Rutherford’s Gold-Foil Experiment

Radioactivity

Radioactivity had been discovered recently, in 1895, by Henri Becquerel, based on Wilhelm Roentgen’s “photograph” of his wife’s hand’s bones.

Becquerel had put uranium crystals into a drawer with photographic plates, and they had ended up “fogged.”

Further Research

Marie and Pierre Curie isolated polonium and radium.

They realized that some elements emitted energy, and some emitted particles.

Rutherford and Radioactivity

Ernest Rutherford used alpha particles to investigate the gold atom in 1908.

He conducted a famous experiment that proved that atoms are not solid spheres as proposed by Dalton, or “plum-puddings,” as Thompson said.

The Alpha Particles Experiment

In his experiment Rutherford used a very thin sheet of gold as a target, and he shot a beam of alpha particles at the gold.

– alpha particles (-particles) are helium nuclei without electrons, and are a form of radioactivity

Nearly all of the alpha particles passed through the thin sheet of gold.

Rutherford also noticed that a few particles were deflected from their straight- line path, some by 90 degrees or more.

Conclusion The beams were bouncing off the

positively charged core of the atoms. Rutherford originally called this a proton,

because it was positively charged. Later, it was renamed the nucleus. The

nucleus of the atom has almost all the mass of the atom.

Therefore, most of an atom is empty space.