History of the Atom and Periodic Table
Around 400 B. C., Democritus claimed all matter was made of tiny, indivisible particles called “atoms”. Aristotle disagreed and claimed matter was made of earth, wind, water, and fire. Democritus and Aristotle
Mendeleev was responsible for creating the 1 st periodic table. Elements were arranged by atomic mass. Dmitri Mendeleev
Henry Moseley created the Modern Periodic Table of Elements that we use today. It is arranged by atomic number rather than mass. Henry Moseley
In the early 1800s, Dalton created his atomic theory about matter. John Dalton
Thomson discovered the first subatomic particle called the electron. Electrons are negatively charged and orbit the nucleus. He later discovered a subatomic, positively charged particle in the nucleus called the proton. J. J. Thomson
Rutherford realized that atoms had a nucleus in the center that is orbited by electrons. Between the two is a lot of empty space. Ernest Rutherford
Bohr expanding on the atomic model by placing electrons on separate energy levels. Niels Bohr
Chadwick discovered the last subatomic particle that had a neutral charge and it is called the neutron. His discovery made us realize isotopes existed. Isotopes are atoms of the same element with a different number of neutrons. Proved Dalton’s Atomic theory was incorrect again by showing atoms of the same element can be different. James Chadwick