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Thomson's Atomic Model

Negative electrons embedded in a positively charged sphere.

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Lightsabers and Chocolate Chip Ice Cream

So how is that lightsabers and chocolate chip ice cream relate?

Source: lightsaber: http://www.flickr.com/photos/mikey_blue_eyes/6915644490/sizes/l/ , chocchip ice cream: http://blogs.egusd.net/gaviolavictoria6/files/2013/03/chocchip-14y9l7f.jpg
License: CC BY-NC 3.0


Well, they don't really relate. But let’s use our knowledge of J.J. Thomson’s experiments with cathode ray tubes and his atomic model to make the connection.

Recall that J.J. Thomson discovered the presence of the electron, discrediting Dalton’s model of an indivisible solid atom. How did he do that? Using our analogy, let’s figure out how he got from "lightsabers" to "chocolate chip ice cream".

Creative Applications

First, let’s figure out how our analogy will correspond to Thomson’s famous experiment. Explain what the lightsaber represents and what the chocolate chip ice cream represents.

What would happen to the cathode lightsaber’s light if you placed a positive force to its left and a negative force to its right? What would this allow you to conclude about the ray of particles?

How did Thomson know that these particles are components of an atom, like the chocolate chips in chocolate chip ice cream? (hint: there was previous knowledge that the particles in the ray were 1,000 times smaller than hydrogen ions; also, Thomson observed the same stream of particles regardless of the type of metal used for the antode). Also, how did he know they were floating in a positive mass?

Now looking back and using other concepts we know from chemistry, can you explain how the ray of light was created in the cathode ray tube?


If you need to review the methods that Thomson used to study the effects of charges on the cathode ray and what led him to think there are negative electrons inside atoms, watch this video by Tyler DeWitt:

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  1. [1]^ Source: lightsaber: http://www.flickr.com/photos/mikey_blue_eyes/6915644490/sizes/l/ , chocchip ice cream: http://blogs.egusd.net/gaviolavictoria6/files/2013/03/chocchip-14y9l7f.jpg; License: CC BY-NC 3.0

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