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Reckless use of pesticides

Dear Reader,

It has come to my attention that a person in the USA caused the deaths of four members of his family when he attempted to use a restricted pesticide to kill bugs at his home in Texas. What this man did was to use a product which is not intended to be sold to or used by the general public. In the UK the use of this chemical is strongly limited to professional users who have to undergo special training before they use it.

It was aluminium phosphide, this is one of the more dangerous pesticides which is in current use. It is a solid which on contact with water (or acids) will generate phosphine gas. The take home message is if you face a pest control job which you can not solve using over the counter products sold to the general public then unless you have the special training (and equipment) required to use a professional use only product then leave work with such a product to a professional (and I hope competent) pest control worker.

You might wounder what aluminium phosphide is, it is AlP, it is a solid with the same crystal strucutre as zinc sulfide (zincblende). Here the aluminium and phosphrous atoms have tetrahedral coordination environments. This is a compound with a cubic cell (a = 5.451 Å). The fractional coordinates of the atoms are

Al 0, 0, 0

Al ½ ½ 0

Al ½ 0 ½

Al 0 ½ ½

P ¼ ¼ ¼

P ¾ ¾ ¼

P ¼ ¾ ¾

P ¾ ¼ ¾

We can make a xyz file for a single unit cell.

XYZ file : Unit cell AlP
Al 0 0 0
Al 5,451 0 0
Al 0 5,451 0
Al 5,451 5,451 0
Al 0 0 5,451
Al 5,451 0 5,451
Al 0 5,451 5,451
Al 5,451 5,451 5,451
Al 2,7255 2,7255 0
Al 2,7255 2,7255 5,451
Al 2,7255 0 2,7255
Al 2,7255 5,451 2,7255
Al 0 2,7255 2,7255
Al 5,451 2,7255 2,7255
P 1,36275 1,36275 1,36275
P 4,08825 4,08825 1,36275
P 1,36275 4,08825 4,08825
P 4,08825 1,36275 4,08825

Here are three views of the unit cell for you to look at




It should be clear that the empirical formula of the compound is AlP. We have eight aluminiums at the corners of the cell, each is shared equally between eight cells, we also have six aluminiums on the faces. Each of these six aluminiums is shared between two cells. This gives us a total of four aluminiums.

We have four phosphorus atoms (in a fetching orange) which are totally inside the unit cell. Thus we have a 1:1 ratio of aluminium to phosphorus atoms.



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