Trumpet Voluntary - the Triple Bond

Ok, it now behests me, after coming full circle with this blog, to demonstrate the power of what can be learned. This post is just about the most difficult to understand of them all.

The story starts thus: Chemistry talks about "bonding" between atoms. That is, for example, when you get wet, you are not spattered with either oxygen or hydrogen, but water, and water is simply H2O - two hydrogen atoms and an oxygen atom, "bonding" together.

What is this bonding, then? It's when atoms come together rather like Jigsaw pieces do, and they can fit perfectly.

How? Well, broadly, it is this....atoms like electrons flowing around them (yes, FLOWING! after all, moving charges are a current, are they not?) and the number they like to have is about 8 or 16, but they are only happy with certain numbers. Once that "shell" is "full" they become uncooperative (they will not do any more chemistry).

Once the atoms discovered this, they became VERY friendly.

A short course in chemistry is in "order" here.

Electrons, as they whizz, or "flow" around the nucleus (my field of research) like to group together but not always in the same way.

The first group has 2, the second eight, the third eight also. And so on.

Hygrogen was lonely. It has only one electron in a group that wanted two. Oxygen was also lonely, it had the full first group (2) but only six of the second group, which wanted eight.

Then Oxygen and Hydrogen met and their problems were solved in one swell floop!. They could "share" electrons!

Two hydrogens could "share" with oxygen to give oxygen the illusion of eight electrons, whilst hydrogen could "pretend" that both of it's atoms had two!

End of lesson. Well done. That is how water works, said the crying nun.

Now to the point of this post. The above is called a chemical bond. A "single" chemical bond. Oxygen-hydrogen - Easy!

BUT ( there is always one of these is physics, even without the goat) it gets worse. Here's what happens.....

The behaviour of the electrons in atoms can be illustrated by "seeing" where they are. This is where the math comes in, because no-one can actually "see" them.

First off, how do I tell you where I am? Well, right now, I am about 1 meter away from the window and 2 meters away from the the TV in a 90 degress direction. Whoops! I am on the 33rd floor, so I am about 130 meters UP.

That's 3 numbers. One for each dimension. Those 3 numbers tell anybody where I am. It's very easy because I live in a rectangular apartment, and am 130 meters directly up from level ground.

To do the same with electrons is not as easy. They live in a circular apartment and are going round it. Round.... circular.......

Why not use different numbers to tell where the electron is? How about "angle from somewhere" and "how far it is from the somewhere"?

My apartment and I are referred to as "rectangular" coordinates (the three numbers). The electron in the atom can be found by using a more convenient way, using "Spherical" coordinates
(also 3 numbers).

It is now time to show how "easier" it is this way.. copy this link.....

http://en.wikipedia.org/wiki/Spherical_harmonics
(This is the math)

and then this one..

http://oak.ucc.nau.edu/jws8/dpgraph/Yellm.html
(these are the pics that come out of the math)

There are two points to note...1. This is the EASIER way....2. I see past the waves of unintelligible letters in link 1 and all I see are the salient points, which in this case, is the shape of the thing when you draw the picture of it in link 2.

That picture is essential to the understanding of the 021, sorry, "triple bond".

This is another thing I failed to understand. I got the single bit, but double and even triple bonds? Try as I might, my teachers were unable to tell me what they were.

Here is why....

In the chemistry of Carbon, this element has 6 electrons, 2 (full shell) plus 4 (half the next shell). It would like four more. It gets this with hydrogen , but whereas oxygen gets 2 hydrogen atoms, carbon gets 4, to give it the eight electrons it "needs" The molecule formed is "methane", the simplest hydrocarbon ( see my previous post on oil). CH4.

But sometimes, there are only 2 hydrogens available, and what we see is the "double bond", that is, the carbon has a "double bond"with itself and with only two hydrogen atoms, double "2" making four. C2H4 - Ethene. What happens when there is only one hydrogen? It does complex chemical gymnastics and does a "triple bond" with itself and the one hydrogen.

It is best to think about this with "hooks and fish". Hydrogen has one hook, carbon has four hooks or fishes.

Carbon wants a full shell, either by losing four or gaining four, electrons, it doesn't care which.

For 2 carbon atoms, it is easy, just "share" the outer four and both can pretend that either have 8 ( a full shell). In this case, carbon is definitely heterosexual. It doesn't happen.

But HOW can we visulise this, after all, pictures often help. This is what none of my teachers were able to do.

Take the simplest Spherical Harmonic, the ball-shaped "cloud". Hydrogen atoms each have one of these, and when they overlap - cool! we have H2, or chemical hydrogen, two electrons sharing one "orbit", but how can four electrons share one orbit? This is the clever bit. This is the point where the maths take over. Have a look at the oak pictures (second link). Only the first one is like a ball, all the others have different "bits" sticking out of them, like the balloon sculptures that clowns make. Well, the key is understanding what the bits actually "mean".

The reason they are that shape is that the further out the electron gets from the nucleus, the more angular momentum it has, and using Spherical Harmonics is the only way to illustrate this.

For example, carbon looks like the Y(2,1) picture, basically a 4-pointed star. You can't see it, but there is an extra one in the middle, the "ball" shape. Imagine two of these face to face. Red bits opposite the red bits, blue opposite blue. Push them together and they overlap just like hydrogen's "balls". THIS is the triple bond. Red-red, blue-blue and the "ball" shape which is not shown . 1, 2, 3 electrons being "shared" .

The way to really understand this is to think of the shapes as "probability densities" that tell you just how likely it is to find an electron in "that" shape.

If you put 2 carbon atoms together like this, they form a "triple bond", and remembering that Carbon likes to have 4 hooks, with three hooks already taken with the triple bond, stick a hydrogen on and each of those left, you have the molecule H-C-C-H, which is called "Ethyne".

What has just been "explained" here is not chemistry, but "quantum chemistry", and along with powerful math, gives a beautiful explanation of how chemical bonding works. If you didn't understand, don't worry, it took me a good 4 years to work it out.