Last week in class we were asked to draw lines on a piece of paper to make six boxes. In one of the boxes, we were to write down all the homonuclear diatomic elements. The first thing that came to mind was all of the halogens: fluorine, chlorine, bromine, iodine, and astatine. We then formed groups to compare answers. To my surprise, I was the only one with astatine in the box as diatomic. So is astatine a diatomic element? It generally is not considered diatomic but I decided to search myself. Astatine is a radioactive element and the heaviest of the naturally occurring halogens. Wikipedia labels astatine as diatomic but states: “Astatine is so rare in nature (its most stable isotope has a half-life of only 8.1 hours) that it is usually not considered.” Astatine is often times considered the rarest naturally occurring element on earth which may be yet another reason why it is neglected as diatomic. “Astatine is the rarest naturally-occurring element, with the total amount in Earth's crust estimated to be less than 1 oz (28 g) at any given time; this amounts to less than one teaspoon of the element.”
A research paper published in the journal of physical chemistry entitled: Characterization of Homonuclear Diatomic Ions by Semiempirical Morse Potential Energy Curves. 1. The Halogen Anions, has done extensive research on astatine and the other halogen elements. The research paper focuses on potential energy curves of the halogens. Astatine is almost entirely in its homonuclear diatomic state through the research paper. The diatomic state of astatine is labeled as the ground state or lowest energy state which suggested astatine prefers to be in the diatomic state. Furthermore, astatine follows all the same trends as the other halogens throughout the research article which would suggest that if the five former halogens are diatomic, then astatine should be also.
Astatine follows nearly all the trends of the other halogens. If only it were present in greater quantities on earth, then it would most likely be considered as a regular diatomic element. Because it is so rare however, it is generally disregarded entirely as a diatomic element.
http://pubs.acs.org/cgi-bin/article.cgi/jpchax/1996/100/i23/pdf/jp953601z.pdf
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