Discovery of Atoms

The atom was pictured in many different ways until its true properties were illustrated in modern physics. The quest for understanding the composition of matter led to such a discovery and continues to yield new discoveries about how atoms are structured and what they are made of.

First Encounter

In the early years of the 1800s, John Dalton started studying what matter was composed of. He shortly discovered that matter comprises of very tiny units called atoms when he noticed that hydrogen always mixes with oxygen at the same proportion (two atoms of hydrogen to one atom of oxygen).

Discovery of Electrons

In 1897, Joseph Thompson studied the flow of electricity through very light gases and noticed that current flows through positive and negative subatomic particles. His studies led to the discovery of an ultra-light subatomic particle called an electron.

Atoms Have Compact Nuclei

In 1911, Ernest Rutherford noticed that alpha particles traveling through atoms were heavily dispersed. The only way to explain this was to state that an atom is comprised of a very small and concentrated nucleus with electrons orbiting it.

Neutrons

There was much confusion about the properties of helium atoms, since their atomic weight was four times as much as hydrogen atoms, but they only had twice the positive charge. In 1932, James Chadwick came up with the conclusion that there were particles with no charge inside atoms, called neutrons.

Quarks

It was discovered in 1964 that subatomic particles in atoms contain smaller particles known as quarks, which give subatomic particles their bulk and characteristics.

References

• The Discovery of Atoms and Nuclei
• Quark Definition