Atomic Theory

Democritius

442

Democritus was the man who discovered the atom. This happened around the middle of his lifetime.If it weren't for him we would know nothing about atoms and if we did we wouldn't be nearly as far. He found it with a seashell but he believed that atoms were indestructible.The experiment that Democritus used was he took a shell and broke it into smaller and smaller pieces until he could break it no more. And this how he discovered the atom.

John Dalton

Sep 23, 1803

Dalton made the first useful theory of matter in 1803 A.D. He was a meteorologist who find out about water evaporating into the air and he concluded that they must be combining in the air. He developed that the sizes of particles of different things must be different. Proposed atomic theory with spherical solid masses in motion. He performed an experiment on mixtures of gasses what effect the properties of individual gases had on the properties of a mixture as a whole.

J.J. Thompson

Sep 23, 1889

Found that there were smaller particles than an atom which turned out to be called electrons. If a gas sample is introduced into the region between two charged plates, a current flow can be observed, suggesting that the atoms have been broken down into charged constituents. The source of these charged particles is a heated cathode that, in fact, causes the atoms of the sample to ionize. These were known as cathode rays.

Robert Miliken

Sep 23, 1908

He found about how when the atoms are charged that he will be able to suspend the particles in air.He sprayed a small fine mist of oil droplets into a chamber. Some of the droplets fell through a hole in the upper container. Milkan let them fall until they reached terminal velocity due to air resistance. Using a microscope he measured the velocity and calculated the mass of each oil drop.Then he applied a charge to the oil droplets.He then used a battery to suspend the drops in air.

Ernest Rutherford

Sep 23, 1909

Rutherford (known as the father of nuclear physics) developed the theory for the structure of an atom. He used a gold foil experiment, observing the scattering of alpha particles, and demonstrated for the first time the existence of the atomic nucleus.

Niels Bohr

Sep 23, 1913

Neils Bohr developed the Bohr atomic model, with electrons travelling in orbits around the nucleus, and chemical properties being determined by how many electrons are in the outer orbits. He also integrated the Planck quantum theory, stating that when electrons change orbits they emit a quantum of discrete energy.
He is the creator of the bohr model.

James Chadwick

Sep 23, 1931

James chadwick is the man who discovered the neutron. He gave way for things heavier than uranium.In 1932, English Physicist James Chadwick, after a decade-long struggle to track down this tricky particle (all the methods available at the time were used only to detect charged particles), performed tests on a new type of radiation which had been frustrating physicists for years, and which had previously been mistaken for gamma rays.