It has come to my attention that the Japanese government have published a map of the tellurium-129m contamination levels in the countryside near to Fukushima. Here is a link to the maps from Japan.
Now before we get going we might want to consider what tellurium is.
Tellurium is a heavy version of sulphur (sulfur), it is named after the earth while selenium (the element) above it is named after the moon. Tellurium has some rather interesting chemistry it is more than just a heavy version of sulphur.
Many organisms are able to transform it from one chemical form to another, one of the typical symptoms of tellurium poisoning in humans is that the unlucky person who is stricken with tellurium will start to stink to high heaven of garlic.
This is because inside the human body the tellurium is converted into dimethyl tellurium, while I do not think that the tellurium will leave the reactor in the form of dimethyl tellurium I think it is likely that bacteria or animals will convert the tellurium into this volatile form. It is possible that the ability of living things to form this volatile organometallic may make the environmental chemistry of the tellurium more complex.
Now I hope that it is OK with my readers but right now I do not want to get sucked into a discussion of the environmental chemistry of tellurium, but I am willing to comment on another aspect of tellurium chemistry.
One of my all time favourites in chemistry is VSEPR, or Valence Shell Electron Pair Repulsion theory. For those of you who are not in the know, this is a simple theory which predicts correctly the majority of covalent compounds which lack transition metals. Be careful of the transition metals the electrons in the d orbitals can throw you a bit of a weirdo ball, on the other hand the main group elements tend to just play nicely with a normal over the shoulder delivery of the cricket ball without trying to do things like spin bowling.
The core idea of VSEPR is that the central atom has a series of electron clouds (orbitals) which poke out of the atom to form sigma bonds. The sigma bonds would look like sausages if we could see them. Think it is a nice thing that s is for sausages and also for sigma bond.
These sausage like clouds of electron density will repel each other, this is a plain simple electrostatic effect much like the effects you get if you comb your hair and then wave the comb near some small scraps of paper.
If an atom has two such sausages (opps I mean bonds) then the furthest they can be from each other on a sphere is at 180 degrees (pi radians) from each other, an example of this would be the arrangement of atoms in acetylene.
If an atom has three sausages then the furthest they will be from each other is at 0, 120 and 240 degrees around the equator of a perfect sphere. An example of this type of arrangement would be the atoms in benzene or styrene. While we are at it be thankful for styrene, without styrene there would be no polystyrene or ABS plastic. The chances are that your computer screen has a case made of ABS.
If an atom has four sausages then these bonds will be arranged in a tetrahedral manner, this is the arrangement which makes them the furthest from each other.
If the atom has five sausages then the geometry which puts the bonds the furthest apart would be to stick one at each of the poles, and three spaced at 120 degrees apart on the equator. One alternative would be a square based pyramid but I have done the maths for that
If the atom has six sausages then the geometry which puts all the bonds in an octahedral arrangement.
When an atom has a lone pair this should be regarded as a sigma bond which goes to nowhere. Treat it as if it almost as it it was just another bond, as the electrons are on average closer to the atom the lone pair is more able to repel other other bonds than a normal sigma bond.
The fun thing about tellurium is that sometimes its lone pair is stereochemically active this means that it repels other electron pairs just like any other electron pair. But sometimes the tellurium lone pairs are stereochemically inactive which means that these lone pairs do not repel other electron pairs (bonds and lone pairs). The non-stereochemically active lone pair does not normally appear in light elements such as sulfur and oxygen, it tends to be something which only happens with heavy elements such as tellurium and lead.
Filed under: cesium, chernobyl, Cs-137, fission products, Fukushima, Intake of radioactivity, iodine, lone pairs, nuclear, nuclear chemistry, Nuclear fuel, radiation, radioactivity, silver | Leave a Comment »