Timeline of the atom

Democritus

460

http://en.wikipedia.org/wiki/DemocritusDate: 460-370 BC
Location:Greece
Idea/experiment: Taken from Leucippus, he formulated a theory on the understanding of atomic structure similar to modern science.
How this contributed to our understanding of the atom: Democritus stated that everything was composed of atoms which differ in shape and size. Atoms are indestructible and lie between an empty space. He also stated that the solidness of the material corresponded to the shape of the atoms involved.

timeline of the atom

Period: 460 to Jan 1, 1932

Isaac Newtown

Jan 1, 1704

http://en.wikipedia.org/wiki/Isaac_NewtonDate: 1704
Location: England
Idea/experiment:Isaac Newtown formulated a theory of light and described the universal gravitation and the three laws of motion.
How this contributed to our understanding of the atom: He suggested that atoms are held by attractions, which is known as forces and stated that ‘matter is formed of solid, massy, impenetrable particles.’ he also suggested that atoms in a gas were more or less static.

John Dalton

Jan 1, 1803

http://en.wikipedia.org/wiki/John_Dalton Date:1803
Location: England
Idea/experiment: The development of the modern atomic theory

How this contributed to our understanding of the atom: His contribution to atomic theory was that he stated that (1) all matter was composed of small indivisible particles termed atoms, (2) atoms of a given element possess unique characteristics and weight, and (3) three types of atoms exist: simple (elements), compound (simple molecules), and complex (complex molecules).

G.J. Stoney

Jan 1, 1894

http://en.wikipedia.org/wiki/G._J._Stoney Date: 1894
Location: Ireland
Idea/experiment:G.J. Stoney theorized that electricity was comprised of negative particles he called electrons (fundamental unit quantity of electricity.)
How this contributed to our understanding of the atom: His contributions to research in this area laid the foundations for the eventual discovery of the particle by J.J. Thomson in 1897.

J.J.Thomson

Jan 1, 1897

http://en.wikipedia.org/wiki/J.J._ThomsonDate: 1897
Location: Britain
Idea/experiment:He discovered the electron and of isotopes and the invention of the mass spectrometer.
How this contributed to our understanding of the atom:The Nernst-Thomson rule stated that it is difficult for charged ions to attract each other through insulating water so they dissociate.

Max Planck

Jan 1, 1900

http://en.wikipedia.org/wiki/Planck , Date: 1900
Location: Germany
Idea/experiment:Max Planck proposed the idea of quantization to explain how a hot, glowing object emitted light
How this contributed to our understanding of the atom: Planck contributed to be the founder of the quantum theory and thus one of the most important physicists and also considerably to extend the special theory of relativity.

Hantaro Nagaoka

Jan 1, 1903

http://en.wikipedia.org/wiki/Hantaro_Nagaoka Date: 1903
Location: Japan
Idea/experiment:Hantaro Nagaoka proposed an atomic model called the Saturnian Model to describe the structure of an atom.
How this contributed to our understanding of the atom:Nagaoka made an incorrect planetary model of an atom which was based on the analogy about the stability of the Saturn rings. The model made two predictions: a very massive nucleus and electrons revolving around the nucleus bound by electrostatic forces.

Robert Andrews Millikan

Jan 1, 1909

http://en.wikipedia.org/wiki/Robert_Andrews_MillikanDate: 1909
Location: America
Idea/experiment:Millikan worked on an oil-drop experiment in which they measured the charge on a single electron.
How this contributed to our understanding of the atom:The elementary charge is one of the fundamental physical constants is great importance if the accurate value is known. He measured the force on droplets of oilbetween two metal electrodes. Knowing the electric field, the charge on the droplet could be determined.

E. Rutherford

Jan 1, 1911

http://en.wikipedia.org/wiki/Ernest_RutherfordDate:1911
Location:British/New Zealand
Idea/experiment:Became known as the father of nuclear physics he continued Hantaro Nagaoka’s work by making the Rutherford model and used the gold-foil experiment.
How this contributed to our understanding of the atom:Rutherford model showed that atoms have their positive charge concentrated in a very small nucleus. His model shows that electrons orbited the nucleus.

H.G.J.Moseley

Jan 1, 1914

http://en.wikipedia.org/wiki/Henry_MoseleyDate: 1914
Location: England
Idea/experiment:Discovered that the number of protons in an element determines its atomic number.
How this contributed to our understanding of the atom:Moseley’s contribution was the justification of physical laws of the chemical and empirical concept of the atomic number. this was from the development of Moseley’s law in X-ray spectra.

Neils Bohr

Jan 1, 1922

http://en.wikipedia.org/wiki/Niels_Bohr Date:1922
Location: Denmark
Idea/experiment:Proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit.
How this contributed to our understanding of the atom: He made contribution to understanding atomic structure and quantum mechanics.

James Chadwick

Jan 1, 1932

http://en.wikipedia.org/wiki/James_ChadwickDate: 1932
Location:England
Idea/experiment: He used alpha particles and discovered a neutral atomic particle with a mass close to a proton. He discovered the neutron.
How this contributed to our understanding of the atom: Chadwick's discovery was crucial for the fission of uranium 235. Neutrons do not need to overcome any Coulomb barrier and can therefore penetrate and split the nuclei of even the heaviest elements.