Thomson Model of the Atom : 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 has been pumped out.
A Cathode Ray Tube : A Cathode Ray Tube Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 58
Background Information : 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
A Cathode Ray Tube : A Cathode Ray Tube Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 58
Cathode Ray Experiment : 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.
The Effect of an Electric Field on Cathode Rays : Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 117 The Effect of an Electric Field on Cathode Rays
Thomson’s Experiment : Thomson’s Experiment + - vacuum tube metal disks voltage
source
Thomson’s Experiment : Thomson’s Experiment + - vacuum tube metal disks voltage
source
Thomson’s Experiment : Thomson’s Experiment + - voltage
source OFF ON Passing an electric current makes a beam appear
to move from the negative to the positive end
Thomson’s Experiment : Thomson’s Experiment + - voltage
source OFF ON
Thomson’s Experiment : Thomson’s Experiment + - voltage
source OFF ON By adding an electric field… he found that the moving pieces were negative.
Slide 12 : Cathode Ray Experiment Deflection
region Drift region Displacement + - Anodes / collimators Cathode Volts
Slide 13 : Thomson’s Calculations Cathode Ray Experiment
Thomson used magnetic and electric fields to measure and calculate the ratio of the cathode ray’s mass to its charge. Thomson
PAPER
Conclusions : 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 Dalton’s 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
Conclusiones : 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
Cathode Rays : Cathode Rays Cathode ray = electron
Electrons have a
negative charge Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, pages 117-118 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
J.J. Thomson : 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
William Thomson (Lord Kelvin) : 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
Plum-Pudding Model : Plum-Pudding Model Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 56
Thomson Model of the Atom : 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 - - - - - - -
Other pieces : 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?