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Development of the atomic theory4/7/2024 The atoms that make chemical compounds are present in set proportions.That atoms of the same element are of the same type and mass. That atoms are indivisible and invisible particles.In 1803, the English scientist John Dalton reworked Democritus' theory, as follows: In 1758, Roger Joseph Boscovich described a precursor of the atomic theory. They had no way to experiment to show whether his theory was true or not. Some other philosophers agreed, and others disagreed. Democritus thought that there was nothing between the atoms and that everything around us could be explained if we could understand how atoms worked. He thought that atoms would last forever, never change and could not be destroyed. Democritus called these small pieces of matter atoms, which means "indivisible". He said that this last piece of matter could not be cut any smaller. It does not apply in the same way to plasmas or neutron stars.ĭemocritus' atomic theory ĭemocritus thought that if you cut something in half again and again, you would at last have to stop. The theory applies to solids, liquids and gases. A lot of the ideas in the modern theory came from John Dalton, a British chemist and physicist. The first idea of the atom came from the Greek philosopher Democritus. These subatomic particles are made of quarks. However, it is now known that atoms are made of protons, neutrons, and electrons. Atoms were once thought to be the smallest pieces of matter. In chemistry and physics, the atomic theory explains how our understanding of the atom has changed over time. A Croatian Jesuit who provided a prototype of the atomic theory John Dalton (1766–1844), English chemist and physicist Sir Joseph John Thomson (1856–1940), English physicist, discovered the electron and its negative charge. 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.Democritus was a Greek philosopher, 460 BC Roger Joseph Boscovich. However, the positively charged part of an atom was not yet well understood. 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. 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. 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. \): Millikan’s experiment measured the charge of individual oil drops.
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