Structure of an Atom

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Although the word ‘atom’ is borrowed from a Greek word which means indivisible, we know that that doesn’t hold true anymore about the atom. We now know the atom is composed of electrons, protons, and neutrons. Then protons and neutrons are further made of quarks bonded by the strong interaction through force mediating particles known as gluons.

Now how do we know all these?

The experts of this field, the particle physicists a.k.a. high-energy physicists, are able to determine the constituents of tiny particles by smashing them together in gargantuan devices called particle accelerators and colliders. Basically, the higher the energies these devices are able to generate, the more scientists can peer into the particles’ innards.

This year, 2009, particle physicists will be given the chance to peer even deeper when the largest collider ever built goes operational. The Large Hadron Collider (LHC) at CERN will be capable of colliding two protons at energies of 7 TeV each. No collider has come close to reaching these magnitudes.

One of the precursors of today’s particle accelerators was the apparatus used by Ernest Rutherford in his popular Gold Foil Experiment. By directing a beam of alpha particles to a gold foil and observing how they were scattered after collision, Rutherford was able to refute JJ Thomson’s earlier model of the atom.

This simple experiment, which allowed fast moving projectiles (the alpha particles) to collide with a steady target (the gold foil) showed that atoms didn’t have a plum pudding structure as suggested by Thomson but rather that it (the atom) had a very dense positively charged core.

Simple devices like this later on evolved to larger and more sophisticated machines using higher energies. What’s more, the collisions no longer only involved projectiles and fixed targets. Instead, experiments in colliders like the LHC bring two fast moving particles to head-on collisions. Subsequently, it allowed us to discover tinier and tinier particles.

Using particle accelerators and colliders, we have found that the atom has an order of magnitude of 10^-10 m; the nucleus, 10^-14 m; the neutron and proton, 10^-15 m each; the electron, 10^-18 m; and the quark, 10^-19 m.

It’s not only high-energy physicists who are interested in knowing what secrets lay hidden in even smaller orders of magnitude. Astronomers, who are normally more concerned with structures of the largest scale are also curious. Apparently, they believe a better understanding of the tiniest particles can provide valuable clues as to how the Universe came into being.

We have some articles in Universe Today that are related to the atom structure. Here are two of them:

• Quarks
• Standard Model

Articles about the structure of an atom brought to you by Physics World, here are the links:

• Particle physics: the next generation
• Introducing the little Higgs

Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:

• Before the Big Bang

• The Big Bang and Cosmic Microwave Background

Sources:
Wikipedia
GSU Hyperphysics
How Stuff Works
CERN

Tagged as: atom, electron, proton, quark