| Date | Event |
|---|
| 400 B.C. |
Democritus (400 B.C.)Democritus proposed that matter was composed of tiny indivisible particles. He coined the term átomos, which means "uncuttable" or "the smallest indivisible particle of matter" in greek. |
| 1704 |
Isaac Newton
In 1704, Sir Isaac Newton, an English physicist and mathematician proposed a mechanical universe with small, solid masses in motion. |
| 1803 |
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 chemical compounds.
- In chemical reactions, atoms are combined, separated, or rearranged.
|
| 1832 |
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 to their equivalent weights.
Electrolysis is a method of using a direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction
Electrolysis is the passage of a direct electric current through an ionic substance that is either molten or dissolved in a suitable solvent, resulting in chemical reactions at the electrodes and separation of materials.
|
| 1859 |
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. |
| 1869 |
Dmitri Mendeleev
Dmitri Ivanovich Mendeleev was a Russian chemist and inventor. In 1869, Dmitri Mendeleev created the first version of the periodic table of elementsof all known elements and predicted several new elements to complete the table. |
| 1873 |
James Clerk Maxwell
James Clerk Maxwell was a Scottish theoretical physicist. In 1873, he formulated classical electromagnetic theory and made quantitative connection between light and electromagnetism. |
| 1874 |
G.J. Stoney
G.J. Stoney was an Anglo-Irish physicist. He proposed that electricity was made of discrete negative particles and proposed the term electron to describe the fundamental unit of electrical charge. |
| 1879 |
Sir William Crookes
Sir William Crookes, was a British chemist and physicist worked on spectroscopy. He developed the Crookes tubes, investigating cathode rays. In his investigations of the conduction of electricity in low pressure gases, he discovered that as the pressure was lowered, the negative electrode (cathode) appeared to emit cathode rays. |
| 1886 |
E. Goldstein
In 1886, E. Goldstein, a German physicist discovered that tubes with a perforated cathode also emit a glow at the cathode end. Goldstein concluded that in addition to cathode rays, there is another ray that travels in the opposite direction. Goldstein called them canal rays. |
| 1895 |
Wilhelm Roentgen
Wilhelm Roentgen, a German physicist, on 1895, produced and detected electromagnetic radiation in a wavelength range today known as X-rays. |
| 1896 |
Henri Becquerel
French physicist Antoine Henri Becquerel discovered radioactivity while working with uranium salts, which might emit penetrating X-ray-like radiation when illuminated by bright sunlight. |
| 1897 |
J.J. Thomson
The British physicist J. J. Thomson discovered the electron in the year 1897. Thomson used a cathode ray tube for his experiment. |
| 1898 |
Ernest Rutherford
Ernest Rutherford, British chemist and physicist, studied radiations emitted from uranium and thorium and named them alpha and beta. |
| 1898 |
Marie Sklodowska Curie Marie Skłodowska-Curie, Polish physicist and chemist, discovered the radioactive elements polonium and radium. She coined the term radioactivity. |
| 1900 |
Max Planck
In 1901 Max Planck, German physicist, proposed a theory that energy did not flow in a steady continuum, but was delivered in discrete packets. Planck later called discrete units of energy as quanta. |
| 1900 |
Frederick Soddy
Frederick Soddy was an English radiochemist and monetary economist. In 1900, he explained, with Ernest Rutherford, that radioactivity is due to the transmutation of elements. In 1913 he concluded that elements might exist in forms of different atomic weights though the chemical properties are identical. He named this concept isotope meaning 'same place'. |
| 1903 |
Hantaro Nagaoka
Hantaro Nagaoka, Japanese physicis, proposed an atomic model in which a positively charged center is surrounded by a number of revolving electrons, in the manner of Saturn and its rings. |
| 1904 |
Richard Abegg
Richard Wilhelm Heinrich Abegg was a German chemist and researcher of valence theory. He proposed that the difference of the maximum positive and negative valence of an element tends to be eight. This is known as Abegg's rule. |
| 1905 |
Albert Einstein
Albert Einstein was a German physicist. In 1905 Albert Einstein formulates Theory of Relativity. He published law of mass-energy equivalence through his famous formula E=mc². |
| 1906 |
Hans Geiger
Hans Geiger was a German physicist. He developed a detector known as the Geiger counter to detect individual alpha particles and other ionizing radiations. |
| 1909 |
R.A. Millikan
In 1909, R.A. Millikan, American physicist suggested that the charge on the water droplets is a multiple of the elementary electric charge. In 1910, he conducted oil-drop experiment in which he replaced water with oil and obtained more precise results. |
| 1911 |
Ernest Rutherford
In 1911, Ernest Rutherford developed the "gold foil experiment". Rutherford deteremined that the nucleus of an atom is very dense and has a positive charge. |
| 1914 |
H.G.J. Moseley
H.G.J. Moseley, an English physicis, conducted experiments on x-ray spectra and discovered The atomic number of an element is equal to the number of protons in the nucleus. This is known as Moseley's law. |
| 1919 |
Francis William Aston
In 1919, Francis William Aston, British physicist, discovered of a large number of isotopes using a mass spectrometer. |
| 1922 |
Neils Bohr
Neils Bohr, Danish physicist, developed the model of the atom with the nucleus at the center and electrons in orbit around it, which he compared to the planets orbiting the sun. This model is known as "Planetary Model".
He proposed Quantam theory that electrons move from one energy level to another in discrete steps, not continuously. |
| 1923 |
Louis de Broglie
In 1923 Louis de Broglie, French physicist discovered of the wave nature of electrons. |
| 1926 |
Erwin Schrodinger
Edwin Schrodinger, an Austrian physicist suggested that electrons were arranged in orbitals which were systematically distributed within Electron Clouds. He defined an orbital as the region around the nucleus in which two electrons may randomly move. |
| 1927 |
Werner Heisenberg
Werner Heisenberg, German physicist discovered a way to formulate quantum mechanics in terms of matrices. He proposed uncertainty principle which states that the position and the velocity of an object cannot both be measured exactly, at the same time. |
| 1930 |
Paul Dirac
Paul Dirac, English physicist predicted of the existence of antiparticles. |
| 1932 |
John Douglas Cockcroft/ Ernest Thomas Sinton Walton
In 1932 Cockcroft and Walton designed the Cockcroft-Walton generator and used it to disintegrate lithium atoms by bombarding them with protons. |
| 1932 |
James Chadwick
In 1932 James Chadwick, English physicist discovered neutron in the atomic nucleus. |
| 1936 |
Ernest Lawrence
Ernest Orlando Lawrence, American physicist, invented the cyclotron, the first particle accelerator to achieve high energies. |
| 1938 |
Lise Meitner, Otto Hahn and Fritz Strassmann
In 1938 Otto Hahn, Lise Meitner, and Fritz Strassmann detected the element barium after bombarding uranium by neutrons. Lise Meitner interpreted their results as nuclear fission. |
| 1941-51 |
Glenn Seaborg
Glenn Seaborg, an American scientist discovered transuranium elements, and developed the actinide concept, which led to the current arrangement of the actinide series in the periodic table of the elements. |
| 1942 |
Enrico Fermi
Enrico Fermi, an Italian physicist, conducted the first controlled chain reaction releasing energy from the atoms nucleus. He worked on the development of Chicago Pile-1, the first nuclear reactor, and he contributions to the development of quantum theory, nuclear and particle physics, and statistical mechanics. |