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Progress and Problems

So, here’s what we had so far: ancient people coming up with the idea of atoms, Dalton realizing it makes sense and publishing the first atomic theory, Thomson revolutionizing this theory and proving the existence of a subatomic level, and finally Rutherford discovering the nucleus.

Now, before we go on to Mr. Bohr’s doings and a whole new atomic model, we have to cover a few other things that happened in between. Cool stuff, like discoveries of isotopes, protons, neutrons, and atomic pretzels. Well, maybe not atomic pretzels, but that would be tasty…

Isotopes- Dalton’s wrong, again

As you’ll recall, one of the points in Dalton’s atomic theory stated that all atoms of the same elements are identical and have the same mass. And just like they did with the indivisibility section of his theory, scientists set out to prove that once again, Dalton is an idiot. I mean, an absolute genius, but an idiotic one.

Frederick Soddy, in 1913, was trying to experiment with radioactive decay trying to fill up the periodic table. He found that different elements seem to fit in the same spot on the table. Suspicious!

Later, J.J. “CookieMan” Thomson conducted an experiment where he found that neon ions passing through fields have 2 different trajectories, which to him suggested that neon atoms can have different masses. This already showed that Dalton was off, and atoms of the same elements can and in fact sometimes do have different masses. But why? This wouldn’t be answered until much later.

Protons, the second time around

Remember Goldstein? Well, most people don’t. So nobody really cared about the fact that he hypothesized protons early on. But when Rutherford says that protons exist, well, everybody listens.

In 1918, Ernest “Nucleus” Rutherford discovered that when you bombard nitrogen gas with alpha particles, hydrogen nuclei are emitted. Since the hydrogen could have only come form the nitrogen, he figured that nitrogen contains hydrogen nuclei, which supported the fact that hydrogen had the smallest atomic weight of 1.

So Rutherford figured hydrogen nuclei are really an elementary particles, and since they’re known to be positive, this meant one thing- protons. It wasn’t long before the charge, 1.602 * 10 ^ − 19 C, was discovered, and later the mass,1.67 * 10 ^ − 27 kg.

Now here was a problem- Rutherford measured the mass of atoms, and the mass of the protons they contained, and discovered that the atoms were significantly fatter than the sum of the protons. This could mean only one thing…

Neutrons- the other guys

In 1928 (long time later, huh? Guess it takes time to make genius), Walter Bothe observed that when you bombard beryllium with alpha particles, you get an electrically neutral emission. He thought that this was a special type of gamma radiation, or something.

But then James Chadwick exposed different elements to the beryllium radiation and measured the effects. He found out that the mass of this thing, whatever it was, was way too big to be gamma rays, and he reasoned that they’re subatomic particles. Let’s call them neutrons, because they’re neutral.

And hey, this explains everything- the isotopes (different number of neutrons will result in the same element but a different mass), the mass discrepancies between protons and nuclei… now it all makes sense. Hurray for Chadwick.

And now the problems

It seems like we have a nice model of an atom now, with a nucleus full of lovely protons and neutrons, and funky little electrons orbiting it randomly. So, is this the end of our atomic theory quest?

Nope. There’s a major problem with this model. According to simple physics, an orbiting charge would has to steadily lose energy. This means electrons orbiting the nucleus would eventually collapse into the nucleus, which would be a very bad thing as it would mean all matter is unstable by nature.

The Rutherford model also didn’t explain emission spectra- when atoms of elements are excited (heated), emitting lights only at certain frequencies- discrete spectra. These are unique to each element. It made sense that this phenomenon had something to do with the orbiting electrons, but if these are just randomly floating about the nucleus, shouldn’t the spectra be random?

These problems seem pretty solid, but all took is a few theories by Planck and Einstein (yes, the guy) to allow a nice Bohr guy to develop a whole new model…

To be continued in Part 6