bounced backward.
Rutherford knew that there was only one conclusion: most of the atom must be empty space that allowed the particles to pass through.
He said the positive alpha particles acted just as if they had been repelled by another small, powerful positive charge, a charge concentrated at one point.
Rutherford’s model of the atom started at the center with a tiny, positively charged nucleus (from the Latin for “kernel”) containing most of the mass of the atom. Since an atom has a neutral charge, he had to also account for a negative charge somewhere in the atom.
He returned to Thomson’s electrons, but he knew they were not scattered throughout the atom. He reasoned that the electrons were negatively charged, giving the atom a neutral charge.
To account for the vast amount of empty space within the atom, he concluded that the electrons must be a very great distance from the nucleus. He compared it to our solar system with the planets being electrons and the Sun being the nucleus.
There were still some details to be worked out, but Rutherford’s model was correct.
Scientists were now inside the atom.