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John Dalton
John Dalton's (1766-1844) contribution to the atomic theory was significant, his theory proposed several basic ideas: All matter is composed of atoms, atoms cannot be made or destroyed, all atoms of the same element are identical, chemical reactions occur when atoms are rearranged, compounds are formed from atoms of the constitutent elements. This ideas served as a base for further development of the atomic theory.
"John Dalton." Homepage of the Chemical Heritage Foundation. N.p., Web. 04 Sept. -
Dalton's Atomic Model
Dalton's model is one of the most fundamental of physics and chemistry. His model focuses on 5 laws; 1st: pure elements consist of particles called atoms, 2nd: atoms of an element are all the same for that element. 3rd: atoms of different elements can be told apart by their atomic weights, 4th: atoms of elements unit eto form chemical compounds. Finally, he states atoms can neither be created or destroyed in chemical reactions, only the grouping changes. -
William Crooke
William Crooke's (1832-1919) contribution to the atomic theory was significant, he discovered cathode rays which had the following properties: travel in straight lines from the cathode; cause glass to fluoresce; impart a negative charge to objects they strike; are deflected by electric fields and magnets to suggest a negative charge; cause pinwheels in their path to spin indicating they have mass. Later, this led to the discovery of electrons. -
Crooke's Tube and Cathode Rays
Crooke's tube and the cathode rays lead to the discovery of the electron, which profoundly influenced further atomic models. This discovery was made with the Crooke's Tube; he noticed that as you removed gas from a tube, a glow would appear if you place a high voltage across it.
Crookes noticed that a shadow would form if something was placed in the tube, so he believed some new kind of light was being produced, this were cathode rades. He discovered some objects can also have a negative charge. -
J. J. Thomson
Thomson made a great contribution to the atomic theory; in 1897 he discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube, an area being investigated by numerous scientists at the time. In his theory he suggested that an atom was a sphere of positively charged matter with negatively charged electrons surrounding them. He stated that electrons were also positioned by electrostatic forces. -
J.J Thomson's Model (Plum Pudding Atomic Model)
Thomson's atomic model was proposed in 1904. In this model, the atom is composed of electrons, yet Thomson still called them "corpuscles", surrounded by a soup of positive charge to balance the electrons negative charges, like negatively charged "plums" surrounded by positively charged "pudding". The electrons were thought to be positioned throughout the atom, but with many structures for positioning multiple electrons.
["Plum Pudding Model." Universe Today RSS. N.p., n.d. Web. 04 Sept. 2013.] -
Ernest Rutherford
Rutherford's atomic theory described the atom as having a central positive nucleus surrounded by negative orbiting electrons. It suggested that most of the mass of the atom was contained in the small nucleus, and the rest of the atom was mostly empty space. Rutherford came to this conclusion following results of his gold foil experiment. This involved the firing of radioactive particles through minutely thin metal foils (notably gold) and detecting them using screens coated with zinc sulfide. -
Rutherford Model
This model described the atom as a tiny, dense, positively charged core called a nucleus, in which nearly all the mass is concentrated, around which the light, negative constituents, called electrons, circulate at some distance, much like planets revolving around the Sun. The Rutherford atomic model has been alternatively called the nuclear atom, or the planetary model of the atom. -
Niels Bohr
Niels Bohr made several relvant contributions to the atomic theory. He was the first to discover that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element. He proposed the theory that electrons travel in discrete orbits around the atom's nucleus. Also the shell model of the atom; where the chemical properties of an element are determined by the electrons in the outermost orbit. -
Bohr Model + Quantum Mechanical Model
His model represents the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus which is similar to the solar system.
Since the Bohr model is a modification of the Rutherford model, many sources refer to it as the Rutherford-Bohr model.
First mod to present that electrons traveled in orbits around the atom's nucleus and that the chemical properties of the element was largely determined by the number of electrons in the outer orbits. -
James Chadwick
James Chadwick's contribution to the atomic theory was the discovery of the neutron; proving that it was the most sturdy particle launching nuclear reactions. He discovered it by realizing that the mass was more than the atomic mass and the electrons. He found out that the electrons had no input in the weight and that another particle was involved in making the atom. He realized that the atom contained neutral particles, thus discovering the neutron. -
James Chadwick Model
Chadwick's model was very similar to Bohr's Model, with a significant addition to it, his own discovery; the neutron. Such as Bohr's, it depicts the atom as small, positively charged nucleus surrounded by electrons and neutrons that travel in circular orbits around the nucleus. It is a quantum physical interpretation of Rutherfords model.
["Bohr Model." Wikipedia. Wikimedia Foundation, 29 Aug. 2013. Web. 04 Sept. 2013. http://en.wikipedia.org/wiki/Bohr_model.]
