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340
Aristotole
Aristotle didnt think atoms could be constantly moving. He believed there were four elements only, water, fire, air and earth and that they would align into their rightful place and be at rest. -
400
Democritus
The Idea of the atom were first proposed by the Greek philosophers Democritus and Leucippus around 400 B.C. At the time there was no real evidence to support the proposal. The atom was suggested to be what all matter is made of. -
Period: 400 to
Development Of The Periodic Table Timeline
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Hennig Brand
Discovered Phosporus -
Robert Boyle
He measured relationships between volume and pressure of gases. From his experiments he concluded that gases are made up of tiny particles that group together to make different substances -
Issac Newton
In 1704, Sir Isaac Newton, an English physicist and mathematician proposed a mechanical universe with small, solid masses in motion. -
Antoine Lavoisier
Antoine created the idea of having a single language for all of science to use. For example when someone called a substance hydrogen, than everyone was to call it hydrogen. This allowed for science to advance and for chemists to learn new properties of other metals and know how to organise them without getting confused of different names from different languages -
John Dalton
John Dalton was an English chemist, meteorologist and physicist. In 1803, John Dalton Proposed an "atomic theory".
Five main points of Dalton's atomic theory:
Elements are made of extremely small particles called atoms.
Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
Atoms cannot be subdivided, created, or destroyed.
Atoms of different elements combine in simple whole-number ratios to form chemica -
Johann Dobereiner
Johann Dobereiner noticed that the atomic weight of strontium fell midway between the weights of calcium and barium which were elements possessing similar properties, In 1829, after discovering the halogen triad composed of chlorine, bromine, and iodine and the alkali metal triad of lithium, sodium and potassium he proposed that the middle element had to be an average of the other two elements this was called the Law of Triads -
Jakob Berzelius
Jakob Berzelius developed a table of atomic weights & introduced letters to symbolize elements -
Michael Faraday
In 1832, Michael Faraday reported that the quantity of elements separated by passing an electric current through a molten or dissolved salt is proportional to the quantity of electric charge passed through the circuit. This became the basis of the first law of electrolysis:
m = k . q Second law of electrolysis Faraday discovered that when the same amount of electricity is passed through different electrolytes, the mass of substance liberated/deposited at the electrodes is directly proportional -
J.Plucker
In 1859, J. Plucker found that the electric discharge caused a fluorescent glow to form on the glass walls of the vacuum tube (cathode ray tube). It was later shown that the glow was produced by cathode rays. -
Alexandre-Emile Béguyer de Chancourtois
French geologist who arranged the elements in order of increasing atomic weights. He plotted the elements on a cylinder, which he called the telluric helix. Alexandre-Emile Béguyer de Chancourtois listed the elements on paper tape and wound them, spiral like, around a cylinder. Certain ‘threes’ of elements with similar properties came together down the cylinder. -
John Newlands
John having arranged the 62 known elements in order of increasing atomic weights, noted that after interval of eight elements similar physical/chemical properties reappeared. Newlands was the first to formulate the concept of periodicity in the properties of the chemical elements. In 1863 he wrote a paper proposing the Law of Octaves -
Dimitri Mendeleev
In 1869, Russian chemist Dimitri Mendeleev produced a periodic table based on atomic weights. He found that the table showed similarities in vertical, horizontal, and diagonal. Elements with similar properties appeared under each other. He left room for elements that he knew where to be found. -
William Ramsay
William Ramsay discovered the Noble Gases. -
J.J Thomson
Thomson used a cathode ray tube to infer that there are small particles inside of every atom. This inference proved Dalton's theory to be wrong. Particles can be divided. Through this experiment Thomson also inferred that atoms must be negatively charged.Thomson purposed the plum pudding model which allowed scientefic advances to occur. -
Ernest Rutherford
Ernest Rutherford, British chemist and physicist, studied radiations emitted from uranium and thorium and named them alpha and beta. -
Hantaro Nagaoka
In 1904, Hantaro Nagaoka developed an early but incorrect planetary model of the atom. He based his model of the atom around the rings of the planet saturn. However his model was not created properly. He explained that the rings are held there due to its massive orbit. Although this model was wrong it still allowed for the discovery of the atoms shells. -
Henry Moseley
Henry Moseley determined the atomic number of each of the elements and modified the 'Periodic Law'. -
Neils Bohr
Neil suggested that electrons travel around the nucleus in definite paths. These paths are always at a certain "level" away from the nucleus. He also stated that electrons cannot travel in between each path, however they can jump from one path to another. -
Glenn Seaborg
Glenn Seaborg synthesised transuranic elements (the elements after uranium in the periodic table)
