Thomson’s experiment of the charge-to-mass ratio of
cathode rays (1897) effectively indicated that, with any type of metal used as
the cathode, identical cathode rays were obtained. Knowing that cathode rays
were negatively charged particles—electrons—he proposed that atoms must all
contain these common particles. The puzzle was, if all atoms were to contain
electrons, how should these electrons be arranged inside the atoms?
cathode rays (1897) effectively indicated that, with any type of metal used as
the cathode, identical cathode rays were obtained. Knowing that cathode rays
were negatively charged particles—electrons—he proposed that atoms must all
contain these common particles. The puzzle was, if all atoms were to contain
electrons, how should these electrons be arranged inside the atoms?
Thomson developed his model where the atom was still assumed to be
spherical in shape. However, this time the electrons were proposed to embed and
scatter randomly among the region of the atom. Since the atom needed to be neutral
overall, there must be positive charge to balance the negative electron
charges. He proposed that the rest of the atom was uniformly positively
charged, with its mass evenly distributed but low in density. This model was
analogous to a plum pudding, where the electrons were like plums scattered throughout
the ‘pudding-like’ atom.
spherical in shape. However, this time the electrons were proposed to embed and
scatter randomly among the region of the atom. Since the atom needed to be neutral
overall, there must be positive charge to balance the negative electron
charges. He proposed that the rest of the atom was uniformly positively
charged, with its mass evenly distributed but low in density. This model was
analogous to a plum pudding, where the electrons were like plums scattered throughout
the ‘pudding-like’ atom.
