Thomson

The Cathode Ray Tube
In the 1890's, J. J. Thomson, who was studying the properties of electricity, came up with a new atomic model.
 * His work revolved around experiments with a cathode ray tube (CRT).


 * [|See the historical development] of cathode ray tubes.
 * [|Follow this link]to see a modern application of a cathode ray tube.
 * Two links on CRTs: [|magnetic field effects], and [|use in television].

His findings were twofold:
 * cathode rays were negatively charged particles (had an arbitrary net charge of -1 per particle) because they were repulsed by a negatively charged electric field. See [|this link for a demonstration of his experiments.]
 * these particles were fundamental parts of atoms, thus the need for modifying Dalton's first postulate and his atomic model. They also carried electromagnetic properties.

The "Plum Pudding" Atom
Thomson also experimented with how a beam of electrons interacted with a thin foil of metal (likely gold).

Since "like charges repel", the expectation was that the electron beam would be scattered by the electrons in the atom.

In reality, the beam remained relatively unchanged as its electrons passed through the foil. This was unexpected, and changed the atomic model drastically. It went from being a sphere of matter to a practically empty electric field containing diffused electrons.

Based on these findings, Thomson came up with his "[|plum pudding"] model of the atom.
 * Thomson's atomic model contained small particles of negative charge (later called electrons) moving about within a diffuse sphere of positive charge.

Mass Spectrometry
Thomson also built the first **mass spectrometer**. This device ionized atoms and then sent them through a magnetic field. The strength of the magnetic field allowed the calculation of an atom's mass. Thomson's spectrometry experiments with neon showed a double beam. This meant that neon was actually composed of two **isotopes**//**,**// each with a slightly different mass.