4/5/2024 0 Comments Development of atomic theory![]() In 1904, Thomson proposed the “plum pudding” model of atoms, which described a positively charged mass with an equal amount of negative charge in the form of electrons embedded in it, since all atoms are electrically neutral. However, it was eventually revised as new discoveries were made, particularly with regards to the structure of the nucleus and the discovery of isotopes. However, the positively charged part of an atom was not yet well understood. Thomson’s Atomic Theory helped to pave the way for further discoveries in atomic theory, including the development of the nuclear model of the atom by Rutherford and others. Scientists had now established that the atom was not indivisible as Dalton had believed, and due to the work of Thomson, Millikan, and others, the charge and mass of the negative, subatomic particles-the electrons-were known. (c) In the cathode ray, the beam (shown in yellow) comes from the. ![]() (b) This is an early cathode ray tube, invented in 1897 by Ferdinand Braun. Thomson produced a visible beam in a cathode ray tube. Since the charge of an electron was now known due to Millikan’s research, and the charge-to-mass ratio was already known due to Thomson’s research (1.759 10 11 C/kg), it only required a simple calculation to determine the mass of the electron as well. The results of these measurements indicated that these particles were much lighter than atoms (Figure 2.2.1 2.2. ![]() Millikan concluded that this value must therefore be a fundamental charge-the charge of a single electron-with his measured charges due to an excess of one electron (1 times 1.6 10 −19 C), two electrons (2 times 1.6 10 −19 C), three electrons (3 times 1.6 10 −19 C), and so on, on a given oil droplet. Looking at the charge data that Millikan gathered, you may have recognized that the charge of an oil droplet is always a multiple of a specific charge, 1.6 10 −19 C. The tabulated data are examples of a few possible values. First published in 1807, many of Dalton’s hypotheses about the microscopic features of matter are still valid in modern atomic theory. \): Millikan’s experiment measured the charge of individual oil drops. atomic theory, ancient philosophical speculation that all things can be accounted for by innumerable combinations of hard, small, indivisible particles (called atoms) of various sizes but of the same basic material or the modern scientific theory of matter according to which the chemical elements that combine to form the great variety of substa.
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