Thomson’s “Plum Pudding” Model or the Discovery of the Electron!
As scientists discovered more elements in the 19th century, they began to speculate whether the atom itself had constituent parts. Around this time, advances in technology allowed for new experiments based upon glass tubes evacuated of air. Michael Faraday first discovered that when an electric voltage was placed across these tubes, the positively charged end of the tube began to glow. Further experimentation revealed that an invisible beam was passing from the negatively charged end (the cathode) of the tube to the positively charged end (the anode). This phenomenon became known as a cathode ray. Until LCD and plasma screen technology became commercially accessible within the past decade, most television sets and computer monitors used cathode rays to produce images on a screen.
Experiments on cathode ray tubes continued during the second half of the 19th century. At the time, atoms were still believed to be the smallest unit of matter, and some scientists hypothesized that cathode rays consisted of electrically charged atoms. In 1897, J. J. Thomson first measured the mass of a cathode ray particle, and discovered that it was about 1800 times less massive than the lightest known atom, hydrogen. Thomson correctly deduced that these particles, later known as electrons, were a smaller component of the atom. Although Thomson was not the first to experiment with cathode rays, he is credited with the discovery of the electron because he was the first to put forward the idea that they were constituent particles of the atom.
Thomson’s discovery of the electron led him to propose a new atomic model, which consisted of a positively charged sphere with smaller negatively charged electrons scattered throughout it. Because of the electrons’ similarity in this model to plums or raisins suspended in pudding, this became popularly known as the “plum pudding” model of the atom.
Experiments on cathode ray tubes continued during the second half of the 19th century. At the time, atoms were still believed to be the smallest unit of matter, and some scientists hypothesized that cathode rays consisted of electrically charged atoms. In 1897, J. J. Thomson first measured the mass of a cathode ray particle, and discovered that it was about 1800 times less massive than the lightest known atom, hydrogen. Thomson correctly deduced that these particles, later known as electrons, were a smaller component of the atom. Although Thomson was not the first to experiment with cathode rays, he is credited with the discovery of the electron because he was the first to put forward the idea that they were constituent particles of the atom.
Thomson’s discovery of the electron led him to propose a new atomic model, which consisted of a positively charged sphere with smaller negatively charged electrons scattered throughout it. Because of the electrons’ similarity in this model to plums or raisins suspended in pudding, this became popularly known as the “plum pudding” model of the atom.
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Do NOT try this at home!! See below!
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