Today, we are going to review the Historical Development of Atomic Theory. Can you share what you remember?
In 1803, John Dalton created the atomic theory and stated that elements are made of tiny particles called atoms, and atoms can’t be created or destroyed through chemical process.
In 400 B.C., Democritus stated that everything is made out of atoms. He made an atomic model with no protons, no neutrons, and no electrons.
Great! What about Goldstein and Thomson?
In 1897, J. J. Thomson concluded that all atoms have negative charge, and it was named electron.
In 1885, Goldstein discovered positive particles by using a tube filled with hydrogen gas. The particle was named proton.
That's good that everyone know about the historical development of atomic theory and the people behind it.
In 1932, James Chadwick discovered neutron by putting a piece of beryllium in a vacuum chamber with some polonium. The polonium emitted alpha rays, which struck the beryllium. The beryllium emitted the neutral rays.
In addition to that, in 1914, Henry Moseley attempts to determine the number of protons in the nucleus of each atom. However, he was unsuccessful to determine it because the neutron had not been discovered yet.
That's all! Thank you so much for participating the class. I hope you will remember those important details.