# The Atom

Waaaaaaay the hell back, when the majority of people lived to be, like, 50 yrs old tops, and when the young’ns all listened to their elder’s explanations for anything and everything that they couldn’t quite wrap their lil heads around like it was the law, people… Actually were pretty spot on when they thought that everything was made of lil itty bitty thingies that were indivisible.

They called em Atoms (well, atomos cuz they were ancient Greeks or whatever) – and when I say “pretty spot on”, I’m referring to how they thought they were indivisible whereas that ain’t true!

We know this nowadays, the evidence for this is pretty explosively (more importantly, demonstrably) clear as day.

There’s lots to talk about Atoms, but let’s stick to the Physics of it all, rather than the politics (always open to the discussion though – human interaction, lots of fun, 10/10,  would recommend (that I would do more of (it))).

So, let’s get some shit outta the way. What’s the basic structure of an atom?

Familiarize yourself with the experimental results of John Dalton who found that it made sense to think of Chemical Elements as atoms by studying how combinations of chemical elements (undergoing Chemical Reactions) always combine in ratios of whole numbers, and of Einstein (again?) who proved the existence of Molecules by doing a statistical analysis of Brownian Motion.

Thomson discovered the Electron, Rutherford discovered the nucleus (the atom’s core), and further results (like the discoveries of Isotopes, the Neutron, Nuclear Fission and Radioactivity) helped put the pieces of the atomic puzzle together.

Any Atom is categorized into it’s element (is it gold, or is it silver?) and further into which isotope it is (it seem heavier than usual?) – what element and isotope it is depends on the amount of Protons and Neutrons respectively. An Atom is usually stable and has no charge (it’s neutral) – so there’s a special name for Atoms with a net charge – Ions (after the Ionian peoples, for some reason).

There’s a handy table – the Periodic Table – that illustrates for us all of the known chemical elements – and it’s a god-send for all Chemistry students.

That’s all pretty much old news though! And you thought it couldn’t get more interesting, well, IT CAN! I’m tellin ya, calm down.

Because now we’re getting Quantum!

Turns out that atoms emit Energy (in the form of Light) only at discrete wavelengths – i.e. only at certain discrete amounts. And only certain atoms emit certain wavelengths, giving each element it’s own “finger print”. This is called the Emission Spectrum, and it’s what we mean when we say that “energy is quantized”.

In order to be able to describe this, a guy named Niels Bohr thought of what the Hydrogen atom (1 Proton, 1 Electron, (Neutrons need not apply)) looked like. He thought of the electron as though it orbited the nucleus like a planet orbits another. So far so good, nothing crazy, right?

Well, he added the further constraint that Atoms may only have certain specific energy levels (energy going to the electrons), which (thinking real hard here, Circular Motion…) corresponds to electrons orbiting only at specific radii, increasing in radius the higher the energy of the electron. Means no electrons exist between there, at all.

Therefore, his explanation for the quantized energy being emitted, is that the Photon being emitted has the energy (lost in transitioning between energy levels) making up the difference between energy levels, as described by Einstein’s result from his study of The Photoelectric Effect $E=hf$

Ok, it’s something. It gives us a little to grab onto if we wanted to say why the energy is quantized. Some further support for the idea comes in the form of de Broglie Wavelengths and how the electrons need to be a standing wave – so if it increases in energy, then duh, give it some space! Bohr’s Model of Hydrogen gives rise to the quantization of Angular Momentum and the concept of Quantum States – the basic result coming from de Broglie $p = \frac{hf}{c} = \frac{h}{\lambda}$ and with the constaint of a standing wave, then ${\lambda} = n\frac{h}{p}, n \in N$ – n being the “principle quantum number”.

——–more on this later——–