Atomic Theory Timeline

Democritis

400 BCE

He had the idea of small, indestructable things that he called atamos. Atamos means invisable. He said that these are the building blocks of life but no one beleived him because of other influetial scientists during his time.

Lavoisier

1783

He was an important French chemist and leading figure in the 18th-century chemical revolution, he developed a theory of the chemical reactivity of oxygen and also drafted the modern system for naming chemicals. He also made the idea of compounds.

John Dalton

1803

John Dalton’s strongest work in chemistry was his atomic theory. He based his theory of partial pressures on the idea that only similar atoms in a mixture of gasses bounce off one another, but unlike atoms appear to react complacent toward each other.

Dmitri Mendeleev

1869

Mendeleev taugh chemistry though, he couldn't find a textbook that met his needs. Since he had already published a textbook on organic chemistry that had been awarded the Demidov Prize, he was going to write another one. When he began to make the chapter on the halogen elements at the end of the first volume, he compared the properties of his group of elements to the group of alkali metals. so he made the periodic table.

Thomason

1897

In 1897 he showed that cathode rays are rapidly moving particles, and, by measuring their displacement by electric and magnetic fields, he determined that these particles were nearly 2,000 times less massive than the lightest known atomic particle. Originally called corpuscles by Thomson, the particles are now known as electrons.

Ernest Rutherford

1911

Thomson studied the charge-to-mass ratio of the most common ion, which now is called the electron. Rutherford looked at ultraviolet radiation first and then at radiation emitted by uranium. Placement of uranium near foil showed Rutherford that the radiation was more complex than what he previously thought: one type was easily absorbed or blocked by a thin foil, but another type often broke through the same foils.

Bohr

1913

Neils Bohr was a danish physicist who studied atoms and found out more about the nucleus and had a model. His model was the first that had quantum theory. The Bohr model and all of the ones to come describe the properties of electrons in terms of a set of possible values. It shows that atoms absorb or give off radiation only when the electrons jump between states.

H.G.J Moseley

1914

Moseley’s law is an extremely important discovery concerning atomic numbers. In 1914 Moseley published a paper where he concluded that the atomic number is the number of positive charges in the nucleus. He also stated that there were three unknown elements, with atomic numbers 43, 61, and 75, between aluminum and gold. Those were Technetium (43), Illinium (61), and Rhenium (75)

Heisenberg

1925

In 1925, after an extended visit to Bohr’s Institute of Theoretical Physics at the University of Copenhagen, Heisenberg tackled the problem of spectrum intensities of the electron taken as an anharmonic oscillator. In an exchange with Dirac, Jordan, Wolfgang Pauli, and others, he embarked on a research program to create a quantum field theory, uniting quantum mechanics with relativity theory to comprehend the interaction of particles.

James Chadwick

1932

Chadwick went to England to study under Rutherford at the University of Cambridge. There he and Rutherford studied the transmutation of elements. Chadwick was convinced that alpha particles did not have enough energy to produce such powerful gamma-rays. He performed the beryllium bombardment experiments himself and interpreted that radiation as being composed of particles of mass approximately equal to that of the proton but without electrical charge—neutrons.