History of the Atom

Democritus

200

Democritus lived in Greece around 500 BC. He had believed that all matter consisited of smaller paticles. Also, he believed they couldn't be divided. Thus, he named these particles atoms. This came from the Greek word atomos, which meas "uncut". Democritus also thought that there were different types of atoms.

Aristotle

200

Aristotle also lived in Greece around 200 BC. He believed that there wasn't a limit on how many times matter could be divided.

Antoine Lavoisier

Oct 6, 1789

The "father of modern chemistry", he was a French nobleman in the histories of chemistry and biology. He stated the first version of the law of conservation of mass, recognized and named oxygen, and hydrogen. He abolished the phlogiston theory and helped construct the metric system, He wrote the first extensive list of elements, and helped to reform chemical nomenclature. He discovered that, although matter may change its form or shape, its mass always remains the same.

John Dalton

Sep 3, 1803

Dalton was a teacher who spent a lot of his free time doing scientific experiments. He was very interested in predicting weather. This lead him to eventually study the behavior of gases in air. So, based on the way gases exert pressure, Dalton concluded that a gas consists of indivual particles (atoms). Dalton came up with this idea by measuring the masses of element that combine when compounds form. Also, he founded that no matter how big or small the samples, the ratio is always the same.

J.J. Thompson

Apr 30, 1897

Thompson used an electron current to study more about atoms. He did this by using a device he created to make a positive and negative charge.

Hantaro Nagaoka

Oct 31, 1904

Nagaoka suggested that an atom has a central nucleus. Also, he found that electrons move in orbits like the rings around Saturn.

Robert Milikan

Feb 11, 1909

He was an American experimental physicist, and Nobel laureate in physics for his measurement of the charge on the electron and for his work on the photoelectric effect. in 1909 Millikan worked on an oil-drop experiment in which they measured the charge on a single electron. His experiment measured the force on tiny charged droplets of oil suspended against gravity between two metal electrodes.

Ernest Marsden

Nov 1, 1909

Marsden made a major contribution to Ernest Rutherford's gold foil experiment.

Ernest Rutherford

Oct 28, 1911

Rutherford discovered that uranium emits fast-moving particles that have a positive charge. Ernest called them alpha articles. In 1909, he asked a student, Ernest Mardsen, to find out what happens to alpha particles when they go through a sheet of gold. Based on Thomson's model, Rutherford hypothesized that the mass and charge at any location in the gold would nbe to small to change the path of an alpha particle.

Niels Bohr

Oct 31, 1913

Bohr agreed that atoms have a central nucleus and that its surrounded by a large volume of space. But his model had one special difference, it focused on electrons. Niels described the placement of electrons in great detail. His model is similar to the planets around the sun.

Louis de Broglie

Oct 31, 1924

Proposed that moving particles like electrons have some properties of waves. A few years later, evidence was collected to support this idea.

Erwin Schrodinger

Apr 28, 1926

Schrodinger developed a mathematical equations to desribe the motion of electrons in atoms. His work leads to the electrons cloud model.

James Chadwick

Oct 20, 1932

Chadwick confirmed that the exsistence of neutrons, which have no charge. Atomic nuclei contain neutrons and positively charged protons.