The Atom

Demokritos, Rutherford, Bohr and Pauli

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3. The Atom

— Demokritos, Rutherford, Bohr and Pauli —

The Democritus Atom

postulated the atom

The idea of atoms has been around since the fifth century BC when a jolly philosopher named Democritus opposed the popular idea of the four elements (fire, earth, water, air) and argued that everything is made up from elements that can not be divided any further. He called these elements a-thomos, which means in-divisible. It took humanity two and a half millennia to develop the technology needed to pierce through to the level of those smallest indivisible things, and when experiments verified the existence of those structures we now call atoms everybody thought they had found Democritus' in-divisibles. That's why they called them atoms. (Like Columbus naming the American Natives 'Indians'. Same thing.)

Ernest Rutherford
split the atom

Backs were patted, applause sounded, medals of valor shifted shaking hands, but, as with any theory, there was something fishy about the atom, something that couldn't be explained. In 1911 a man named Ernest Rutherford was shooting so-called alpha radiation at a thin sheet of gold (while hollering Onward Christian Soldiers full blast through the lab). What he didn't know and what nobody knew was that the alpha-particles that make up alpha radiation were in fact the bare nuclei of helium atoms. And he was shooting them at gold atoms.

alpha particles bumping into gold nuclei

Most of the alpha particles zipped clean through the gold but some were diverted and some even bounced straight back. By the way the alpha particles behaved Rutherford concluded that 99% of an atoms mass was concentrated at the core. Atoms weren't indivisible at all! They had some kind of inner structure. Bummer!

The Bohr Atom

Cries of dismay ripped through the realm, glory was rescinded, champagne poured back in the bottle. But a fine young man named Niels Bohr saved the day by coming up with an atom-model that has been known as the Bohr Atom ever since.

Niels Bohr
Niels Bohr
drew up the atom

Now Niels was not an exceptionally smart man, he just had a vivid imagination, and, according to Einstein, that is often more important than raw processor speed. Niels figured out that what we call an atom is in fact a tiny nucleus surrounded by a cloud of electrons. These electrons, Niels demanded, were situated in spheres around the nucleus and they could jump from one sphere to a larger one by absorbing one quantum of energy (which is exactly one photon because besides lighting everything up and keeping everything together, photons also make everything move).

That was in 1913 and although Bohr received the Nobel Prize for physics in 1922 for his atom model—which still stands today—it failed to explain why there were so many different elements. Elements as found in the periodic table are the way they are because electrons don't just simply huddle around the nucleus in the tightest ring but refuse electrons to join when a ring is full. Hence some electrons are kept in outer rings and elements maintain their uniqueness. How do atoms do that?

Pauli's Exclusion Principle

Wolfgang Pauli
Wolfgang Pauli
explained the atom

The answer came in 1926 by a young genius named Wolfgang Pauli who postulated the Exclusion Principle. It roughly states that no fermion (such as electrons) can share a spot with another one (and remember: a 'spot' for a quantum particle is a blur of most likely spots). This in contrast to bosons which can be piled upon the same fermion until it is blue in the face. Pauli discovered that electrons have a total of four characteristics, some of which can have two values (1 or 0; yea or nay, etc), leaving the electron eight separate states to exist in. The Exclusion Principle states that two electrons that have identical values for those four characteristics can not occupy the same sphere around the nucleus. Hence only eight per sphere are allowed and the elements were explained.

The Creator deemed it fitting to not only give all quantum particles sovereignty in matters of their progression; electrons were also given an ineluctable unique perspective on the nucleus they were orbiting. The so-called limitation of a quantum's sovereignty doesn't actually limit the particle; it forces it into unicity.

Hold that thought (3):

The Exclusion Principle: Two electrons that have identical values can not occupy the same position relative to the nucleus.

Before we dive into the really cool stuff, we have to make one more stop: the nursery, where all those free living quantum creatures are born from cabbages way beyond any cabbage you've ever seen...

Go to the next chapter:
Quantum Foam

Summary 3: The Atom: Democritus, Bohr, Rutherford and Pauli

  • Atoms consist of a tiny nucleus surrounded by electrons that are kept together by means of the electromagnetic force.
  • All electrons have a unique perspective on the nucleus they are orbiting.

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