The diagram of an atom is among the most familiar symbols of science there is. Unfortunately, it’s not actually what atoms look like, and we’ve known that for nearly a century.
The history of the atomic model is long—we could go back as far as the ancient Greeks, really—but for our purposes, we can start around 1900. It was about then that Sir Joseph John Thomson discovered the electron, which is the negatively charged part of an atom. He proposed that these electrons were captured in uniform spheres of positively charged matter. This was dubbed the “plum-pudding model,” since the electrons in the positive substance is a bit like plums in English pudding. New Zealand physicist Ernest Rutherford discovered that if you shoot positive particles at atoms (in the form of gold foil), they don’t all bounce off the way they should if there was a large mass of positive “pudding.” Instead, some bounce off, but most pass through, suggesting that electrons are spaced around a small mass of positive substance—a nucleus, if you will. He rejiggered the model in 1911 to have electrons orbiting a nucleus the way that planets orbit the sun, which was dubbed the “planetary model,” for obvious reasons. The planetary model has become the most famous symbol for the atom—even though it was refined only two years later by Danish physicist Niels Bohr.
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The problem with the planetary model is that electrons would lose energy by orbiting, causing them to collapse into the nucleus. Bohr’s model solved this: instead of orbiting willy nilly, electrons orbited only at very specific energy levels. Electrons could jump from level to level if they absorbed or released energy, but they never drifted between levels. The Bohr model is probably the most popular in science textbooks (you’d recognize it as a nucleus surrounded by ever larger circles of electrons) but—you guessed it—it’s mostly wrong, too.Steven Dutch of the University of Wisconsin Green Bay clearly sums up the next step in the atomic model: “By the 1920’s, physicists had discovered that matter also has wave-like properties and that it just doesn’t work at the atomic level to regard particles as tiny points with precise locations and energies. Matter is inherently ‘fuzzy.’ They gave up thinking of electrons as tiny planets altogether.” Electrons don’t really follow paths at all. Physicists discovered that they’re actually quantum particles that exist in many different places at once. They still occupy individual energy levels, but instead of a path, each electron’s many-places-at-once location could be thought of as a cloud. That’s why it’s known as the electron cloud model.
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That’s not to say Bohr was wrong. It’s a good way to simplify a very complicated concept, and it actually works surprisingly well for simple atoms like hydrogen. But the electron cloud model illustrates the latest knowledge about the structure of an atom. The planetary model is pretty, but reality it ain’t.
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written by yousef kamal