John Thompson And John Dalton: The First Atomic Model

1041 Words 5 Pages
The first atomic model was introduced by an English chemist, physicist, and meteorologist named John Dalton. John Dalton had reintroduced the idea of the atom that had once been a theory of a Greek scientist named Democritus. However, unlike Democritus, Dalton was able to prove the existence of atoms. Through many experiments, Dalton came up with a list of properties, that he thought, all atoms shared.
Each element is composed of atoms
Atoms are tiny, featureless spheres
All atoms of same element are identical in mass
Compounds form when atoms of multiple elements combine
A given compound always has some relative number and kinds of atoms
The total mass after a reaction is the same as the total mass before the reaction.
Dalton’s assumption
…show more content…
His new model better described the structural components of the atom than Dalton’s featureless atom. Thompson used a Cathode Ray Tube, which was a sealed glass container, and shot a stream of electrons across the glass tube. When the particles stuck to the other end of the tube, it created a patch of light that indicated where the particles landed. Thompson discovered that by using a magnetic field, he could move and deflect particles. He found that particles would always move towards the positively charged side. By using a Cathode Ray Tube, Thompson was able to conclude that some particles are negatively charged; therefore, discovering electrons. Thompson 's Plum Pudding Model showed that electrons were distributed throughout the atom and that the rest of the atom would be positively …show more content…
Rutherford performed an experiment called the Gold Foil Experiment were fired alfa particles through a small slit at a very thin sheet of gold foil. Alfa particles are relatively massive particles travelling at a high speed so Rutherford thought all of the Alfa particles would pass through the gold foil. This is assumption was based off of JJ Thompson’s Plum Pudding Model that showed that electrons were dispersed evenly inside the atom and that the remaining parts of the atom were positively charged. Because the atom was said to be mainly positively charged particles, Rutherford did not think there would be much interference. Most of the particles proved to fit this theory by passing through the gold foil, however, some were scattered and deflected backwards. Rutherford had to alter the previous model to fit with his newfound discoveries. The reason the majority of the alfa particles were able to pass through the sheet of gold foil without being deflected was because the atom consists of mostly empty space. Rutherford also believed there had to have been a massive positively charged particle in the center of the atom and that the electrons revolved around the central particle instead of being dispersed throughout. These particles are responsible for the scattering deflecting of the alfa particles when shot through the gold foil. Rutherford’s

Related Documents