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Thomson Model of the Atom J. J. Thomson - English physicist. 1897 Made a piece of equipment called a cathode ray tube. It is a vacuum tube - all the air.

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Presentation on theme: "Thomson Model of the Atom J. J. Thomson - English physicist. 1897 Made a piece of equipment called a cathode ray tube. It is a vacuum tube - all the air."— Presentation transcript:

1 Thomson Model of the Atom J. J. Thomson - English physicist Made a piece of equipment called a cathode ray tube. It is a vacuum tube - all the air has been pumped out.

2 Source of Electrical Potential Metal Plate Gas-filled glass tube Metal plate Stream of negative particles (electrons) A Cathode Ray Tube Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 58

3 Background Information Cathode Rays Form when high voltage is applied across electrodes in a partially evacuated tube. Originate at the cathode (negative electrode) and move to the anode (positive electrode) Carry energy and can do work Travel in straight lines in the absence of an external field

4 A Cathode Ray Tube Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 58

5 Cathode Ray Experiment 1897 Experimentation Using a cathode ray tube, Thomson was able to deflect cathode rays with an electrical field. The rays bent towards the positive pole, indicating that they are negatively charged.

6 Dorin, Demmin, Gabel, Chemistry The Study of Matter, 3 rd Edition, 1990, page 117 The Effect of an Electric Field on Cathode Rays High voltage cathode source of high voltage positive plate negative plate anode _ +

7 Thomsons Experiment + - vacuum tube metal disks voltage source

8 Thomsons Experiment + - vacuum tube metal disks voltage source

9 Thomsons Experiment + - voltage source OFF ON Passing an electric current makes a beam appear to move from the negative to the positive end

10 Thomsons Experiment + - voltage source OFF ON

11 Thomsons Experiment + - voltage source OFF ON + - By adding an electric field… he found that the moving pieces were negative.

12 Cathode Ray Experiment Deflection region Drift region Displacement + - Anodes / collimators Cathode Volts

13 Thomsons Calculations Cathode Ray Experiment Thomson used magnetic and electric fields to measure and calculate the ratio of the cathode rays mass to its charge. Magnetic deflection charge of ray particle magnetic field length of deflection region length of drift region mass of ray particle velocity of ray particle x x x x = Electric deflection charge of ray particle electric field length of deflection region length of drift region mass of ray particle velocity of ray particle x x x x = 2 magnetic deflection electric deflection magnetic field electric field x velocity = Thomson PAPER

14 Conclusions He compared the value with the mass/ charge ratio for the lightest charged particle. By comparison, Thomson estimated that the cathode ray particle weighed 1/1000 as much as hydrogen, the lightest atom. He concluded that atoms do contain subatomic particles - atoms are divisible into smaller particles. This conclusion contradicted Daltons postulate and was not widely accepted by fellow physicists and chemists of his day. Since any electrode material produces an identical ray, cathode ray particles are present in all types of matter - a universal negatively charged subatomic particle later named the electron

15 Conclusiones He comparado con el valor de la masa / carga más ligera para la proporción de partículas cargadas. En comparación, Thomson calcula que las partículas de rayos catódicos pesaba 1 / 1000 tanto como el hidrógeno, el átomo más ligero. Él llegó a la conclusión de que los átomos contienen partículas subatómicas, átomos de dividirse en partículas más pequeñas. Esta conclusión es contradicha Dalton postulado y no fue ampliamente aceptada por sus compañeros físicos y químicos de su época. Dado que todo el material del electrodo produce una idéntica de rayos, rayos catódicos partículas están presentes en todos los tipos de materia, universal negativamente cargado de partículas subatómicas más tarde el nombre de electrón

16 Cathode Rays Cathode ray = electron Electrons have a negative charge Dorin, Demmin, Gabel, Chemistry The Study of Matter, 3 rd Edition, 1990, pages High voltage cathode source of high voltage yellow-green fluorescence shadow (A) The effect of an obstruction on cathode rays (B) The effect of an electric field on cathode rays High voltage cathode source of high voltage positive plate negative plate anode source of low voltage + -

17 J.J. Thomson He proved that atoms of any element can be made to emit tiny negative particles. From this he concluded that ALL atoms must contain these negative particles. He knew that atoms did not have a net negative charge and so there must be balancing the negative charge. J.J. Thomson

18 William Thomson (Lord Kelvin) In 1910 proposed the Plum Pudding model –Negative electrons were embedded into a positively charged spherical cloud. Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 56 Spherical cloud of Positive charge Electrons

19 Plum-Pudding Model Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 56

20 Thomson Model of the Atom J.J. Thomson discovered the electron and knew that electrons could be emitted from matter (1897). William Thomson proposed that atoms consist of small, negative electrons embedded in a massive, positive sphere. The electrons were like currants in a plum pudding. This is called the plum pudding model of the atom. - electrons

21 Other pieces Proton - positively charged pieces –1840 times heavier than the electron Neutron - no charge but the same mass as a proton. How were these pieces discovered? Where are the pieces?


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