How do you know when something’s real? Is it enough that its existence is predicted mathematically? What if you use an instrument to measure its effects on other things? Or is seeing truly the only path to believing? Atomism, the idea that all matter is made of fundamental, discrete, indestructible units, has been around for ages, at least since ancient Greece. Back then, it was more of a philosophic idea rather than anything that could actually be tested. The evidence for atoms began to stack up in the 1800′s, but they couldn’t actually be imaged until 1951, facilitated by the technique of field ion microscopy.
Today, showing off atoms is almost a novelty, as IBM has proven able to maneuver single bits of carbon around to create images and even a stop-motion film. There’s no denying that atoms exist, baby. The proof is in the pudding. But is there pudding in the atom? That’s what one historic model predicted. Despite the romantic notions of foregone generations, atoms are not the indestructible bases for everything; there are other little scraps of matter that come together to form them. So what does it look like inside the atom? It’s been a subject of debate (and calculation), but thanks to an international team of researchers, we’ve finally been given our first real glimpse.
Still image from “A Boy and His Atom,” the nearly inconceivable stop-motion carbon atom film by IBM
John Dalton is credited by most as the originator of modern atomic theory, as he noticed that chemical elements always react in ratios of whole numbers. That wouldn’t be necessary if a substance could be broken into infinitely small parts. But that didn’t prove atoms weren’t themselves made up of smaller things. In 1897, J. J. Thompson discovered that cathode rays are actually composed of tiny, negatively charged particles (eventually dubbed “electrons), and he hypothesized that they originated from within atoms, casting doubt on the indivisibility issue. Since atoms have no net electrical charge, Thompson suggested as a counterbalance that electrons were distributed through a sea of positively charged material within the atom, as if they were raisins suspended in plum pudding. A delicious yet ultimately inaccurate view.
A Christmas treat or the basic building block of everything?
Ernest Rutherford took the next high profile shot in 1909, hurling positively charged alpha particles at gold foil sheets, playing a hunch that bet against the Thompson model. Sure enough, Rutherford saw what he wanted when most of the alpha particles slipped right through the foil, with a few being deflected at extreme angles J.J. wouldn’t have expected. Like charges repel, so for the majority of alpha particles to pass through undisturbed, the positively charged parts of the gold atoms had to be almost vanishingly small compared to their atomic radius. The plum pudding was dumped and we were left with the unsettling conclusion that most of the atom was nothing at all; negatively charged electrons orbiting a positively-charged nucleus at a distance much vaster than the particles’ sizes. Turns out there’s not much more to see than empty space.
Niels Bohr continued the “solar system” idea of an atom, but with an important and freakish difference. If an electron circling a proton (which is pretty much a hydrogen atom) were subject to regular electrostatic forces, it would rather rapidly spiral into the nucleus and we’d have no atoms at all. Bohr instead proposed in 1913 that there were certain stable orbital paths surrounding the nucleus in which the electron wouldn’t lose energy and could perpetually stay put unless excited to a higher state. The mind-numbing implication here is that when an electron changes energy levels (orbits), it literally DOES NOT EXIST from the time it leaves one and reappears at the next. Planets don’t pull that kind of shit. This was one of the first inklings of the revolutionary science of quantum mechanics and appears to reflect genuine reality, as Louis de Broglie mathematically refined the idea in 1924.
Don’t look for those electrons in-between. From thephysicsmill.com
But it gets even weirder! The probability function of the Schrodinger Equation, the meat and gristle of quantum mechanics, predicts not circular but a SPHERICAL shell for the innermost electron orbit. In fact, as you might have surmised from the term, you can only really guess at where the electron might be on that spherical shell, not really where it is at any one point. That’s just the beginning, though. Further orbitals take on completely unintuitive shapes with rings and squashed lobes.
How can you believe any of this stuff? These are all necessary, mathematical consequences of quantum mechanics, a discipline the predictions of which are just too accurate to deny. It’s so hard to contemplate because it’s alien compared to anything we’re used to seeing up here in our macroscopic world. As mentioned above, IBM has taken the lead in imaging the infinitesimal, so that maybe it’ll all seem more real if we can actually see it for ourselves. They obtained the first complete image of a molecule in 2009, molecular orbitals in 2011 and atomic bonds themselves last year, but they were scooped a couple weeks ago.
That right there is a hydrogen atom’s electron wavefunction captured by Aneta Stodolna, Marc Vrakking and company using what’s called a quantum microscope. They were able to produce the image through interference patterns after the hydrogen atoms were ionized. Not quite like what Niels Bohr imagined, but probably still fitting for the 100 year anniversary of his model.
What Does This Mean?
If mathematical predictions aren’t enough for you, and you really have to see it to believe it, then there ya go. We’ve gone from viewing atoms themselves all the way down to the fuzzy electron probabilities around the outside. Our perception doesn’t always match reality, so it’s nice to know that with a little ingenuity, we can still see some fundamental truths for ourselves.