He believed that all elements are composed of atoms. Atoms are invisible and indestructible particles. Atoms of the same element are exactly alike,but atoms of different elements are different. Components are formed by joining of atoms of two or more elements. John Dalton is also credited with developing laws for understanding how gases work. In time, this would lead him to conclude things about how atoms interacted, the weight of atoms, and to design laws that establish atomic theory as scientific discipline.
Thomson discovered the electron and then went on to propose a model for the structure of the atom. His work also led to the invention of the mass spectrograph.
I have discovered negatively charged electrons using a cathode ray tube. Studying the passage of an electric current through a gas-filled tube, a beam of light was emitted. Thomson placed a magnet around the cathode ray tube causing the light beam to bend. This showed that the particles making up the beam were charged and they were affected by the magnet's magnetic field. My atomic model will be called the "plum pudding" model.
I fired a stream of tiny positively charged alpha (helium) particles at a very thin sheet of gold foil. I predicted that the particles would move just a few degrees from their paths as they all passed through. Instead, the actual results showed a number of particles repelled at almost 180 degrees off of the foil while most passed straight through the foil.
Ernest Rutherford's famed Gold Foil Experiment of 1909 demonstrated that atoms were made up of a charged nucleus orbited by electrons. While electrons had been described prior to this experiment, Rutherford was the first person to describe the existence of a small, charged atomic nucleus.