Particle theory of matter

[leidiot]

My teacher has asked me to do some reseach on the history of the particle theory of matter. i can't find anything. Do you guys know anything about the history of it?

[insane_alien]

look up "rutherford" on google.

[Klaynos]

"gold foil defraction" might also be another usefull search term, or possibly "historical atomic models"

[timo]

Above two answers are related to the "Rutherford Experiment" which demonstrated that an Atom has a small charged hard core - possibly even that this core is positively charged, but I´m not sure about that.

A step ahead of this is the proof that matter is actually made of atoms. I think that Brownian Motion was an important dicovery for the atom-model to come to a breakthrough. So http://en.wikipedia.org/wiki/Brownian_motion might be another interesting read for you.

[insane_alien]

yeah it shows the core is positively charged as it is alpha pariticles that it deflects. Suprised that you weren't sure on that one athiest being a physics expert and all...

[timo]

yeah it shows the core is positively charged as it is alpha pariticles that it deflects. Suprised that you weren't sure on that one athiest being a physics expert and all...

I am still not sure on it. Imho, a negatively charged core would have mostly the same effect - it also scatters alpha particles. I think the question is whether you can determine the charge-sign from the angular distribution and/or absorbtion rate of the alphas.

If you know the calculation showing that the different trajectories for equally-charged and oppsitely-charged cases result in a measurably different angular distribution for the scattered alphas, please post it here.

[swansont]

Electrons were already known to exist. Since an atom is neutral, the rest of the atomic material has to be positively charged.

[timo]

I do not know which knowledge was available in Rutherford´s time. What excluded the possibility of having a small hard core of electrons and some positive charges floating around, for example? Even if there was a reason to exclude it, it doesn´t solve the question whether the charge-sign of the hard core can be determined from the Rutherford experiment.

But since Swansont mentioned it: The electron probably also was an important discovery. The "Millikan Experiment" played an important role, I think.

[swansont]

I do not know which knowledge was available in Rutherford´s time. What excluded the possibility of having a small hard core of electrons and some positive charges floating around' date=' for example? Even if there was a reason to exclude it, it doesn´t solve the question whether the charge-sign of the hard core can be determined from the Rutherford experiment.

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JJ Thomson had discovered the electron about 10 years earlier (Rutherford had been his student) and had proposed the "Plum Pudding" model of the atom about a year before the alpha experiment.

[NeonBlack]

You might also want to include some of these things:

 

The ancient Greeks first proposed a small indivisible particle of matter. In fact, I think the word atom comes from ancient Greek.

 

I think John Dalton or Thomas Dalton or something like that came up with the first real atomic theory. He proposed that all elements are made of atoms and other compounds could be formed from combinations of atoms. I think he proposed this after he discovered that water is always made of 80% oxygen and 20% hydrogen.

 

Then, I think the electron was first discovered by cathrode-ray experiments, I'm not sure though.

 

As was mentioned earlier, The atomic nucleus was discovered by the gold foil experiments.

 

Probably the last thing (unless you're going for extra credit) might be Planck's experiments and the photon.

 

Hope this helps!

[leidiot]

I think John Dalton or Thomas Dalton or something like that came up with the first real atomic theory.

How about previous theories.

 

by the way. Thanks for helping guys:-)