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History of the Atom. Part II. Joseph John Thomson. 1897 - Discovers the Electron Experimented with cathode rays Took a glass tube and pumped most of the air out of it. Applied a high voltage that traveled from the negative cath ode to the positive anode.
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History of the Atom Part II
Joseph John Thomson 1897 - Discovers the Electron • Experimented with cathode rays • Took a glass tube and pumped most of the air out of it. • Applied a high voltage that traveled from the negative cathode to the positive anode. • The radiation that was produced from this high voltage is known as a cathode ray.
Thomson continued • In his first experiment he deflected the cathode ray by introducing a magnetic field. • In his second experiment he deflected the cathode ray by introducing an electric field. • From these experiments he determined that the particles in the cathode ray were negatively charged particles emitted by atoms called electrons.
Thomson Continued • Thomson concluded that the atom was a positively charged mass that was filled with these tiny negatively charged electrons. • This model of the atom is referred to as the plum pudding model.
Robert Millikan 1909 - calculated the charge of an electron • Small droplets of oil were dropped between electrically charged plates. • Millikan was able to determine the charge by varying the voltage of the plates and observing how it effected the rate of falling. • Determine the charge to be 1.602 x 10-19 Coulomb.
Ernest Rutherford 1910 – Credited with the discovery of the proton • Worked on his gold foil experiment with Geiger and Marsden. • Noticed that when alpha particles were aimed at a piece of gold foil, most of them passed through but with a small amount deflected back.
Rutherford continued • Rutherford’s gold foil experiment provided data that was inconsistent with Thomson’s cathode ray experiment. • Rutherford explained his results by stating that the atom had an extremely dense region called the nucleus. He stated that most of the atom was empty space in which the electrons orbited this nucleus.
Niels Bohr 1913 - Established that the electrons were spinning in orbits • Refined Rutherford’s idea of electrons rotating around a dense nucleus. • Determined that the orbits could only contain a set number of electrons
Bohr Continued • Used Planck’s constant, developed by Max Planck to determine that electrons were orbiting at different energy levels. • Electrons can gain or lose energy by jumping from different energy levels • h is Planck’s constant.
Erwin Schrödinger 1926 - Schrödinger developed the Quantum Mechanical Model of the Atom. • Looking at Bohr’s model, he used mathematical equations to determine the likelihood of finding an electron in a certain position. • In this view of the atom, electrons are orbiting the nucleus in different energy level, orbitals with varying spatial arrangements.
James Chadwick 1932 – Discovered the neutron • Smashed alpha particles into Beryllium • The radiation that was released hit hydrogen atoms in paraffin wax and sent them to a detecting chamber. (This could only happen if the particles that were released from radiation were the same size as a hydrogen atom. )
