![]() This beam was deflected toward the positive charge and away from the negative charge, and was produced in the same way with identical properties when different metals were used for the electrodes. When high voltage was applied across the electrodes, a visible beam called a cathode ray appeared between them. Fletcher’s work on the oil drop project, however, was not recognized. This apparatus consisted of a sealed glass tube from which almost all the air had been removed the tube contained two metal electrodes. Robert Millikan was the sole recipient of the Nobel Prize in Physics in 1923 for both his work in this classic experiment and his research in the photoelectric effect. If matter were composed of atoms, what were atoms composed of? Were they the smallest particles, or was there something smaller? In the late 1800s, a number of scientists interested in questions like these investigated the electrical discharges that could be produced in low-pressure gases, with the most significant discovery made by English physicist J. While the historical persons and dates behind these experiments can be quite interesting, it is most important to understand the concepts resulting from their work. ![]() Here, we will discuss some of those key developments, with an emphasis on application of the scientific method, as well as understanding how the experimental evidence was analyzed. ![]() Much of this came from the results of several seminal experiments that revealed the details of the internal structure of atoms. In the two centuries since Dalton developed his ideas, scientists have made significant progress in furthering our understanding of atomic theory. And if atoms are neither created nor destroyed during a chemical change, then the total mass of matter present when matter changes from one type to another will remain constant (the law of conservation of matter). For example, if an element such as copper consists of only one kind of atom, then it cannot be broken down into simpler substances, that is, into substances composed of fewer types of atoms. (credit copper: modification of work by ).ĭalton’s atomic theory provides a microscopic explanation of the many macroscopic properties of matter that you’ve learned about. His earliest major success was the accurate determination of the charge carried by an electron, using the elegant falling-drop method he also proved that this quantity was a constant for all electrons (1910), thus demonstrating the atomic structure of electricity. ![]() \): When the elements copper (a shiny, red-brown solid, shown here as brown spheres) and oxygen (a clear and colorless gas, shown here as red spheres) react, their atoms rearrange to form a compound containing copper and oxygen (a powdery, black solid). ![]()
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