Atomic timeline

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Atomic timeline

Atomic Timeline

By: Emily,Ellie, and Riley



1869-Dmitri Mendeleev1834-1907

John Dalton transformed Democritus's ideas into a scientific theory known as the Atomic Theory. The atomic theory stated that all elements are composed of atoms, atoms of the same element are identical, atoms of different element can physically mix together or chemically combine to form compounds, and chemical reactions occur when atoms are separated, joined or rearranged.

1803- John Dalton1760-1844

1909-Robert Millikan1868-1953

Robert Millikan determined the unit charge of an electron using his oil drop experiment. He then figured out that the electron carries one unit of negative charge and 1/1840 the mass of a proton.

1932- James Chadwick1891-1974

1926-Erwin Shrodinger1887-1961

James Chadwick discovered the uncharged partical called the neutron. He also reasoned that neutrons were important to holding together protons

Erwin Shrodinger developed a mathematical equation to describe the motion of electrons in atoms. He viewed electrons as continuous clouds, which led to the electron cloud model

Dmitri Mendeleev created one of the first models of the periodic table.He arranged the table in order of increasing atomic mass.His model was arranged in 7 groups based on repeating properties. Mendeleev also left holes in the table for elements that were yet to be discovered

1913-Henry Moseley1887-1915

Henry Moseley discovered that the energy of x-rays emitted by the elements increased in linear fisionwith each successiveelement in the periodic table. He then reasoned that this relationship was a function of the positive charge on the nucleus. Moseley then rearranged the periodic table by increasing atominc number like we use today.

1904- J.J. Thomson1856-1940

1926- Elctron Cloud Model

Democritus was a Greek philosopher who discovered the atom and proposed it was indivisible and indestructable. However, his ideas did not explain chemical behavior and lacked expiremental support.

460 BC- Discovery of the Atom

1789- Law of Conservation of Mass

Antoine Lavoiser determined the composition of many compounds, and in 1789, formulated the Law of Conservation of Mass. This states that during a chemical reaction, mass is neither created nor destroyed.

Ernest Rutherford decided to test the current theory of atomic structure. To do this, he set up what is known as the Goldfoil Expirement, in which alpha particles were fired at a very thin sheet of goild foil. The results of this were not as he expected, and this led to the Rutherford model, which protrays the nucleus of an atom as very small and dense, and with a posative charge, and shows the electrons outside the nucleus.

1911-Ernest Rutherford1871-1937

Niels Bohr went on to discover the quantum mechanical model which determines the energy allowed for an elctron and how likely it is to find the electron in many locations around the nucleus. He also introduced the Bohr planetary model that presonts the atom as a small, positevely charged nucleus surrounded by elctrons that travel in a circular form around the nucleus

1933- Niels Bohr 1885-1962

J.J. Thomson discovered the elctron. He also had discoved the plum pudding atomic model which stated that atoms were uniform spheres of positively charged matter and electrons were embedded.

The elctron cloud model displayed the locations of electrons in an atom. Many scientists had worked on the development of the cloud including, Ernest Rutherford, Niels Bohr, and Werner Heisenberg.

1897- Cathode Ray tube

The Cathode Ray tube was a vaccuum tube that produces images when its phosphorescent surface is hit by electron beams. This tube was discovered by a German physicist Ferdinand Braun.

Rutherford's Model

Ernest Rutherford



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