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Atomic Theory Timeline

Published on Nov 18, 2015

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"Father of Modern Science"
(460 B.C. - 370 B.C.)
Accomplishments : introduces the atomic theory of the universe. Developed the idea of the Milky Way being a concentration of distant stars. Introduced Atomism and Etiology. Introduced the concept of different type of atoms. Solids being small and pointy, liquids being large and round, and oils and gas being made very small atoms that can easily slip past eachother.

(1743 - 1794)
Description: He discovered the role oxygen plays in combustion. He recognized and named oxygen and hydrogen and opposed the phlogiston theory. Lavoisier helped construct the metric system, wrote the first extensive list of elements, and helped to reform chemical nomenclature. He predicted the existence of silicon and was also the first to establish that sulfur was an element rather than a compound. He discovered that, although matter may change its form or shape, its mass always remains the same.

(1766 - 1844)
Accomplishments: Said that elements consisted of tiny particles called atoms. He stated an element is one of a kind because all atoms of an element are identical. All the atoms that make up the element have the same mass. All elements are different from each other due to differing masses.

Description: Antoine Lavoisier established that mass is neither created nor destroyed in any ordinary chemical reaction. That the mass of reacting substances (reactants) by a chemical reaction is always equal to the mass of the substances produced (products).

Description: John dalton proposed that-
1) All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms.

(1834 - 1907)
Accomplishments: He formulated the Periodic Law, created his own version of the periodic table of elements, and used it to correct the properties of some already discovered elements and to also predict the properties of eight elements yet to be discovered.

(1868 - 1953)
Accomplishments: Millikan began a series of experiments to determine the electric charge carried by a single electron. He began by measuring the course of charged water droplets in an electric field. The results suggested that the charge on the droplets is a multiple of the elementary electric charge. He also undertook a major study of the radiation that the physicist Victor Hess had detected coming from outer space. Millikan proved that this radiation is of extraterrestrial origin and named it “cosmic rays.”

(1870 - 1940)
Accomplishments: J.J. Thomson discovered electrons and noticed that an atom can be divided. Also, he concluded atoms are made of positive cores and negatively charged particles within it. He developed the Plum Pudding Model before the atomic nucleus was discovered. This model shows that the electron are surrounded by a "pudding" of positive charges to balance the negative charges

"Father of Nuclear Physics"
(1871 - 1937)
Accomplishments: He theorized that atoms have their charge concentrated in a very small nucleus, and constructed the Rutherford model of the atom. He constructed the Gold Foil Expirement and proved his theory of a concentrated charge in an atom, true. He is widely credited with first "splitting the atom" in a nuclear reaction between nitrogen and alpha particles, in which he also discovered and named the proton.

(1885 - 1962)
Accomplishments: Bohr developed the Bohr model of the atom, in which he proposed that energy levels of electrons are discrete and that the electrons revolve in stable orbits around the atomic nucleus, but can jump from one energy level to another. He conceived the principle of complementarity: that items could be separately analysed in terms of contradictory properties, like behaving as a wave or a stream of particles.

(1887 - 1915)
Accomplishments: He proposed that the atom contains in its nucleus a number of positive nuclear charges that is equal to its atomic number in the periodic table. Moseley's Law justified many concepts in chemistry by sorting the chemical elements of the periodic table of the elements in a logical order based on their physics.

(1887 - 1961)
Accomplishments: He formulated the wave equation and revealed the identity of his development of the formalism and matrix mechanics. He was the author of many works in various fields of physics: statistical mechanics and thermodynamics, physics of dielectrics, colour theory, electrodynamics, general relativity, and cosmology.

"father of nuclear physics"
(1891 - 1974)
Accomplishments: Chadwick discovered the neutron. He anticipated that neutrons would become a major weapon in the fight against cancer. He was Rutherford's assistant director of research at the Cavendish Laboratory for over a decade at a time when it was one of the world's foremost centres for the study of physics. He also wrote the final draft of the MAUD Report, which inspired the U.S. government to begin serious atomic bomb research efforts.

Preformed: (1897)
Description: His first experiment was to build a cathode ray tube with a metal cylinder on the end. This cylinder had two slits in it, leading to electrometers, which could measure small electric charges. He found that by applying a magnetic field across the tube, there was no activity recorded by the electrometers and so the charge had been bent away by the magnet. This proved that the negative charge and the ray were inseparable and intertwined.

Description: The plum pudding model was a model of the atom that incorporated the recently discovered electron, and was proposed by J. J. Thomson in 1904. Thomson had discovered the electron in 1897. The plum pudding model was abandoned after discovery of the atomic nucleus. The plum pudding model of the atom is also known as the blueberry muffin model or the raisin bun model.

Preformed: (1908 - 1913)
Description: Ernest Rutherford studied the absorption of radioactivity by thin sheets of metal foil and found two components: alpha radiation, which is absorbed by a few thousandths of a centimeter of metal foil, and beta radiation, which can pass through 100 times as much foil before it was absorbed.

Description: Rutherford's model for the atom contained the new features of a relatively high central charge concentrated into a very small volume in comparison to the rest of the atom, and with this central volume also containing the bulk of the atomic mass of the atom, This region would be named the "nucleus" of the atom in later years.

Description: The quantum mechanical model was invented by Niels Bohr and is based on mathematics. It is based on quantum theory, which says matter also has properties associated with waves. The quantum mechanical model of the atom uses orbitals and volumes of space in which there is likely to be an electron.

Description: In atomic physics, the Rutherford–Bohr model or Bohr model, introduced by Niels Bohr in 1913, depicts the atom as a small positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus; similar in structure to the solar system, but with attraction provided by electrostatic forces rather than gravity. After the cubic model , the plum-pudding model , the Saturnian model, and the Rutherford model came the Rutherford–Bohr model or just Bohr model for short.

Description: Erwin Schrodinger built upon the thoughts of Bohr. He developed the probability function for the Hydrogen atom (and a few others). The cloud model represents a sort of history of where the electron has probably been and where it is likely to be going.