The Periodic Table

 

Ahhhhh, I remember when this table looked like a mysterious collection boxes with archaic symbols and numerical values (that made little to no sense at all). Do they make any more sense now than they did back then?

YES! And that’s what I like to call progress.

Nowadays I don’t have as much use for it as I did back when I was studying Chemistry like a mad man (for I, poor soul that I am, studied in the IB). But fuck, back then it was hella useful! There’s a shit ton of information packed into such a nice graphic format (often made more interactive with the magic of the Internet!) – for instance, you can get an Element‘s Electronegativity, Valence Shell Electrons, and Oxidation States from most Periodic Tables that I know of (and I only keep the “cool beans” ones on tap).

A basic Period Table would have the bare bones information printed – the atomic symbol, the atomic number, and the Relative Atomic Mass (written in atomic mass units [amu]). My fave Periodic Table is the one on ptable.com – It’s pretty tight, check it out!

 

So let’s get into some of the Physics and shit. Why’s the Periodic Table shaped the way it is? What’s so gd periodic about it?

Well, Quantum Mechanics has a lot to say about both! Well, for the periodicity at least. The shape of the table is just for convenience (and now that I think about it, at least the “row-column” format is based on the results of the quantum atom).

 

The “periodicity” of Chemical Elements refers to the fact that, as you start adding more and more protons and electrons to an Atom (you can’t really do that in practice, just bear with me) the chemical properties of the atom in question starts to resemble other atoms (to a certain extent).

firstie
Periodic trend in first ionization energy (the energy required to remove one electron from element)
CNX_Chem_06_05_Radiigraph
Periodic trend in atomic radii (implies discrete energy levels for electron orbits)

For example, all the Halogens steal one of Sodium’s electrons pretty sneakily, whereas Sodium and it’s Alkaline Metal buddies all generously give out one electron to any of the aforementioned ninja Halogens.

This was (and still is, for that matter) seen, studied, and investigated by way of Chemical Reactions. Chemists and the like started noticing various trends in the elements, and various Physicists got together and decided “Quantum Mechanics: genius!” and boom, you’ve got a full-fledged theory that describes the properties of the elements to a tee.

Those physicists were investigating the Emission Spectra of the elements, and were trying to explain why the fuck it was all quantized up in here. Bohr gave his spiel about Hydrogen, people thought “k” and moved on – but then Shödinger was like “nah bruv!” and let him have it. Shrödinger’s Wave Function for the electron in Hydrogen (treated like a particle in a Potential Well – as you do) can be solved, and matches Bohr’s
successful model for Hydrogen, except he can proudly say “Least I didn’t pull the quantization of angular momentum outta my ass, unlike sommmebody did
*cough**cough* Bohr!*cough*”

Yeah, so it’s all a lil fuzzy at the moment, mathematically that is (we’ve got training wheels still, we’re first years ffs) but I know the gist of it. Shrödinger’s Wave Function can be solved for more complicated Atoms of Z-protons and Z-electrons (treated with the Central Field Approximation) to give predictions for the Emission Spectra of the Atoms. Funnily enough though, you need something extra (seems kinda ad hoc to me) to explain it fully, and it’s called the Pauli Exclusion Principle.

The long and short of it is “No two electrons may have the same Quantum State” which means, pretty much “you can’t have two atoms in the same principle energy level with the same orbital angular momentum, the same magnetic moment, and the same spin angular momentum values”.

It puts a limit to “how much the electron wave functions can overlap” so to speak (straight from mah lecture notes). Otherwise, any old atom in it’s “ground state” would want to have it’s electrons in the most energetically stable state i.e. aaaalll the way down where the ground state of Hydrogen is at. Although, no, not really, electrons dislike touching their own kind – but they’d be closer to each other (in terms of their energies, that is) than the spread we see in reality, that’s for sure.

So read up on the solutions to the Shödinger Wave Function for many electrons, and behold the power of physical models! If you wanted to know how to “read” the Periodic Table, I’d recommend you either attend your Chemistry classes, and/or Google it, or find yourself a nice lil Youtube video or smth to sate your curiosity.

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