Modern Mythology: Bohring and Outdated
[We’re a couple of days late with MM this week, but better late than never, right?]
So there is this thing that bugs me a little bit from time-to-time. It is the cultural perpetuation of the outdated model of the atom in (most often) commercial logos. Sometimes your favourite skepticism blogs do it too. OOPS.
(I love the Skepchick/ Teen Skepchick logo, really, I do. I’m just pointing this out, okay? ;D)
So, a little bit of history first. The first model of the atom came from the British Physicist J.J. Thompson, in 1904 after discovering the electron in 1897. J.J. Thompson’s model was called the “Plum Pudding Model”, because he proposed that the atom was like a plum pudding, with (negatively-charged) electrons positioned evenly about the positively-charged atom, like currants in a plum pudding.
In this experiment, Rutherford and his students Hans Geiger and Ernest Marsden shot alpha particles at very thin metal foil. According to Thompson’s model of the atom, the forces exerted on the alpha particle by the positive atomic charges were expected to roughly cancel the forces from the electrons so that the alpha particles would be observed deflecting only slightly. What they observed, however, was some of the alpha particles were deflected at very large angles and some were deflected right back toward the source. Rutherford himself described this observation: It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.
This discovery led Rutherford to envision an atom in which negative electrons orbit an unbelievably small, massive (as in: having mass), positive nucleus, quite like a miniature solar system. This model came to be known as the nuclear model of the atom.
This model was very successful, however there were several problems with this. The nuclear model of the atom failed to explain why atoms were stable (according to classical mechanics, an electron would spiral into the nucleus while radiating energy as an electromagnetic wave) and why their spectra are discrete (at around the same time, scientists were discovering that matter emits and absorbs light in discrete spectra).
Along came a young Niels Bohr, who wished to explain the first problem with the Rutherford Model, and realised the relationship with the second problem, which led him to propose a radically different model. Bohr’s model stated that an atom consists of negative electrons orbiting a very small positive nucleus, exactly as in Rutherford’s model. However, Bohr proposed that atoms can exist only in certain stationary states, with each stationary state corresponding to a particular set of electron orbits around the nucleus. Without getting bogged down in too much detail, the implications of Bohr’s model turned out to be profound. An atom in its ground stationary state has no states of any lower energy to which it can jump, so this accounts for the fact that matter is stable. Also, an atom can change stationary states by emitting or absorbing a photon or by undergoing a collision so this accounts for the discrete emission spectra.
Bohr originally only proposed this for the Hydrogen atom as it was the most simple. He then tried to extend his model to other atoms, and proposed a ‘shell model of the atom’. This is probably what you learnt at school, and what seems to feature in company logos (FINALLY! you say. She is getting to her point). Look, here is even an actual diagram from my school science exam. The question asked me to draw a sodium atom, so you can see the neutrons and protons in the nucleus in the centre and the electrons in different orbitals around the outside. The orbitals should go in a pattern with two in the first, eight in the second and third until all of the electrons have been used up.
This is almost right. Almost.
Then, because of some complicated stuff to do with quantum mechanics and the Pauli exclusion principle, Bohr’s model of the atom got a bit of an update. It turns out that the electrons aren’t really in ‘orbit’ at all, like you would imagine the earth in orbit around the sun or the moon around the earth, but the electrons are in ‘clouds’, and they get a new notation that works in what are called p, d, s, and f orbitals. They aren’t orbits, but orbitals. An orbit implies some sort of trajectory so you need to know what direction it is heading in and how fast. This isn’t possible because of the Heisenberg uncertainty principle, so all we can say about an electron is its orbital. An orbital is just a bit of space where there is a 95% chance of finding that particular electron. If an electron is in a particular orbital, you know about its energy – but there is no way of knowing how it is moving around within that orbital.
So now you know! It isn’t as easy to draw, and it doesn’t make for pithy company logos, but it is interesting!
Also, did you know that scientists managed to take a photograph of an individual atom last year? It is pretty freaking amazing what they did.
tl;dr? This guy says pretty much the same thing I did, minus the whole history of the atom, plus hula-hoops and balloon animals.
Note: This post was written by a somewhat sleep deprived person who would appreciate it if you happen to spot anything glaringly stupid in this post to please point it out. Cheers 🙂