Atomic Timeline by Jason Gwozdz

Democritus

460

He asked if matter could be divided into smaller and smaller peices forever, or if their was a limit to the amount of times a peice of matter could be divided. His theory was matter could not be divided into smaller and smaller pieces forever, eventually the smallest possible piece would be obtained. This piece would be indivisible. He named the smallest piece of matter “atomos,” meaning “not to be cut.”

Joseph Proust

Dec 7, 1774

Proust published the Law of definite proportions. This law states that a compound is composed of exact proportions of elements by mass regardless of how the compound was created.

Antoine Lavoisier

Dec 7, 1783

Antoine created the Law of conservation of mass. The law states that matter cannot be made or destroyed. He also hints at the rearrangement of matter in reactions. Matter rearranged, but never disappeared.

John Dalton

Oct 30, 1803

He based his theory off of experimental observations. 1.All matter is made of atoms. Atoms are indivisible and indestructible. 2.All atoms of a given element are identical in mass and properties. 3.Compounds are formed by a combination of two or more different kinds of atoms. 4.A chemical reaction is a rearrangement of atoms. 5.Atoms can be neither created nor destroyed.

J.J. Thomson

Oct 29, 1897

Thomson discovered the neutron and proton which changed the look of an atom from a billard ball to a sphere that had smaller balls embedded in it. He called this the plum pudding model. He infered that an atom is a sphere made up of positively charged protons with negatively charged electrons embedded in it. To find this J.J.Thomson used a highly evacuated discharge tube.

Albert Einstein

Dec 7, 1903

Einstein theorized that atoms may exist but also had a way to prove it. He did this by using his theories in quantum physics to explain the photoelectric effect and Brownian motion, which ultimately led to solid evidence that atoms exist and even showed how atoms are structured.

Ernest Rutherford

Mar 7, 1909

Ernest discovered the atomic nucleus and proved J.J. Thomson's plum pudding model wrong. To do this he used his famous gold foil experiment which was preformed by Hans Geiger and Ernest Marsden in 1909. Rutherford's experiment consisted of a beam of alpha particles, generated by the radioactive decay of radium, directed normally onto a sheet of very thin gold foil in an evacuated chamber.

Niels Bohr

Oct 31, 1913

Niels Bohr refined Rutherfords model of the atom by assuming that electrons travel in stationary orbits defined by their angular momentum. This led to the calculation of energy levels of possible orbits. When jumping from one orbit to another with lower energy, a light quantum is emitted.

Louis de Broglie

Dec 7, 1924

Louis suggested that electrons could act like both particles and waves. His hypothesis was soon confirmed in experiments that showed electron beams could be diffracted or bent as they passed through a slit much like light could.

Erwin Schrödinger

Dec 7, 1926

In 1926 Erwin derived a set of equations or wave functions for electrons. According to Schrodinger, electrons confined in their orbits would set up standing waves and you could describe only the probability of where an electron could be. The distributions of these probabilities formed regions of space about the nucleus were called orbitals. Orbitals could be described as electron density clouds.

Werener Heisenburg

Dec 7, 1927

Heisenburg was responsible for the uncertainty principle. "The more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa." Heisenburg 1927.

James Chadwick

Oct 31, 1932

Chadwick made a fundamental discovery in nucleur scinece. Hed discovered the neutron. He also discovered that the atomic number is discovered by the number of protons.