The Raisin Pudding Model of the Atom (Wilhelm Wien)
By 1898 Wilhelm Wien was able to show that canal rays could be deflected by both magnetic and electric fields, as would be expected for particles that carry an electric charge. They were deflected, however, in the direction expected for positively charged particles.
These observations can be explained by assuming that the atoms or molecules in the gas in a cathode-ray tube lose one or more electrons when excited by the voltage applied to the electrodes of the tube. The negatively charged electrons flow toward the anode. The positive ions formed when the atoms or molecules lose electrons flow in the opposite direction.
The charge-to-mass ratio for the cathode rays is always the same because they consist of negatively charged electrons. The charge-to-mass ratio for the positively charged canal rays depends on the gas used to fill the tube because the nature of the ions produced when the atoms or molecules lose electrons depends on the identity of the gas.
|History of Chemistry|