Saturday, July 13, 2013

More notes on "The Disappearing Spoon"

[continued from previous post]

Part I   "Orientation: Column By Column, Row by Row"

1. Geography Is Destiny: H, He, B, Be, Sb

Page 21, bottom of page:
Egyptian women were applying a different form of antimony as mascara, both to decorate their faces and to give themselves witchlike powers to cast the evil eye on enemies.
They used stibnite in which you can still see the Latin origin of antimony's chemical symbol, Sb. Stibnite gave the blueish black look which is still alluring, though antimony has been removed from reformulated modern eyeliner. The alchemist's symbol for antimony is:

which sort of resembles an upside down version of the female symbol.

Kean writes at length about Gilbert N. Lewis, as have I. My take on him is here and here.

Now on to some substantive descriptive chemistry: Page 24, bottom:
As we move horizontally across the periodic table, each element has one more electron than it neighbor to the left. Sodium, element eleven, normally has eleven electrons; magnesium, element 12, has twelve electrons; and so on. As elements swell in size, they not only sort electrons into energy levels, they also store those electrons in different shaped bunks, called shells.
Early German quantum mechanics called this Aufbau or building up. Kean describes how electrons build shells -- s, p, d, and f orbitals -- in a logical way. His descriptions of p-orbitals as a "misshapen lung" and "d-orbitals" as balloon animals is amusing, but I would explain it differently. They more resemble blobs with 0, 1, 2, and 3 nodes as described here.

What Aufbau builds on is how electrons self-organize around an increasingly charged nucleus in moving from hydrogen to higher and higher elements. Start with the simplest atom having one proton and one electron. The very first electron goes into a spherical shaped 1s orbital surrounding the proton. Now if we add another proton to that picture to get to the next element (helium), we must add a second electron. It too goes into the same 1s-orbital and two electrons are happy as clams--perfectly-paired. The pairing of electrons is one of the most sublime aspects of electronic theory and is one which I struggle to understand.

Now move on to element 3, lithium: the third electron cannot occupy the same orbital space as its first two, so it must go into a higher energy orbital, the so-call 2s orbital. The 2s orbital is not exactly just a larger s-orbital; it actually interleaves with the 1s orbital as I drew attention to here:

The fourth electron in element 4, beryllium, perfectly pairs with the third one and fills the 2s orbital. Now, the fifth electron in boron could go into what's called a 3s orbital depicted above, i.e., electrons could just keep building higher and higher energy shells of spherical symmetry, but something else happens. A different type of node appears which breaks the spherical symmetry, creating what's called a p-orbital:

The 2p-orbitals are lower in energy than the 3s orbitals and that's why the next 6 electrons fill those first. There are 6 spaces because the electrons pair and go into 3 different p-orbitals -- one for each Cartesian dimension, x, y, and z.

[more soon]

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