1. Atomic Structure http://en.wikibooks.org/wiki/High_School_Che mistry/Further_Understanding_of_the_Atom

2. Dalton's Atomic Theory Held up well to a lot of the different chemical experiments that scientists performed to test it. In fact, for almost 100 years, it seemed as if Dalton's Atomic Theory was the whole truth. As it turns out, Dalton had a lot right. He was right in saying matter is made up of atoms He was right in saying there are different kinds of atoms with different mass and other properties He was "almost" right in saying atoms of a given element are identical He was right in saying during a chemical reaction, atoms are merely rearranged He was right in saying a given compound always has atoms present in the same relative numbers. But he was wrong in saying atoms were indivisible or indestructible.

3. J.J. Thompson In 1897, a scientist named J. J. Thompson conducted some research which suggested that Atomic Theory wasn’t the entire story. As it turns out, atoms are divisible. In fact, atoms are composed of smaller subatomic particles.

4. Discovering Electrons In the mid-1800s, scientists were beginning to realize that the study of chemistry and the study of electricity were actually related. First, a man named Michael Faraday showed how passing electricity through mixtures of different chemicals could cause chemical reactions. Shortly after that, scientists found that by forcing electricity through a tube filled with gas, the electricity made the gas glow! Scientists didn't, however, understand the relationship between chemicals and electricity until a British physicist named J. J. Thomson began experimenting with what is known as a cathode ray tube. Cathode Ray Tube Experiment

7. J. J. Thomson made a radical proposal: Maybe atoms are divisible! J. J. Thomson suggested that the small, negatively charged particles making up the cathode ray were actually pieces of atoms. He called these pieces "corpuscles", although today we know them as "electrons". Thanks to his clever experiments and careful reasoning J. J. Thomson is credited with the discovery of the electron.

8. Thomson's Model of the Atom Thomson's "plum-pudding" model for the atom. Notice how the "plums" are the negatively charged electrons, while the positive charge is spread throughout the entire pudding batter.

9. Thomson's Model of the Atom Negative electrons = Pieces of Fruit-Plums (chocolate chips) Positive material = Pudding (cookie dough batter) How this fits Thompson’s Observations: – Isolated electrons using a cathode ray tube – Never managed to isolate positive particles Result: Thomson theorized that the positive material in the atom must form something like the "batter" in a plum pudding, while the negative electrons must be scattered through this "batter".