 Joseph John Thomson, an English scientist, provided the first hint that an atom is made of even smaller particles.  He observed that there are NEGATIVELY.

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Presentation transcript:

 Joseph John Thomson, an English scientist, provided the first hint that an atom is made of even smaller particles.  He observed that there are NEGATIVELY CHARGED and POSITIVELY CHARGED particles in the atom.

 In 1987, he proposed a model of the atom that is sometimes called the plum pudding model (something like a raisin bread).  In this model the electrons (raisins) and protons (pudding) are uniformly mixed throughout the atom.

The 1904 Thomson model was disproved by the 1911 experiment, which was interpreted by Ernest Rutherford

 In 1911, British physicist Ernest Rutherford presented a new theory about the structure of the atom.  He reasoned that all of an atom’s positively charged particles were contained at the center, which he then called NUCLEUS.

 Ernest Rutherford publishes his atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons.  The electrostatic force of attraction between electrons and nucleus was likened to the gravitational force of attraction between the revolving planets and the Sun.electrostatic forcegravitational force  This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space.

 The scattering of alpha particles was due to the strong [electrostatic repulsion]which the alpha particles experienced when they approached the positive nucleus. The closer the approach, the greater the scattering.electrostatic repulsion

Explanation of Alpha-Scattering Results Plum-pudding atom Alpha particles Nuclear atom Nucleus Thomson’s modelRutherford’s model

Results of foil experiment if plum- pudding had been correct. Electrons scattered throughout positive charges Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page

Interpreting the Observed Deflections Dorin, Demmin, Gabel, Chemistry The Study of Matter, 3 rd Edition, 1990, page gold foil deflected particle undeflected particles.. beam of alpha particles.

In a ¼ sheet of paper: How did Rutherford's model of the atom differ from Thomson's model?